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。
我有一个实现,允许活动在屏幕方向改变上被销毁,但仍然在重新创建的活动中成功地销毁对话框。
我用…NonConfigurationInstance将后台任务附加到重新创建的活动。
正常的Android框架处理重新创建对话框本身,没有任何改变。
我子类化了AsyncTask,为“拥有”活动添加了一个字段,以及一个更新这个所有者的方法。
class MyBackgroundTask extends AsyncTask<...> {
MyBackgroundTask (Activity a, ...) {
super();
this.ownerActivity = a;
}
public void attach(Activity a) {
ownerActivity = a;
}
protected void onPostExecute(Integer result) {
super.onPostExecute(result);
ownerActivity.dismissDialog(DIALOG_PROGRESS);
}
...
}
在我的活动类中,我添加了一个字段backgroundTask引用'owned' backgroundTask,我使用onRetainNonConfigurationInstance和getLastNonConfigurationInstance更新这个字段。
class MyActivity extends Activity {
public void onCreate(Bundle savedInstanceState) {
...
if (getLastNonConfigurationInstance() != null) {
backgroundTask = (MyBackgroundTask) getLastNonConfigurationInstance();
backgroundTask.attach(this);
}
}
void startBackgroundTask() {
backgroundTask = new MyBackgroundTask(this, ...);
showDialog(DIALOG_PROGRESS);
backgroundTask.execute(...);
}
public Object onRetainNonConfigurationInstance() {
if (backgroundTask != null && backgroundTask.getStatus() != Status.FINISHED)
return backgroundTask;
return null;
}
...
}
进一步改进建议:
在任务完成后,清除活动中的backgroundTask引用以释放与之关联的所有内存或其他资源。
在活动被销毁之前,清除后台任务中的ownerActivity引用,以防它不会立即被重新创建。
创建一个BackgroundTask接口和/或集合,以允许不同类型的任务从相同的活动中运行。
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。
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));
}
}
我是这样做的:
package com.palewar;
import android.app.Activity;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
public class ThreadActivity extends Activity {
static ProgressDialog dialog;
private Thread downloadThread;
final static Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
dialog.dismiss();
}
};
protected void onDestroy() {
super.onDestroy();
if (dialog != null && dialog.isShowing()) {
dialog.dismiss();
dialog = null;
}
}
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
downloadThread = (Thread) getLastNonConfigurationInstance();
if (downloadThread != null && downloadThread.isAlive()) {
dialog = ProgressDialog.show(ThreadActivity.this, "",
"Signing in...", false);
}
dialog = ProgressDialog.show(ThreadActivity.this, "",
"Signing in ...", false);
downloadThread = new MyThread();
downloadThread.start();
// processThread();
}
// Save the thread
@Override
public Object onRetainNonConfigurationInstance() {
return downloadThread;
}
static public class MyThread extends Thread {
@Override
public void run() {
try {
// Simulate a slow network
try {
new Thread().sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
handler.sendEmptyMessage(0);
} finally {
}
}
}
}
你也可以试着让我知道它对你是否有效