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.
}
}
