Android 双击返回键功能
的有关信息介绍如下：
android连续点击两次返回键退出应用，一般大家都是使用时间差来实现功能，现在来看下Handler机制简单实现方式
编写双击返回工具类DoubleClickExitHelper
public class DoubleClickExitHelper {
private final Activity mActivity;
private boolean isOnKeyBacking;
private Handler mHandler;
private Toast mBackToast;
public DoubleClickExitHelper(Activity activity) {
mActivity = activity;
mHandler = new Handler(Looper.getMainLooper());
}
/**
* Activity onKeyDown事件
* */
public boolean onKeyDown(int keyCode, KeyEvent event) {
if(keyCode != KeyEvent.KEYCODE_BACK) {
return false;
}
if(isOnKeyBacking) {
mHandler.removeCallbacks(onBackTimeRunnable);
if(mBackToast != null){
mBackToast.cancel();
}
mActivity.finish();
return true;
} else {
isOnKeyBacking = true;
if(mBackToast == null) {
mBackToast = Toast.makeText(mActivity, "再按一次返回", 2000);
}
mBackToast.show();
//延迟两秒的时间，把Runable发出去
mHandler.postDelayed(onBackTimeRunnable, 2000);
return true;
}
}
private Runnable onBackTimeRunnable = new Runnable() {
@Override
public void run() {
isOnKeyBacking = false;
if(mBackToast != null){
mBackToast.cancel();
}
}
};
}
在我们需要的Activity类中初始化DoubleClickExitHelper：
DoubleClickExitHelper doubleClick = new DoubleClickExitHelper(this);
重写OnKeyDown():
/**
* Returns:
* Return
* true to prevent this event from being propagated further, or false to
* indicate that you have not handled this event and it should continue to
* be propagated.
*/
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (event.getKeyCode() == KeyEvent.KEYCODE_BACK) {
//在此可以调用
return doubleClick.onKeyDown(keyCode, event);
}
return super.onKeyDown(keyCode, event);
}
已完成，大家可以试试
当然在Android2.0后已经新增了onBackPressed（）；
/**
* Called when a key was pressed down and not handled by any of the views
* inside of the activity. So, for example, key presses while the cursor
* is inside a TextView will not trigger the event (unless it is a navigation
* to another object) because TextView handles its own key presses.
*
*
If the focused view didn't want this event, this method is called.
*
*
The default implementation takes care of {@link KeyEvent#KEYCODE_BACK}
* by calling {@link #onBackPressed()}, though the behavior varies based
* on the application compatibility mode: for
* {@link android.os.Build.VERSION_CODES#ECLAIR} or later applications,
* it will set up the dispatch to call {@link #onKeyUp} where the action
* will be performed; for earlier applications, it will perform the
* action immediately in on-down, as those versions of the platform
* behaved.
*
*
Other additional default key handling may be performed
* if configured with {@link #setDefaultKeyMode}.
*
* @return Return true to prevent this event from being propagated
* further, or false to indicate that you have not handled
* this event and it should continue to be propagated.
* @see #onKeyUp
* @see android.view.KeyEvent
*/
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
if (getApplicationInfo().targetSdkVersion
>= Build.VERSION_CODES.ECLAIR) {
event.startTracking();
} else {
onBackPressed();
}
return true;
}
if (mDefaultKeyMode == DEFAULT_KEYS_DISABLE) {
return false;
} else if (mDefaultKeyMode == DEFAULT_KEYS_SHORTCUT) {
if (getWindow().performPanelShortcut(Window.FEATURE_OPTIONS_PANEL,
keyCode, event, Menu.FLAG_ALWAYS_PERFORM_CLOSE)) {
return true;
}
return false;
} else {
// Common code for DEFAULT_KEYS_DIALER & DEFAULT_KEYS_SEARCH_*
boolean clearSpannable = false;
boolean handled;
if ((event.getRepeatCount() != 0) || event.isSystem()) {
clearSpannable = true;
handled = false;
} else {
handled = TextKeyListener.getInstance().onKeyDown(
null, mDefaultKeySsb, keyCode, event);
if (handled && mDefaultKeySsb.length() > 0) {
// something useable has been typed - dispatch it now.
final String str = mDefaultKeySsb.toString();
clearSpannable = true;
switch (mDefaultKeyMode) {
case DEFAULT_KEYS_DIALER:
Intent intent = new Intent(Intent.ACTION_DIAL, Uri.parse("tel:" + str));
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);
break;
case DEFAULT_KEYS_SEARCH_LOCAL:
startSearch(str, false, null, false);
break;
case DEFAULT_KEYS_SEARCH_GLOBAL:
startSearch(str, false, null, true);
break;
}
}
}
if (clearSpannable) {
mDefaultKeySsb.clear();
mDefaultKeySsb.clearSpans();
Selection.setSelection(mDefaultKeySsb,0);
}
return handled;
}
}
