Dialog是任何系统都必须有的一个控件，作为辅助窗口，用于显示一些消息，或请求用户采取一引起操作等。

在Android中也不例外，基本使用可能参看文档。

使用时的注意事项1. BACK键能取消掉对话框(dismiss)，但是却不会触发其onOkey和onCancel回调接口，所以如果你的对话框会改某些状态，一定要注意还有第三种方式取消对话框。

2. 尽量少用模态对话框(Model dialog)，如果Dialog.setCancellable(false)，就变成了一个模态对话框，除了程序内部把其Dismiss，否则按什么键都无法将其取消。这是极差的用户体验，对话框本身就是一种干扰，再无法取消会把用户搞疯的。所以除非特别有必要，也即当执行某个操作时不希望被打破，才可以使用模态对话框。

3. 尽量少用对话框，它对用户是一种干扰，除非需要用户做操作，或者做出选择。通常的一般性的通知用Toast或者Notification就足够了。

4. 不要使用对话框风格的Activity，也即把Activity变成一个对话框。因为这样是自已定义的布局，与系统Dialog的风格可能会不一致。最严重的是当系统风格发生变化，Dialog的子类会变化，但Activity式的对话框就不会变化。可以在ICS中找一找Activity对话框，你会发现其OK是在左边，而ICS中系统Dialog的OK都是在右边的。

5. 尽量保证Dialog对象活在Activity的生命周期之内，也即至多是在onCreate()和onDestroy()之间。

6. 要想到和测试到Activity在其Dialog.dismiss()之前死掉的情况。因为Activity必须依附于某个正在显示的Activity实例，当显示和取消的时候其Activity实例必须存在，否则就会有"IllegalArgumentException: View not attached to window manager"。

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()必须在主线程里调用，但Dialog.dismiss()却可以在任何线程中调用。

三种使用方式比较1. 直接创建一个局部的Dialog对象

优点是变量是局部的容易理解和维护。缺点是Dialog对象难以控制，容易引发RuntimeException。

2. 把Dialog对象变成Activity的域

优点是Dialog对象可以重复利用，且Activity可以控制以保证Dialog不会在Activity生命周期外显示。是推荐的使用方式。

3. 用Activity的方法onCreateDialog(), showDialog()和dismissDialog()

优点是Frameworks会帮忙照看Dialog，在大多数情况下这是推荐的做法。但是对于Activity提前死掉的情况，此方法必有RuntimeException，且无法回避。

实例

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.

}

}