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[Android Dev] 2.1 Lifecycles
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目录
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<div id="toc"><ul><li><a class="toc-href" href="#onsavedinstancestate" title="onSavedInstanceState()">onSavedInstanceState()</a></li><li><a class="toc-href" href="#asynctasks-and-loader" title="AsyncTasks and Loader">AsyncTasks and Loader</a></li><li><a class="toc-href" href="#using-loaders" title="Using Loaders">Using Loaders</a><ul><li><a class="toc-href" href="#implement-oncreateloader-onpreexecute-and-ondoinbackground-for-asynctask" title="implement onCreateLoader — onPreExecute and onDoInBackground for AsyncTask">implement onCreateLoader — onPreExecute and onDoInBackground for AsyncTask</a></li><li><a class="toc-href" href="#implement-onloadfinished-onpostexecute-for-asynctask" title="implement onLoadFinished — onPostExecute for AsyncTask">implement onLoadFinished — onPostExecute for AsyncTask</a></li><li><a class="toc-href" href="#in-makegithubsearchquery-create-bundle-create-a-loder-start-it" title="in makeGithubSearchQuery(): create bundle, create a loder, start it">in makeGithubSearchQuery(): create bundle, create a loder, start it</a></li></ul></li><li><a class="toc-href" href="#caching-with-loaders_1" title="Caching with loaders">Caching with loaders</a></li></ul></div>
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</div>
<p>Android kills background apps !! </p>
<p><img alt="" class="img-responsive" src="../images/andev_p2e1_lifecycle/pasted_image001.png"/></p>
<p>→ <code>onCreate()</code> → <strong>Created</strong> →<code>onStart()</code> → <strong>Visible(</strong>can be seen on screen) → <code>onResume()</code> → <strong>Active</strong>(get focus, can interact with)</p>
<p><strong>Active</strong> → <code>onPause()</code> → <strong>Paused</strong>(lose focus — same thing as Visible?) → <code>onStop()</code> → <strong>Stopped</strong>(disappeared) → <code>onDestroy()</code> → <strong>Destroyed</strong>(lifecycle ends)</p>
<p>when rotate screen, the function calling is: </p>
<p><code>onPause --> onStop --> onDestroy --> onCreate --> onStart --> onResume</code></p>
<p>note: activity will be <strong>destroyed</strong> when device configuration is changed ! </p>
<h2 id="onsavedinstancestate">onSavedInstanceState()</h2>
<p>so that the app states can be saved when device configuration changes (ex. rotate). </p>
<p>parameter: a <code>Bundle</code> to keep state into key-value pairs.
to pass objects via Bundle: implement the <code>Parcelble</code> interface. </p>
<p>Override this <code>onSavedInstanceState()</code> function → put useful objects into the bundle parameter. </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">3</span><span class="p">)</span><span class="w"> </span><span class="n">Override</span><span class="w"> </span><span class="n">onSaveInstanceState</span><span class="w"> </span><span class="k">to</span><span class="w"> </span><span class="n">persist</span><span class="w"> </span><span class="k">data</span><span class="w"> </span><span class="n">across</span><span class="w"> </span><span class="n">Activity</span><span class="w"> </span><span class="n">recreation</span><span class="w"></span></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="n">Do</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">following</span><span class="w"> </span><span class="n">steps</span><span class="w"> </span><span class="k">within</span><span class="w"> </span><span class="n">onSaveInstanceState</span><span class="w"></span></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">4</span><span class="p">)</span><span class="w"> </span><span class="n">Make</span><span class="w"> </span><span class="n">sure</span><span class="w"> </span><span class="n">super</span><span class="p">.</span><span class="n">onSaveInstanceState</span><span class="w"> </span><span class="k">is</span><span class="w"> </span><span class="k">called</span><span class="w"> </span><span class="k">before</span><span class="w"> </span><span class="n">doing</span><span class="w"> </span><span class="n">anything</span><span class="w"> </span><span class="k">else</span><span class="w"></span></span>
<span class="code-line"></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">5</span><span class="p">)</span><span class="w"> </span><span class="n">Put</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">contents</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">TextView</span><span class="w"> </span><span class="n">that</span><span class="w"> </span><span class="k">contains</span><span class="w"> </span><span class="n">our</span><span class="w"> </span><span class="n">URL</span><span class="w"> </span><span class="k">into</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="k">variable</span><span class="w"></span></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">6</span><span class="p">)</span><span class="w"> </span><span class="k">Using</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="k">key</span><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">query</span><span class="w"> </span><span class="n">URL</span><span class="p">,</span><span class="w"> </span><span class="n">put</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">string</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">outState</span><span class="w"> </span><span class="n">Bundle</span><span class="w"></span></span>
<span class="code-line"></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">7</span><span class="p">)</span><span class="w"> </span><span class="n">Put</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">contents</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">TextView</span><span class="w"> </span><span class="n">that</span><span class="w"> </span><span class="k">contains</span><span class="w"> </span><span class="n">our</span><span class="w"> </span><span class="n">raw</span><span class="w"> </span><span class="n">JSON</span><span class="w"> </span><span class="k">search</span><span class="w"> </span><span class="n">results</span><span class="w"> </span><span class="k">into</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="k">variable</span><span class="w"></span></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">8</span><span class="p">)</span><span class="w"> </span><span class="k">Using</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="k">key</span><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">raw</span><span class="w"> </span><span class="n">JSON</span><span class="w"> </span><span class="k">search</span><span class="w"> </span><span class="n">results</span><span class="p">,</span><span class="w"> </span><span class="n">put</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="k">search</span><span class="w"> </span><span class="n">results</span><span class="w"> </span><span class="k">into</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">outState</span><span class="w"> </span><span class="n">Bundle</span><span class="w"></span></span>
<span class="code-line"></span>
<span class="code-line"><span class="nv">@Override</span><span class="w"></span></span>
<span class="code-line"><span class="k">public</span><span class="w"> </span><span class="n">void</span><span class="w"> </span><span class="n">onSaveInstanceState</span><span class="p">(</span><span class="n">Bundle</span><span class="w"> </span><span class="n">outState</span><span class="p">)</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">super</span><span class="p">.</span><span class="n">onSaveInstanceState</span><span class="p">(</span><span class="n">outState</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">outState</span><span class="p">.</span><span class="n">putString</span><span class="p">(</span><span class="n">QUERYURL_KEY</span><span class="p">,</span><span class="w"> </span><span class="n">mUrlDisplayTextView</span><span class="p">.</span><span class="n">getText</span><span class="p">().</span><span class="n">toString</span><span class="p">());</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">outState</span><span class="p">.</span><span class="n">putString</span><span class="p">(</span><span class="n">RAW_JSON_KEY</span><span class="p">,</span><span class="w"> </span><span class="n">mSearchResultsTextView</span><span class="p">.</span><span class="n">getText</span><span class="p">().</span><span class="n">toString</span><span class="p">());</span><span class="w"></span></span>
<span class="code-line"><span class="err">}</span><span class="w"></span></span>
</pre></div>
<p>in <code>onCreate</code>: try to extract objects form bundle <code>savedInstanceState</code> (if it's not null). </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="err">@Override</span></span>
<span class="code-line"><span class="err">protected void onCreate(Bundle savedInstanceState) {</span></span>
<span class="code-line"><span class="err"> super.onCreate(savedInstanceState);</span></span>
<span class="code-line"><span class="err"> setContentView(R.layout.activity_main);</span></span>
<span class="code-line"><span class="err"> mSearchBoxEditText = (EditText) findViewById(R.id.et_search_box);</span></span>
<span class="code-line"><span class="err"> mUrlDisplayTextView = (TextView) findViewById(R.id.tv_url_display);</span></span>
<span class="code-line"><span class="err"> mSearchResultsTextView = (TextView) findViewById(R.id.tv_github_search_results_json);</span></span>
<span class="code-line"><span class="err"> mErrorMessageDisplay = (TextView) findViewById(R.id.tv_error_message_display);</span></span>
<span class="code-line"><span class="err"> mLoadingIndicator = (ProgressBar) findViewById(R.id.pb_loading_indicator);</span></span>
<span class="code-line"><span class="err"> // TODO (9) If the savedInstanceState bundle is not null, set the text of the URL and search results TextView respectively</span></span>
<span class="code-line"><span class="err"> if(savedInstanceState!=null && savedInstanceState.containsKey(QUERYURL_KEY))</span></span>
<span class="code-line"><span class="err"> mUrlDisplayTextView.setText(savedInstanceState.getString(QUERYURL_KEY));</span></span>
<span class="code-line"><span class="err"> if(savedInstanceState!=null && savedInstanceState.containsKey(RAW_JSON_KEY))</span></span>
<span class="code-line"><span class="err"> mSearchResultsTextView.setText(savedInstanceState.getString(RAW_JSON_KEY));</span></span>
<span class="code-line"><span class="err">}</span></span>
</pre></div>
<h2 id="asynctasks-and-loader">AsyncTasks and Loader</h2>
<p>edgecase: rotate when async task is performing → asynctask runs on separate thread → the zombie activities will not be killed !!
⇒ <code>Loader</code>
Loader is identified by a loader ID, thus preventing several loaders running in the same time.
<img alt="" class="img-responsive" src="../images/andev_p2e1_lifecycle/pasted_image002.png"/>
<code>AsyncTaskLoader</code> lifecycle:
it is bounded to an Activity instead of an async task ⇒ when device rotates, the loader will feed the results of tasks to the right activity. </p>
<p><img alt="" class="img-responsive" src="../images/andev_p2e1_lifecycle/pasted_image003.png"/></p>
<h2 id="using-loaders">Using Loaders</h2>
<ol>
<li>create loader id: <code>private static final GITHUB_SEARCH_LOADER = 22;</code></li>
<li>implement <code>LoaderCallbacks</code> interface functions in <code>MainActivity</code></li>
<li>init loader with a <code>LoaderManager</code>, and start the loader</li>
</ol>
<p>let <code>MainActivty</code> implement <code>LoaderManager.LoaderCallbacks<String></code></p>
<h3 id="implement-oncreateloader-onpreexecute-and-ondoinbackground-for-asynctask">implement onCreateLoader — onPreExecute and onDoInBackground for AsyncTask</h3>
<div class="highlight"><pre><span class="code-line"><span></span><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">3</span><span class="p">)</span><span class="w"> </span><span class="n">Override</span><span class="w"> </span><span class="n">onCreateLoader</span><span class="w"></span></span>
<span class="code-line"><span class="nv">@Override</span><span class="w"></span></span>
<span class="code-line"><span class="k">public</span><span class="w"> </span><span class="n">Loader</span><span class="o"><</span><span class="n">String</span><span class="o">></span><span class="w"> </span><span class="n">onCreateLoader</span><span class="p">(</span><span class="nc">int</span><span class="w"> </span><span class="n">id</span><span class="p">,</span><span class="w"> </span><span class="n">final</span><span class="w"> </span><span class="n">Bundle</span><span class="w"> </span><span class="n">bundle</span><span class="p">)</span><span class="w"> </span><span class="err">{</span><span class="o">//</span><span class="w"> </span><span class="err">!</span><span class="n">make</span><span class="w"> </span><span class="n">bundle</span><span class="w"> </span><span class="n">final</span><span class="w"> </span><span class="n">so</span><span class="w"> </span><span class="n">that</span><span class="w"> </span><span class="n">can</span><span class="w"> </span><span class="n">access</span><span class="w"> </span><span class="n">it</span><span class="w"> </span><span class="n">below</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">4</span><span class="p">)</span><span class="w"> </span><span class="k">Return</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">AsyncTaskLoader</span><span class="o"><</span><span class="n">String</span><span class="o">></span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="n">an</span><span class="w"> </span><span class="n">anonymous</span><span class="w"> </span><span class="k">inner</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">this</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="k">constructor</span><span class="s1">'s parameter</span></span>
<span class="code-line"><span class="s1"> return new AsyncTaskLoader<String>(this) {</span></span>
<span class="code-line"><span class="s1"> @Override</span></span>
<span class="code-line"><span class="s1"> public String loadInBackground() {</span></span>
<span class="code-line"><span class="s1"> return null;</span></span>
<span class="code-line"><span class="s1"> }</span></span>
<span class="code-line"><span class="s1"> // TODO (5) Override onStartLoading</span></span>
<span class="code-line"><span class="s1"> @Override</span></span>
<span class="code-line"><span class="s1"> protected void onStartLoading() {</span></span>
<span class="code-line"><span class="s1"> super.onStartLoading();</span></span>
<span class="code-line"><span class="s1"> // TODO (6) If bundle is null, return.</span></span>
<span class="code-line"><span class="s1"> if (bundle==null) return;</span></span>
<span class="code-line"><span class="s1"> // TODO (7) move the content of onPrecuter in the AsyncTask class</span></span>
<span class="code-line"><span class="s1"> mLoadingIndicator.setVisibility(View.VISIBLE);</span></span>
<span class="code-line"><span class="s1"> // TODO (8) Force a load</span></span>
<span class="code-line"><span class="s1"> forceLoad();</span></span>
<span class="code-line"><span class="s1"> }</span></span>
<span class="code-line"></span>
<span class="code-line"><span class="s1"> // TODO (9) Override loadInBackground</span></span>
<span class="code-line"><span class="s1"> @Override</span></span>
<span class="code-line"><span class="s1"> protected String onLoadInBackground() {</span></span>
<span class="code-line"><span class="s1"> // TODO (10) Get the String for our URL from the bundle passed to onCreateLoader</span></span>
<span class="code-line"><span class="s1"> String searchUrlstr= bundle.getString(SEARCH_QUERY_URL_EXTRA);</span></span>
<span class="code-line"><span class="s1"> // TODO (11) If the URL is null or empty, return null</span></span>
<span class="code-line"><span class="s1"> if(searchUrlstr==null || TextUtils.isEmpty(searchUrlstr)) return null;</span></span>
<span class="code-line"><span class="s1"> // TODO (12) Copy the try / catch block from the AsyncTask'</span><span class="n">s</span><span class="w"> </span><span class="n">doInBackground</span><span class="w"> </span><span class="k">method</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">githubSearchResults</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">null</span><span class="p">;</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="k">try</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">githubSearchResults</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">NetworkUtils</span><span class="p">.</span><span class="n">getResponseFromHttpUrl</span><span class="p">(</span><span class="k">new</span><span class="w"> </span><span class="n">URL</span><span class="p">(</span><span class="n">searchUrlstr</span><span class="p">));</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="err">}</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="p">(</span><span class="n">IOException</span><span class="w"> </span><span class="n">e</span><span class="p">)</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">e</span><span class="p">.</span><span class="n">printStackTrace</span><span class="p">();</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="err">}</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">githubSearchResults</span><span class="p">;</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="err">}</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="err">}</span><span class="p">;</span><span class="w"></span></span>
<span class="code-line"><span class="err">}</span><span class="w"></span></span>
</pre></div>
<h3 id="implement-onloadfinished-onpostexecute-for-asynctask">implement onLoadFinished — onPostExecute for AsyncTask</h3>
<div class="highlight"><pre><span class="code-line"><span></span><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">13</span><span class="p">)</span><span class="w"> </span><span class="n">Override</span><span class="w"> </span><span class="n">onLoadFinished</span><span class="w"></span></span>
<span class="code-line"><span class="nv">@Override</span><span class="w"></span></span>
<span class="code-line"><span class="k">public</span><span class="w"> </span><span class="n">void</span><span class="w"> </span><span class="n">onLoadFinished</span><span class="p">(</span><span class="n">Loader</span><span class="o"><</span><span class="n">String</span><span class="o">></span><span class="w"> </span><span class="n">loader</span><span class="p">,</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="n">githubSearchResults</span><span class="p">)</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">15</span><span class="p">)</span><span class="w"> </span><span class="k">Use</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">same</span><span class="w"> </span><span class="n">logic</span><span class="w"> </span><span class="n">used</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="n">onPostExecute</span><span class="w"> </span><span class="k">to</span><span class="w"> </span><span class="n">show</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="k">data</span><span class="w"> </span><span class="ow">or</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">error</span><span class="w"> </span><span class="n">message</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">mLoadingIndicator</span><span class="p">.</span><span class="n">setVisibility</span><span class="p">(</span><span class="k">View</span><span class="p">.</span><span class="n">INVISIBLE</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">githubSearchResults</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="k">null</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="err">!</span><span class="n">githubSearchResults</span><span class="p">.</span><span class="k">equals</span><span class="p">(</span><span class="ss">""</span><span class="p">))</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">showJsonDataView</span><span class="p">();</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">mSearchResultsTextView</span><span class="p">.</span><span class="n">setText</span><span class="p">(</span><span class="n">githubSearchResults</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="err">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">showErrorMessage</span><span class="p">();</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="err">}</span><span class="w"></span></span>
<span class="code-line"><span class="err">}</span><span class="w"></span></span>
<span class="code-line"></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">16</span><span class="p">)</span><span class="w"> </span><span class="n">Override</span><span class="w"> </span><span class="n">onLoaderReset</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="n">it</span><span class="w"> </span><span class="k">is</span><span class="w"> </span><span class="n">part</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">interface</span><span class="w"> </span><span class="n">we</span><span class="w"> </span><span class="n">implement</span><span class="p">,</span><span class="w"> </span><span class="n">but</span><span class="w"> </span><span class="n">don</span><span class="err">'</span><span class="n">t</span><span class="w"> </span><span class="n">do</span><span class="w"> </span><span class="n">anything</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="n">this</span><span class="w"> </span><span class="k">method</span><span class="w"></span></span>
<span class="code-line"><span class="nv">@Override</span><span class="w"></span></span>
<span class="code-line"><span class="k">public</span><span class="w"> </span><span class="n">void</span><span class="w"> </span><span class="n">onLoaderReset</span><span class="p">(</span><span class="n">Loader</span><span class="o"><</span><span class="n">String</span><span class="o">></span><span class="w"> </span><span class="n">loader</span><span class="p">)</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"></span>
<span class="code-line"><span class="err">}</span><span class="w"></span></span>
</pre></div>
<h3 id="in-makegithubsearchquery-create-bundle-create-a-loder-start-it">in makeGithubSearchQuery(): create bundle, create a loder, start it</h3>
<p>instead of staring an <code>AsyncTask</code>, we get a Loader and re-run it via a loader manager. </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="err">// TODO (19) Create a bundle called queryBundle</span></span>
<span class="code-line"><span class="err">Bundle queryBundle = new Bundle();</span></span>
<span class="code-line"><span class="err">// TODO (20) Use putString with SEARCH_QUERY_URL_EXTRA as the key and the String value of the URL as the value</span></span>
<span class="code-line"><span class="err">queryBundle.putString(SEARCH_QUERY_URL_EXTRA, githubSearchUrl.toString());</span></span>
<span class="code-line"><span class="err">// TODO (21) Call getSupportLoaderManager and store it in a LoaderManager variable</span></span>
<span class="code-line"><span class="err">LoaderManager loaderManager = getSupportLoaderManager();</span></span>
<span class="code-line"><span class="err">// TODO (22) Get our Loader by calling getLoader and passing the ID we specified</span></span>
<span class="code-line"><span class="err">Loader loader = loaderManager.getLoader(GITHUB_SEARCH_LOADER);</span></span>
<span class="code-line"><span class="err">// TODO (23) If the Loader was null, initialize it. Else, restart it.</span></span>
<span class="code-line"><span class="err">if(loader==null) loader = loaderManager.initLoader(GITHUB_SEARCH_LOADER, queryBundle, this);</span></span>
<span class="code-line"><span class="err">else loaderManager.restartLoader(GITHUB_SEARCH_LOADER, queryBundle, this);</span></span>
</pre></div>
<h2 id="caching-with-loaders_1">Caching with loaders</h2>
<p>Loaders will reload if activity is destroyed and re-created. This overhead can be avoided by caching the results in the <code>AsyncTaskLoader</code> (created in <code>onCreateLoader()</code>). </p>
<div class="highlight"><pre><span class="code-line"><span></span><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="k">Create</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="k">member</span><span class="w"> </span><span class="k">variable</span><span class="w"> </span><span class="k">called</span><span class="w"> </span><span class="n">mGithubJson</span><span class="w"> </span><span class="n">that</span><span class="w"> </span><span class="n">will</span><span class="w"> </span><span class="n">store</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="n">raw</span><span class="w"> </span><span class="n">JSON</span><span class="w"></span></span>
<span class="code-line"><span class="n">String</span><span class="w"> </span><span class="n">mGithubJson</span><span class="p">;</span><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="n">cached</span><span class="w"> </span><span class="n">results</span><span class="w"></span></span>
<span class="code-line"><span class="nv">@Override</span><span class="w"></span></span>
<span class="code-line"><span class="n">protected</span><span class="w"> </span><span class="n">void</span><span class="w"> </span><span class="n">onStartLoading</span><span class="p">()</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="cm">/* If no arguments were passed, we don't have a query to perform. Simply return. */</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">args</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="k">null</span><span class="p">)</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="k">return</span><span class="p">;</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="err">}</span><span class="w"></span></span>
<span class="code-line"></span>
<span class="code-line"><span class="w"> </span><span class="cm">/*</span></span>
<span class="code-line"><span class="cm"> * When we initially begin loading in the background, we want to display the</span></span>
<span class="code-line"><span class="cm"> * loading indicator to the user</span></span>
<span class="code-line"><span class="cm"> */</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">mLoadingIndicator</span><span class="p">.</span><span class="n">setVisibility</span><span class="p">(</span><span class="k">View</span><span class="p">.</span><span class="n">VISIBLE</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"></span>
<span class="code-line"><span class="w"> </span><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">2</span><span class="p">)</span><span class="w"> </span><span class="k">If</span><span class="w"> </span><span class="n">mGithubJson</span><span class="w"> </span><span class="k">is</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="k">null</span><span class="p">,</span><span class="w"> </span><span class="n">deliver</span><span class="w"> </span><span class="n">that</span><span class="w"> </span><span class="k">result</span><span class="p">.</span><span class="w"> </span><span class="n">Otherwise</span><span class="p">,</span><span class="w"> </span><span class="n">force</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="k">load</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="k">if</span><span class="p">(</span><span class="n">mGithubJson</span><span class="o">!=</span><span class="k">null</span><span class="p">)</span><span class="w"> </span><span class="n">deliverResult</span><span class="p">(</span><span class="n">mGithubJson</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="n">forceLoad</span><span class="p">();</span><span class="w"></span></span>
<span class="code-line"><span class="err">}</span><span class="w"></span></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">3</span><span class="p">)</span><span class="w"> </span><span class="n">Override</span><span class="w"> </span><span class="n">deliverResult</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="n">store</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="k">data</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="n">mGithubJson</span><span class="w"></span></span>
<span class="code-line"><span class="nv">@Override</span><span class="w"></span></span>
<span class="code-line"><span class="k">public</span><span class="w"> </span><span class="n">void</span><span class="w"> </span><span class="n">deliverResult</span><span class="p">(</span><span class="n">String</span><span class="w"> </span><span class="k">data</span><span class="p">)</span><span class="w"> </span><span class="err">{</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">mGithubJson</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">data</span><span class="p">;</span><span class="w"></span></span>
<span class="code-line"><span class="o">//</span><span class="w"> </span><span class="n">TODO</span><span class="w"> </span><span class="p">(</span><span class="mi">4</span><span class="p">)</span><span class="w"> </span><span class="k">Call</span><span class="w"> </span><span class="n">super</span><span class="p">.</span><span class="n">deliverResult</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="n">storing</span><span class="w"> </span><span class="n">the</span><span class="w"> </span><span class="k">data</span><span class="w"></span></span>
<span class="code-line"><span class="w"> </span><span class="n">super</span><span class="p">.</span><span class="n">deliverResult</span><span class="p">(</span><span class="k">data</span><span class="p">);</span><span class="w"></span></span>
<span class="code-line"><span class="err">}</span><span class="w"></span></span>
</pre></div>
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<div id="toc"><ul><li><a class="toc-href" href="#onsavedinstancestate" title="onSavedInstanceState()">onSavedInstanceState()</a></li><li><a class="toc-href" href="#asynctasks-and-loader" title="AsyncTasks and Loader">AsyncTasks and Loader</a></li><li><a class="toc-href" href="#using-loaders" title="Using Loaders">Using Loaders</a><ul><li><a class="toc-href" href="#implement-oncreateloader-onpreexecute-and-ondoinbackground-for-asynctask" title="implement onCreateLoader — onPreExecute and onDoInBackground for AsyncTask">implement onCreateLoader — onPreExecute and onDoInBackground for AsyncTask</a></li><li><a class="toc-href" href="#implement-onloadfinished-onpostexecute-for-asynctask" title="implement onLoadFinished — onPostExecute for AsyncTask">implement onLoadFinished — onPostExecute for AsyncTask</a></li><li><a class="toc-href" href="#in-makegithubsearchquery-create-bundle-create-a-loder-start-it" title="in makeGithubSearchQuery(): create bundle, create a loder, start it">in makeGithubSearchQuery(): create bundle, create a loder, start it</a></li></ul></li><li><a class="toc-href" href="#caching-with-loaders_1" title="Caching with loaders">Caching with loaders</a></li></ul></div>
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