我的程序在后台线程中执行一些网络活动。在开始之前,它会弹出一个进度对话框。该对话框在处理程序上被解除。这一切都很好,除了当对话框打开时屏幕方向发生变化(背景线程正在运行)。此时,应用程序要么崩溃,要么死锁,要么进入一个奇怪的阶段,在所有线程被杀死之前,应用程序根本无法工作。
我如何处理屏幕方向的变化优雅?
下面的示例代码大致匹配我的实际程序:
public class MyAct extends Activity implements Runnable {
public ProgressDialog mProgress;
// UI has a button that when pressed calls send
public void send() {
mProgress = ProgressDialog.show(this, "Please wait",
"Please wait",
true, true);
Thread thread = new Thread(this);
thread.start();
}
public void run() {
Thread.sleep(10000);
Message msg = new Message();
mHandler.sendMessage(msg);
}
private final Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
mProgress.dismiss();
}
};
}
栈:
E/WindowManager( 244): Activity MyAct has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@433b7150 that was originally added here
E/WindowManager( 244): android.view.WindowLeaked: Activity MyAct has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@433b7150 that was originally added here
E/WindowManager( 244): at android.view.ViewRoot.<init>(ViewRoot.java:178)
E/WindowManager( 244): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:147)
E/WindowManager( 244): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:90)
E/WindowManager( 244): at android.view.Window$LocalWindowManager.addView(Window.java:393)
E/WindowManager( 244): at android.app.Dialog.show(Dialog.java:212)
E/WindowManager( 244): at android.app.ProgressDialog.show(ProgressDialog.java:103)
E/WindowManager( 244): at android.app.ProgressDialog.show(ProgressDialog.java:91)
E/WindowManager( 244): at MyAct.send(MyAct.java:294)
E/WindowManager( 244): at MyAct$4.onClick(MyAct.java:174)
E/WindowManager( 244): at android.view.View.performClick(View.java:2129)
E/WindowManager( 244): at android.view.View.onTouchEvent(View.java:3543)
E/WindowManager( 244): at android.widget.TextView.onTouchEvent(TextView.java:4664)
E/WindowManager( 244): at android.view.View.dispatchTouchEvent(View.java:3198)
我已经尝试在onSaveInstanceState中取消进度对话框,但这只是防止了立即崩溃。背景线程仍在运行,UI处于部分绘制状态。需要在它重新开始工作之前杀死整个应用程序。
如果你维护两个布局,所有的UI线程都应该终止。
如果你使用AsynTask,那么你可以很容易地在当前活动的onDestroy()方法中调用.cancel()方法。
@Override
protected void onDestroy (){
removeDialog(DIALOG_LOGIN_ID); // remove loading dialog
if (loginTask != null){
if (loginTask.getStatus() != AsyncTask.Status.FINISHED)
loginTask.cancel(true); //cancel AsyncTask
}
super.onDestroy();
}
对于AsyncTask,请在“取消任务”部分阅读更多信息。
更新:
增加了检查状态的条件,因为只有当它处于运行状态时才能取消。
还要注意,AsyncTask只能执行一次。
如今,有一种更加独特的方式来处理这类问题。典型的方法是:
1. 确保你的数据与用户界面正确分离:
任何后台进程都应该在一个保留的Fragment中(使用Fragment. setretaininstance()设置此值)。这就成为了你的“持久数据存储”,你想要保留的任何数据都会被保留。在方向改变事件之后,这个片段仍然可以通过FragmentManager.findFragmentByTag()调用以其原始状态访问(当你创建它时,你应该给它一个标签而不是一个ID,因为它没有附加到一个视图)。
请参阅处理运行时更改开发指南,了解如何正确执行此操作,以及为什么这是最佳选择。
2. 确保你在后台进程和你的UI之间正确和安全的接口:
You must reverse your linking process. At the moment your background process attaches itself to a View - instead your View should be attaching itself to the background process. It makes more sense right? The View's action is dependent on the background process, whereas the background process is not dependent on the View.This means changing the link to a standard Listener interface. Say your process (whatever class it is - whether it is an AsyncTask, Runnable or whatever) defines a OnProcessFinishedListener, when the process is done it should call that listener if it exists.
这个答案很好地简洁地描述了如何定制侦听器。
3.每当UI被创建(包括方向的改变)时,将你的UI链接到数据过程中:
现在你必须考虑如何将后台任务与当前View结构连接起来。如果你正确地处理了你的方向变化(而不是人们经常推荐的configChanges黑客),那么你的对话框将被系统重新创建。这很重要,它意味着在方向改变时,所有Dialog的生命周期方法都会被召回。所以在这些方法中(onCreateDialog通常是一个好地方),你可以像下面这样调用:
DataFragment f = getActivity().getFragmentManager().findFragmentByTag("BACKGROUND_TAG");
if (f != null) {
f.mBackgroundProcess.setOnProcessFinishedListener(new OnProcessFinishedListener() {
public void onProcessFinished() {
dismiss();
}
});
}
查看Fragment生命周期以确定侦听器的设置最适合于您的个人实现。
这是一种通用方法,用于为本问题中问到的一般问题提供健壮而完整的解决方案。根据您的具体情况,这个答案中可能还缺少一些细节,但这通常是正确处理方向更改事件的最正确方法。
我的解决方案是扩展ProgressDialog类来获得我自己的MyProgressDialog。
我重新定义了show()和dismiss()方法来在显示对话框之前锁定方向,并在对话框被解散时将其解锁。
因此,当显示对话框并且设备的方向发生变化时,屏幕的方向保持不变,直到调用dismiss(),然后屏幕方向根据传感器值/设备方向发生变化。
这是我的代码:
public class MyProgressDialog extends ProgressDialog {
private Context mContext;
public MyProgressDialog(Context context) {
super(context);
mContext = context;
}
public MyProgressDialog(Context context, int theme) {
super(context, theme);
mContext = context;
}
public void show() {
if (mContext.getResources().getConfiguration().orientation == Configuration.ORIENTATION_PORTRAIT)
((Activity) mContext).setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
else
((Activity) mContext).setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
super.show();
}
public void dismiss() {
super.dismiss();
((Activity) mContext).setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_SENSOR);
}
}
我尝试执行jfelectron的解决方案,因为它是“解决这些问题的坚如磐石的解决方案,符合‘Android方式’”,但我花了一些时间来查找并整合所有提到的元素。最终得到了这个略有不同的,我认为更优雅的解决方案,完整地贴在这里。
使用从活动中触发的IntentService在单独的线程上执行长时间运行的任务。该服务向更新对话框的活动发出sticky Broadcast intent。Activity使用showDialog(), onCreateDialog()和onPrepareDialog()来消除在应用程序对象或savedInstanceState包中传递持久化数据的需要。无论应用程序如何中断,这都应该工作。
活动类:
public class TesterActivity extends Activity {
private ProgressDialog mProgressDialog;
private static final int PROGRESS_DIALOG = 0;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button b = (Button) this.findViewById(R.id.test_button);
b.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
buttonClick();
}
});
}
private void buttonClick(){
clearPriorBroadcast();
showDialog(PROGRESS_DIALOG);
Intent svc = new Intent(this, MyService.class);
startService(svc);
}
protected Dialog onCreateDialog(int id) {
switch(id) {
case PROGRESS_DIALOG:
mProgressDialog = new ProgressDialog(TesterActivity.this);
mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
mProgressDialog.setMax(MyService.MAX_COUNTER);
mProgressDialog.setMessage("Processing...");
return mProgressDialog;
default:
return null;
}
}
@Override
protected void onPrepareDialog(int id, Dialog dialog) {
switch(id) {
case PROGRESS_DIALOG:
// setup a broadcast receiver to receive update events from the long running process
IntentFilter filter = new IntentFilter();
filter.addAction(MyService.BG_PROCESS_INTENT);
registerReceiver(new MyBroadcastReceiver(), filter);
break;
}
}
public class MyBroadcastReceiver extends BroadcastReceiver{
@Override
public void onReceive(Context context, Intent intent) {
if (intent.hasExtra(MyService.KEY_COUNTER)){
int count = intent.getIntExtra(MyService.KEY_COUNTER, 0);
mProgressDialog.setProgress(count);
if (count >= MyService.MAX_COUNTER){
dismissDialog(PROGRESS_DIALOG);
}
}
}
}
/*
* Sticky broadcasts persist and any prior broadcast will trigger in the
* broadcast receiver as soon as it is registered.
* To clear any prior broadcast this code sends a blank broadcast to clear
* the last sticky broadcast.
* This broadcast has no extras it will be ignored in the broadcast receiver
* setup in onPrepareDialog()
*/
private void clearPriorBroadcast(){
Intent broadcastIntent = new Intent();
broadcastIntent.setAction(MyService.BG_PROCESS_INTENT);
sendStickyBroadcast(broadcastIntent);
}}
IntentService经济舱:
public class MyService extends IntentService {
public static final String BG_PROCESS_INTENT = "com.mindspiker.Tester.MyService.TEST";
public static final String KEY_COUNTER = "counter";
public static final int MAX_COUNTER = 100;
public MyService() {
super("");
}
@Override
protected void onHandleIntent(Intent intent) {
for (int i = 0; i <= MAX_COUNTER; i++) {
Log.e("Service Example", " " + i);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
Intent broadcastIntent = new Intent();
broadcastIntent.setAction(BG_PROCESS_INTENT);
broadcastIntent.putExtra(KEY_COUNTER, i);
sendStickyBroadcast(broadcastIntent);
}
}}
清单文件条目:
应用前部分:
uses-permission android:name="com.mindspiker.Tester.MyService.TEST"
uses-permission android:name="android.permission.BROADCAST_STICKY"
应用程序内部部分
service android:name=".MyService"