Android開發筆記之:Dialog的使用詳解

Dialog是任何系統都必須有的一個控件，作為輔助窗口，用於顯示一些消息，或請求用戶采取一引起操作等。
在Android中也不例外，基本使用可能參看文檔。
使用時的注意事項
1. BACK鍵能取消掉對話框(dismiss)，但是卻不會觸發其onOkey和onCancel回調接口，所以如果你的對話框會改某些狀態，一定要注意還有第三種方式取消對話框。
2. 盡量少用模態對話框(Model dialog)，如果Dialog.setCancellable(false)，就變成了一個模態對話框，除了程序內部把其Dismiss，否則按什麼鍵都無法將其取消。這是極差的用戶體驗，對話框本身就是一種干擾，再無法取消會把用戶搞瘋的。所以除非特別有必要，也即當執行某個操作時不希望被打破，才可以使用模態對話框。
3. 盡量少用對話框，它對用戶是一種干擾，除非需要用戶做操作，或者做出選擇。通常的一般性的通知用Toast或者Notification就足夠了。
4. 不要使用對話框風格的Activity，也即把Activity變成一個對話框。因為這樣是自已定義的布局，與系統Dialog的風格可能會不一致。最嚴重的是當系統風格發生變化，Dialog的子類會變化，但Activity式的對話框就不會變化。可以在ICS中找一找Activity對話框，你會發現其OK是在左邊，而ICS中系統Dialog的OK都是在右邊的。
5. 盡量保證Dialog對象活在Activity的生命周期之內，也即至多是在onCreate()和onDestroy()之間。
6. 要想到和測試到Activity在其Dialog.dismiss()之前死掉的情況。因為Activity必須依附於某個正在顯示的Activity實例，當顯示和取消的時候其Activity實例必須存在，否則就會有"IllegalArgumentException: View not attached to window manager"。
復制代碼 代碼如下:
05-15 02:45:26.320: E/AndroidRuntime(1161): java.lang.IllegalArgumentException: View not attached to window manager
05-15 02:45:26.320: E/AndroidRuntime(1161):     at android.view.WindowManagerImpl.findViewLocked(WindowManagerImpl.java:355)
05-15 02:45:26.320: E/AndroidRuntime(1161):     at android.view.WindowManagerImpl.removeView(WindowManagerImpl.java:200)
05-15 02:45:26.320: E/AndroidRuntime(1161):     at android.view.Window$LocalWindowManager.removeView(Window.java:432)
05-15 02:45:26.320: E/AndroidRuntime(1161):     at android.app.Dialog.dismissDialog(Dialog.java:278)
05-15 02:45:26.320: E/AndroidRuntime(1161):     at android.app.Dialog.access$000(Dialog.java:71)
05-15 02:45:26.320: E/AndroidRuntime(1161):     at android.app.Dialog$1.run(Dialog.java:111)
05-15 02:45:26.320: E/AndroidRuntime(1161):     at android.app.Dialog.dismiss(Dialog.java:268)
05-15 02:45:26.320: E/AndroidRuntime(1161):     at com.hilton.effectiveandroid.app.DialogDemo$1.handleMessage(DialogDemo.java:26)
05-15 02:45:26.320: E/AndroidRuntime(1161):     at android.os.Handler.dispatchMessage(Handler.java:99)

7. Dialog.show()必須在主線程裡調用，但Dialog.dismiss()卻可以在任何線程中調用。
三種使用方式比較
1. 直接創建一個局部的Dialog對象
優點是變量是局部的容易理解和維護。缺點是Dialog對象難以控制，容易引發RuntimeException。
2. 把Dialog對象變成Activity的域
優點是Dialog對象可以重復利用，且Activity可以控制以保證Dialog不會在Activity生命周期外顯示。是推薦的使用方式。
3. 用Activity的方法onCreateDialog(), showDialog()和dismissDialog()
優點是Frameworks會幫忙照看Dialog，在大多數情況下這是推薦的做法。但是對於Activity提前死掉的情況，此方法必有RuntimeException，且無法回避。
實例
復制代碼 代碼如下:
public class DialogDemo extends Activity {
    private static final int DISMISS_DIALOG = 1;

    private ProgressDialog mBetterDialog;
    private Handler mMainHandler = new Handler() {
 @Override
 public void handleMessage(Message msg) {
     switch (msg.what) {
     case DISMISS_DIALOG:
  Dialog dialog = (Dialog) msg.obj;
  dialog.dismiss();
  break;
     default:
  break;
     }
 }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.dialog_demo);

 final Button sucking = (Button) findViewById(R.id.sucking);
 sucking.setOnClickListener(new View.OnClickListener() {
     public void onClick(View v) {
  final Activity activity = DialogDemo.this;
  final ProgressDialog dialog = new ProgressDialog(activity);
  dialog.setTitle("Worst dialogging");
  dialog.setMessage("This is the worst dialogging scheme, NEVER use it. This dialog is easy to " +
   "run out of its attached activity, yielding WindowManager#BadTokenException if the activity is gone when dismissing");
  dialog.setIndeterminate(true);
  dialog.setCancelable(true);
  // You MUST do the show in main thread anyway
  dialog.show();
  new Thread(new Runnable() {
      public void run() {
   SystemClock.sleep(10000);
   /*
    * IllegalArgumentException: View not attached to window manager
    * If the activity showing the dialog was killed before dismiss() out of rotation or locale changed,
    * the dialog will gone with activity, but when dismiss() yields "IllegalArgumentException: View not attached to
    * window manager".
    * Checking isShowing() won't help.
    * Checking activity.isFinishing() won't help, either.
    * Dismiss it in main thread also won't give any help.
    */
   // THIS WON't WORK
//   if (dialog.isShowing()) {
//       dialog.dismiss();
//   }
//   if (!activity.isFinishing()) {
//       dialog.dismiss();
//   }
   Message msg = Message.obtain();
   msg.what = DISMISS_DIALOG;
   msg.obj = dialog;
   mMainHandler.sendMessage(msg);
      }
  }).start();
     }
 });

 final Button better = (Button) findViewById(R.id.better);
 better.setOnClickListener(new View.OnClickListener() {
     public void onClick(View v) {
  mBetterDialog = new ProgressDialog(DialogDemo.this);
  mBetterDialog.setTitle("Better dialogging");
  mBetterDialog.setMessage("This dialogging can be used. The dialog object is a field of its activity, so activity can" +
    " control it to make sure dialog only lives within activity lifecircle");
  mBetterDialog.setIndeterminate(true);
  mBetterDialog.setCancelable(true);
  // You MUST do the show in main thread anyway
  mBetterDialog.show();
  new Thread(new Runnable() {
      public void run() {
   SystemClock.sleep(10000);
   /*
    * This is much better, mBetterDialog is a field of its activity, so activity can take care of it in order
    * to make sure dialog only live within activity's life circle, to avoid any unexpected exceptions.
    */
   // THIS really works
       if (mBetterDialog != null && mBetterDialog.isShowing()) {
           mBetterDialog.dismiss();
       }
      }
  }).start();
     }
 });

 final Button optional = (Button) findViewById(R.id.optional);
 optional.setOnClickListener(new View.OnClickListener() {
     @SuppressWarnings("deprecation")
     public void onClick(View v) {
  showDialog(0);
  new Thread(new Runnable() {
      public void run() {
   SystemClock.sleep(10000);
   /*
    * This way works best for most of time, except if activity died before dismissing, exception must be
    * thrown: "IllegalArgumentException: View not attached to window manager".
    * Although activity takes care of its belonging dialog, there is no way to operate it manually any more.
    * First you do not have reference to dialog object and second, any manual operation only interferences
    * and breaks state maintained by frameworks.
    */
   dismissDialog(0);
      }
  }).start();
     }
 });
    }
    @Override
    protected Dialog onCreateDialog(int id) {
 ProgressDialog d = new ProgressDialog(this);
 d.setTitle("Optional dialogging");
 d.setMessage("This dialogging scheme works best for most times, the dialogs are all taken care of by activitys and frameworks" +
   ". Except for activity being killed during dialog showing");
 d.setIndeterminate(true);
 d.setCancelable(true);
 return d;
    }
    @Override
    protected void onDestroy() {
 super.onDestroy();
 // Activity is dying, all its belonging dialogs should be dismissed, of course.
 if (mBetterDialog != null && mBetterDialog.isShowing()) {
     mBetterDialog.dismiss();
     mBetterDialog = null;
 }
 // For dialogs showed via showDialog(int), no way to stop it in onDestroy()
// dismissDialog(0); // cause "IllegalArgumentException: no dialog with id 0 was ever shown via Activity#showDialog"
       // This is because Activity has to manage its dialog during onPause() and onResume() to restore
                   // dialogs' state. So if you manually dismiss it in onDestroy(), it will cause JE.

// removeDialog(0);// cause "IllegalArgumentException: no dialog with id 0 was ever shown via Activity#showDialog", when
   // dismissing in thread.
               // This is because Activity has to manage its dialog during onPause() and onResume() to restore
                     // dialogs' state. So if you manually dismiss it in onDestroy(), it will cause JE.
    }
}