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copied!<blockquote> <p>Why can't it be the onResume() is invoked after onRestart() and onCreate() methods just excluding onStart()? What is its purpose?</p> </blockquote> <p>OK, as my first answer was pretty long I won't extend it further so let's try this...</p> <pre><code>public DriveToWorkActivity extends Activity implements onReachedGroceryStoreListener { } public GroceryStoreActivity extends Activity {} </code></pre> <p><strong>PLEASE NOTE:</strong> I've deliberately left out the calls to things like <code>super.onCreate(...)</code> etc. This is pseudo-code so give me some artistic licence here. ;)</p> <p>The methods for <code>DriveToWorkActivity</code> follow...</p> <pre><code>protected void onCreate(...) { openGarageDoor(); unlockCarAndGetIn(); closeCarDoorAndPutOnSeatBelt(); putKeyInIgnition(); } protected void onStart() { startEngine(); changeRadioStation(); switchOnLightsIfNeeded(); switchOnWipersIfNeeded(); } protected void onResume() { applyFootbrake(); releaseHandbrake(); putCarInGear(); drive(); } protected void onPause() { putCarInNeutral(); applyHandbrake(); } protected void onStop() { switchEveryThingOff(); turnOffEngine(); removeSeatBeltAndGetOutOfCar(); lockCar(); } protected void onDestroy() { enterOfficeBuilding(); } protected void onReachedGroceryStore(...) { Intent i = new Intent(ACTION_GET_GROCERIES, ..., this, GroceryStoreActivity.class); } protected void onRestart() { unlockCarAndGetIn(); closeDoorAndPutOnSeatBelt(); putKeyInIgnition(); } </code></pre> <p>OK, so it's another long one (sorry folks). But here's my explanation...</p> <p><code>onResume()</code> is when I start driving and <code>onPause()</code> is when I come to a temporary stop. So I drive then reach a red light so I pause...the light goes green and I resume. Another red light and I pause, then green so I resume. The <code>onPause() -> onResume() -> onPause() -> onResume()</code> loop is a tight one and occurs many times through my journey.</p> <p>The loop from being stopped back through a restart (preparing to carry on my journey) to starting again is perhaps less common. In one case, I spot the Grocery Store and the <code>GroceryStoreActivity</code> is started (forcing my <code>DriveToWorkActivity</code> to the point of <code>onStop()</code>). When I return from the store, I go through <code>onRestart()</code> and <code>onStart()</code> then resume my journey.</p> <p>I could put the code that's in <code>onStart()</code> into both <code>onCreate()</code> and <code>onRestart()</code> and not bother to override <code>onStart()</code> at all but the more that needs to be done between <code>onCreate() -> onResume()</code> and <code>onRestart() -> onResume()</code>, the more I'm duplicating things.</p> <p>So, to requote once more...</p> <blockquote> <p>Why can't it be the onResume() is invoked after onRestart() and onCreate() methods just excluding onStart()?</p> </blockquote> <p>If you don't override <code>onStart()</code> then this is effectively what happens. Although the <code>onStart()</code> method of <code>Activity</code> will be called implicitly, the effect in your code is effectively <code>onCreate() -> onResume()</code> or <code>onRestart() -> onResume()</code>.</p>

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