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

我也遇到了同样的问题,我想出了一个不使用ProgressDialog的解决方案,我得到了更快的结果。

我所做的是创建一个布局,其中有一个ProgressBar。

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<ProgressBar
    android:id="@+id/progressImage"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerInParent="true"
    />
</RelativeLayout>

然后在onCreate方法中执行以下操作

public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    setContentView(R.layout.progress);
}

然后在线程中执行长任务,完成后使用Runnable将内容视图设置为您想要用于此活动的实际布局。

例如:

mHandler.post(new Runnable(){

public void run() {
        setContentView(R.layout.my_layout);
    } 
});

这就是我所做的,我发现它比显示ProgressDialog运行得更快,在我看来,它的侵入性更小,外观更好。

然而,如果你想要使用ProgressDialog,那么这个答案不适合你。

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。

我什么都试过了。花了几天时间做实验。我不想阻止活动旋转。我的设想是:

向用户显示动态信息的进度对话框。例如:“连接到服务器…”,“下载数据…”,等等。 一个线程做繁重的工作,更新对话框 在最后用结果更新UI。

The problem was, when rotating the screen, every solution on the book failed. Even with the AsyncTask class, which is the correct Android way of dealing with this situations. When rotating the screen, the current Context that the starting thread is working with, is gone, and that messes up with the dialog that is showing. The problem was always the Dialog, no matter how many tricks I added to the code (passing new contexts to running threads, retaining thread states through rotations, etc...). The code complexity at the end was always huge and there was always something that could go wrong.

对我来说唯一有效的解决方案就是“活动/对话”技巧。这很简单,很天才,而且都是旋转证明:

Instead of creating a Dialog and ask to show it, create an Activity that has been set in the manifest with android:theme="@android:style/Theme.Dialog". So, it just looks like a dialog. Replace showDialog(DIALOG_ID) with startActivityForResult(yourActivityDialog, yourCode); Use onActivityResult in the calling Activity to get the results from the executing thread (even the errors) and update the UI. On your 'ActivityDialog', use threads or AsyncTask to execute long tasks and onRetainNonConfigurationInstance to save "dialog" state when rotating the screen.

这是快速和工作良好。我仍然使用对话框的其他任务和AsyncTask的一些东西,不需要一个固定的对话框在屏幕上。但在这种情况下,我总是使用活动/对话框模式。

而且,我没有尝试它,但它甚至可以阻止活动/对话框旋转,当线程运行时,加速事情,同时允许调用活动旋转。

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。

最简单和最灵活的解决方案是使用带有ProgressBar静态引用的AsyncTask。这为方向更改问题提供了一个封装的、因此可重用的解决方案。这个解决方案很好地帮助我完成了各种异步任务,包括互联网下载、与服务通信和文件系统扫描。该解决方案已经在多个安卓版本和手机型号上进行了良好的测试。完整的演示可以在DownloadFile.java中找到

下面是一个概念示例

public class SimpleAsync extends AsyncTask<String, Integer, String> {
    private static ProgressDialog mProgressDialog = null;
    private final Context mContext;

    public SimpleAsync(Context context) {
        mContext = context;
        if ( mProgressDialog != null ) {
            onPreExecute();
        }
    }

    @Override
    protected void onPreExecute() {
        mProgressDialog = new ProgressDialog( mContext );
        mProgressDialog.show();
    }

    @Override
    protected void onPostExecute(String result) {
        if ( mProgressDialog != null ) {
            mProgressDialog.dismiss();
            mProgressDialog = null;
        }
    }

    @Override
    protected void onProgressUpdate(Integer... progress) {
        mProgressDialog.setProgress( progress[0] );
    }

    @Override
    protected String doInBackground(String... sUrl) {
        // Do some work here
        publishProgress(1);
        return null;
    }

    public void dismiss() {
        if ( mProgressDialog != null ) {
            mProgressDialog.dismiss();
        }
    }
}

在Android Activity中的使用很简单

public class MainActivity extends Activity {
    DemoServiceClient mClient = null;
    DownloadFile mDownloadFile = null;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate( savedInstanceState );
        setContentView( R.layout.main );
        mDownloadFile = new DownloadFile( this );

        Button downloadButton = (Button) findViewById( R.id.download_file_button );
        downloadButton.setOnClickListener( new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                mDownloadFile.execute( "http://www.textfiles.com/food/bakebred.txt");
            }
        });
    }

    @Override
    public void onPause() {
        super.onPause();
        mDownloadFile.dismiss();
    }
}