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Diffstat (limited to 'docs/html/guide/topics/views/ui-events.jd')
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1 files changed, 88 insertions, 6 deletions
diff --git a/docs/html/guide/topics/views/ui-events.jd b/docs/html/guide/topics/views/ui-events.jd index 4230314..96136f8 100644 --- a/docs/html/guide/topics/views/ui-events.jd +++ b/docs/html/guide/topics/views/ui-events.jd @@ -1,13 +1,37 @@ page.title=Handling UI Events +parent.title=Views and Layout +parent.link=index.html @jd:body -<p>Many Android classes declare callback methods for handling relevant UI events such as keypresses, touch events, focus changes, and so on. For example, {@link android.app.Activity Activity} provides the methods onKeyDown() and onKeyUp() and {@link android.widget.TextView TextView} provides onFocusChanged(). </p> +<div id="qv-wrapper"> +<div id="qv"> + <h2>In this document</h2> + <ol> + <li><a href="#TouchMode">Touch Mode</a></li> + <li><a href="#Scrolling">Scrolling</a></li> + <li><a href="#EventCycle">Event Cycle</a></li> + </ol> -<p>In most cases, you can handle events just by overriding the appropriate handler methods. When an event is received, the Android system calls your handler method with the event data.</p> + <h2>See also</h2> + <ol> + <li><a href="{@docRoot}guide/tutorials/views/hello-formstuff.html">Hello Form Stuff tutorial</a></li> + </ol> +</div> +</div> -<p>However, some classes do not declare handler methods for specific events. For example, {@link android.widget.Button Button} does not declare an onClick() handler method. To handle such events, you need to create an anonymous class to act as a listener for the event, then register the listener with the target class object. The example below shows how to set up a handler for click events in a Button object. </p> +<p>Many Android classes declare callback methods for handling relevant UI events such as keypresses, +touch events, focus changes, and so on. For example, {@link android.app.Activity Activity} provides +the methods <code>onKeyDown()</code> and <code>onKeyUp()</code> and {@link android.widget.TextView TextView} +provides <code>onFocusChanged()</code>. </p> +<p>In most cases, you can handle events just by overriding the appropriate handler methods. +When an event is received, the Android system calls your handler method with the event data.</p> +<p>However, some classes do not declare handler methods for specific events. For example, +{@link android.widget.Button} does not declare an <code>onClick()</code> handler method. So, to handle a click event, +you need to create an anonymous class to act as a listener for the event, then register the listener with the +target class object (via the appropriate <code>set...Listener()</code> method). The example below shows how to set +up a handler for click events in a Button object. </p> </p> <pre>public class ExampleSendResult extends Activity @@ -16,7 +40,7 @@ page.title=Handling UI Events { ... - // Listen for button clicks. + // Capture our button from layout and listen for clicks. Button button = (Button)findViewById(R.id.corky); button.setOnClickListener(mCorkyListener); } @@ -26,6 +50,64 @@ page.title=Handling UI Events { public void onClick(View v) { - //handle click event... + //do something when the button is clicked } - };</pre> + }; +} +</pre> + + +<h2 id="TouchMode">Touch Mode</h2> + <p> + When a user is navigating a user interface via directional keys such as a D-pad, it is + necessary to give focus to actionable items such as buttons so the user can see + what will take input. If the device has touch capabilities, however, and the user + begins interacting with the interface by touching it, it is no longer necessary to + always highlight, or give focus to, a particular view. Thus, there is a mode + for interaction named "touch mode." + </p> + <p> + For a touch-capable device, once the user touches the screen, the device + will enter touch mode. From this point onward, only views for which + {@link android.view.View#isFocusableInTouchMode} is true will be focusable, such as text editing widgets. + Other views that are touchable, like buttons, will not take focus when touched; they will + simply fire their on-click listeners when pressed. + </p> + <p> + Any time a user hits a directional key, such as a D-pad direction, the view device will + exit touch mode, and find a view to take focus, so that the user may resume interacting + with the user interface without touching the screen. + </p> + <p> + The touch mode state is maintained across {@link android.app.Activity}s. To query the current state, you can call + {@link android.view.View#isInTouchMode} to see whether the device is currently in touch mode. + </p> + + +<h2 id="Scrolling">Scrolling</h2> + <p> + The framework provides basic support for views that wish to internally + scroll their content. This includes keeping track of the X and Y scroll + offset as well as mechanisms for drawing scrollbars. See + {@link android.view.View#scrollBy(int, int)}, {@link android.view.View#scrollTo(int, int)} for more details. + </p> + +<h2 is="EventCycle">Event Cycle</h2> + <p>The basic cycle of a view is as follows:</p> + <ol> + <li>An event comes in and is dispatched to the appropriate view. The view + handles the event and notifies any listeners.</li> + <li>If, in the course of processing the event, the view's bounds may need + to be changed, the view will call {@link android.view.View#requestLayout()}.</li> + <li>Similarly, if in the course of processing the event the view's appearance + may need to be changed, the view will call {@link android.view.View#invalidate()}.</li> + <li>If either {@link android.view.View#requestLayout()} or {@link android.view.View#invalidate()} were called, + the framework will take care of measuring, laying out, and drawing the tree + as appropriate.</li> + </ol> + + <p class="note"><strong>Note:</strong> The entire view tree is single threaded. You must always be on + the UI thread when calling any method on any view. + If you are doing work on other threads and want to update the state of a view + from that thread, you should use a {@link android.os.Handler}. + </p>
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