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。
诀窍是在onPreExecute/onPostExecute期间像往常一样在AsyncTask中显示/解散对话框,尽管在方向改变的情况下,在活动中创建/显示一个对话框的新实例,并将其引用传递给任务。
public class MainActivity extends Activity {
private Button mButton;
private MyTask mTask = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
MyTask task = (MyTask) getLastNonConfigurationInstance();
if(task != null){
mTask = task;
mTask.mContext = this;
mTask.mDialog = ProgressDialog.show(this, "", "", true);
}
mButton = (Button) findViewById(R.id.button1);
mButton.setOnClickListener(new View.OnClickListener(){
public void onClick(View v){
mTask = new MyTask(MainActivity.this);
mTask.execute();
}
});
}
@Override
public Object onRetainNonConfigurationInstance() {
String str = "null";
if(mTask != null){
str = mTask.toString();
mTask.mDialog.dismiss();
}
Toast.makeText(this, str, Toast.LENGTH_SHORT).show();
return mTask;
}
private class MyTask extends AsyncTask<Void, Void, Void>{
private ProgressDialog mDialog;
private MainActivity mContext;
public MyTask(MainActivity context){
super();
mContext = context;
}
protected void onPreExecute() {
mDialog = ProgressDialog.show(MainActivity.this, "", "", true);
}
protected void onPostExecute(Void result) {
mContext.mTask = null;
mDialog.dismiss();
}
@Override
protected Void doInBackground(Void... params) {
SystemClock.sleep(5000);
return null;
}
}
}
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