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

这是我面对这个问题时的解决方案: ProgressDialog不是一个Fragment子,所以我的自定义类“ProgressDialogFragment”可以扩展DialogFragment,以保持对话框显示的配置更改。

import androidx.annotation.NonNull;
import android.app.Dialog;
import android.app.ProgressDialog;
import android.os.Bundle; 
import androidx.fragment.app.DialogFragment;
import androidx.fragment.app.FragmentManager;

 /**
 * Usage:
 * To display the dialog:
 *     >>> ProgressDialogFragment.showProgressDialogFragment(
 *              getSupportFragmentManager(), 
 *              "fragment_tag", 
 *              "my dialog title", 
 *              "my dialog message");
 *              
 * To hide the dialog
 *     >>> ProgressDialogFragment.hideProgressDialogFragment();
 */ 


public class ProgressDialogFragment extends DialogFragment {

    private static String sTitle, sMessage;
    private static ProgressDialogFragment sProgressDialogFragment;

    public ProgressDialogFragment() {
    }

    private ProgressDialogFragment(String title, String message) {
        sTitle = title;
        sMessage = message;
    }


    @NonNull
    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        return ProgressDialog.show(getActivity(), sTitle, sMessage);
    }

    public static void showProgressDialogFragment(FragmentManager fragmentManager, String fragmentTag, String title, String message) {
        if (sProgressDialogFragment == null) {
            sProgressDialogFragment = new ProgressDialogFragment(title, message);
            sProgressDialogFragment.show(fragmentManager, fragmentTag);

        } else { // case of config change (device rotation)
            sProgressDialogFragment = (ProgressDialogFragment) fragmentManager.findFragmentByTag(fragmentTag); // sProgressDialogFragment will try to survive its state on configuration as much as it can, but when calling .dismiss() it returns NPE, so we have to reset it on each config change
            sTitle = title;
            sMessage = message;
        }

    }

    public static void hideProgressDialogFragment() {
        if (sProgressDialogFragment != null) {
            sProgressDialogFragment.dismiss();
        }
    }
}

我们面临的挑战是在屏幕上保留对话框标题和消息 当它们重置为默认空字符串时旋转,尽管对话框仍然显示

有两种方法可以解决这个问题:

第一种方法: 使利用对话框的活动在manifest文件中的配置更改期间保留状态:

android:configChanges="orientation|screenSize|keyboardHidden"

谷歌不喜欢此方法。

第二种方法: 在活动的onCreate()方法上,如果savedInstanceState不为空,你需要通过重新构建ProgressDialogFragment来保留你的对话片段。

@Override
protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_deal);

 if (savedInstanceState != null) {
      ProgressDialogFragment saveProgressDialog = (ProgressDialogFragment) getSupportFragmentManager()
              .findFragmentByTag("fragment_tag");
      if (saveProgressDialog != null) {
          showProgressDialogFragment(getSupportFragmentManager(), "fragment_tag", "my dialog title", "my dialog message");
      }
  }
}

其他回答

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。

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.

最初的问题是代码无法在屏幕方向改变时存活下来。显然,这是“解决”的程序处理屏幕方向变化本身,而不是让UI框架做它(通过调用onDestroy)。

I would submit that if the underlying problem is that the program will not survive onDestroy(), then the accepted solution is just a workaround that leaves the program with serious other problems and vulnerabilities. Remember that the Android framework specifically states that your activity is at risk for being destroyed almost at any time due to circumstances outside your control. Therefore, your activity must be able to survive onDestroy() and subsequent onCreate() for any reason, not just a screen orientation change.

如果你要接受自己处理屏幕方向变化来解决OP的问题,你需要验证onDestroy()的其他原因不会导致相同的错误。你能做到吗?如果不是,我会质疑这个“公认的”答案是否真的是一个很好的答案。

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。

我发现了一个更容易的解决方案来处理线程时,方向改变。你可以只保留一个静态引用到你的活动/片段,并在对ui进行操作之前验证它是否为空。我建议使用try catch:

 public class DashListFragment extends Fragment {
     private static DashListFragment ACTIVE_INSTANCE;

     @Override
     public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ACTIVE_INSTANCE = this;

        new Handler().postDelayed(new Runnable() {
            public void run() {
                try {
                        if (ACTIVE_INSTANCE != null) {
                            setAdapter(); // this method do something on ui or use context
                        }
                }
                catch (Exception e) {}


            }
        }, 1500l);

    }

    @Override
    public void onDestroy() {
        super.onDestroy();

        ACTIVE_INSTANCE = null;
    }


}