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。


当前回答

这是我提出的解决方案:

Move the AsyncTask or Thread to a retained Fragment, as explained here. I believe it is a good practice to move all network calls to fragments. If you are already using fragments, one of them could be made responsible for the calls. Otherwise, you can create a fragment just for doing the request, as the linked article proposes. The fragment will use a listener interface to signal the task completion/failure. You don't have to worry for orientation changes there. The fragment will always have the correct link to the current activity and progress dialog can be safely resumed. Make your progress dialog a member of your class. In fact you should do that for all dialogs. In the onPause method you should dismiss them, otherwise you will leak a window on the configuration change. The busy state should be kept by the fragment. When the fragment is attached to the activity, you can bring up the progress dialog again, if the call is still running. A void showProgressDialog() method can be added to the fragment-activity listener interface for this purpose.

其他回答

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。

如果你创建了一个后台服务来完成所有繁重的工作(tcp请求/响应,解组),视图和活动可以被销毁并重新创建,而不会泄漏窗口或丢失数据。这允许Android推荐的行为,即在每次配置更改时销毁一个Activity。对于每个方向变化)。

它有点复杂,但它是调用服务器请求、数据预处理/后处理等的最佳方式。

您甚至可以使用您的服务将每个请求排队到服务器,因此它使处理这些事情变得简单和高效。

开发指南有一个关于服务的完整章节。

看起来太“快速和肮脏”了,所以请指出缺点,但我发现有用的是……

在我的AsyncTask的onPostExecute方法中,我简单地包装了`。try/catch块中的进度对话框(带有空捕获)的Dismiss ',然后简单地忽略所引发的异常。似乎是错误的,但似乎没有不良影响(至少对于我随后所做的事情,这是启动另一个活动,将我的长时间运行查询的结果传递为一个额外)

我也遇到过同样的问题。我的活动需要从一个URL解析一些数据,它很慢。所以我创建了一个线程来完成这个任务,然后显示一个进度对话框。当线程完成时,我让线程通过处理程序发布消息回UI线程。在处理程序。handleMessage,我从线程获得数据对象(现在准备好了),并将其填充到UI。这和你的例子很相似。

经过反复试验,我似乎找到了解决办法。至少现在我可以在任何时候旋转屏幕,在线程完成之前或之后。在所有测试中,对话框都是正确关闭的,所有行为都符合预期。

我所做的如下所示。目标是填充我的数据模型(mDataObject),然后将其填充到UI。应该允许屏幕旋转在任何时候没有意外。

class MyActivity {

    private MyDataObject mDataObject = null;
    private static MyThread mParserThread = null; // static, or make it singleton

    OnCreate() {
        ...
        Object retained = this.getLastNonConfigurationInstance();
        if(retained != null) {
            // data is already completely obtained before config change
            // by my previous self.
            // no need to create thread or show dialog at all
            mDataObject = (MyDataObject) retained;
            populateUI();
        } else if(mParserThread != null && mParserThread.isAlive()){
            // note: mParserThread is a static member or singleton object.
            // config changed during parsing in previous instance. swap handler
            // then wait for it to finish.
            mParserThread.setHandler(new MyHandler());
        } else {
            // no data and no thread. likely initial run
            // create thread, show dialog
            mParserThread = new MyThread(..., new MyHandler());
            mParserThread.start();
            showDialog(DIALOG_PROGRESS);
        }
    }

    // http://android-developers.blogspot.com/2009/02/faster-screen-orientation-change.html
    public Object onRetainNonConfigurationInstance() {
        // my future self can get this without re-downloading
        // if it's already ready.
        return mDataObject;
    }

    // use Activity.showDialog instead of ProgressDialog.show
    // so the dialog can be automatically managed across config change
    @Override
    protected Dialog onCreateDialog(int id) {
        // show progress dialog here
    }

    // inner class of MyActivity
    private class MyHandler extends Handler {
        public void handleMessage(msg) {
            mDataObject = mParserThread.getDataObject();
            populateUI();
            dismissDialog(DIALOG_PROGRESS);
        }
    }
}

class MyThread extends Thread {
    Handler mHandler;
    MyDataObject mDataObject;

    // constructor with handler param
    public MyHandler(..., Handler h) {
        ...
        mHandler = h;
    }

    public void setHandler(Handler h) { mHandler = h; } // for handler swapping after config change
    public MyDataObject getDataObject() { return mDataObject; } // return data object (completed) to caller

    public void run() {
        mDataObject = new MyDataObject();
        // do the lengthy task to fill mDataObject with data
        lengthyTask(mDataObject);
        // done. notify activity
        mHandler.sendEmptyMessage(0); // tell activity: i'm ready. come pick up the data.
    }
}

这对我来说很有效。我不知道这是否是Android设计的“正确”方法——他们声称这种“在屏幕旋转期间破坏/重建活动”实际上使事情变得更简单,所以我猜这应该不是太棘手。

如果您在我的代码中发现问题,请告诉我。如上所述,我真的不知道是否有任何副作用。

对于这些问题,我想出了一个坚如磐石的解决方案,它符合“Android方式”。我使用IntentService模式进行所有长时间运行的操作。

也就是说,我的活动广播意图,IntentService负责工作,将数据保存在DB中,然后广播粘性意图。粘性部分很重要,即使Activity在用户启动工作后暂停,并且错过了来自IntentService的实时广播,我们仍然可以响应并从调用Activity中获取数据。progressdialog可以很好地使用onSaveInstanceState()与此模式一起工作。

Basically, you need to save a flag that you have a progress dialog running in the saved instance bundle. Do not save the progress dialog object because this will leak the entire Activity. To have a persistent handle to the progress dialog, I store it as a weak reference in the application object. On orientation change or anything else that causes the Activity to pause (phone call, user hits home etc.) and then resume, I dismiss the old dialog and recreate a new dialog in the newly created Activity.

对于无限进度对话框来说,这很容易。对于进度条样式,您必须将最后一个已知的进度放在bundle中,并将您在活动中本地使用的任何信息用于跟踪进度。在恢复进度时,您将使用此信息以与之前相同的状态重新生成进度条,然后根据当前状态进行更新。

总之,将长时间运行的任务放到IntentService中,再加上明智地使用onSaveInstanceState(),可以让你有效地跟踪对话框,并在活动生命周期事件中恢复对话框。活动代码的相关部分如下。您还需要BroadcastReceiver中的逻辑来适当地处理Sticky意图,但这超出了本文的范围。

public void doSignIn(View view) {
    waiting=true;
    AppClass app=(AppClass) getApplication();
    String logingon=getString(R.string.signon);
    app.Dialog=new WeakReference<ProgressDialog>(ProgressDialog.show(AddAccount.this, "", logingon, true));
    ...
}

@Override
protected void onSaveInstanceState(Bundle saveState) {
    super.onSaveInstanceState(saveState);
    saveState.putBoolean("waiting",waiting);
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if(savedInstanceState!=null) {
        restoreProgress(savedInstanceState);    
    }
    ...
}

private void restoreProgress(Bundle savedInstanceState) {
    waiting=savedInstanceState.getBoolean("waiting");
    if (waiting) {
        AppClass app=(AppClass) getApplication();
        ProgressDialog refresher=(ProgressDialog) app.Dialog.get();
        refresher.dismiss();
        String logingon=getString(R.string.signon);
        app.Dialog=new WeakReference<ProgressDialog>(ProgressDialog.show(AddAccount.this, "", logingon, true));
    }
}