java 恢复活动时“线程已启动”
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"Thread already started" when resuming the activity
提问by NioX5199
Here is my situation: I am building a game for android and my game's activity is composed of a custom surfaceView which has a thread for the game logic and rendering. The architecture is similar to the LunarLander demo from Google's website.
这是我的情况：我正在为 android 构建一个游戏，我的游戏活动由一个自定义的 SurfaceView 组成，它有一个用于游戏逻辑和渲染的线程。该架构类似于 Google 网站上的 LunarLander 演示。
When the activity starts it creates the surfaceView and calls this method:
当活动开始时，它会创建surfaceView并调用这个方法：
@Override
public void surfaceCreated(SurfaceHolder holder)
{
renderThread.start();
}
When I press the home button to exit the game, the onPause() method is called, which calls surfaceDestroyed(). In surfaceDestroyed I stop the game Thread by calling:
当我按下home键退出游戏时，onPause()方法被调用，该方法调用surfaceDestroyed()。在surfaceDestroyed中，我通过调用来停止游戏线程：
@Override
public void surfaceDestroyed(SurfaceHolder holder)
{
synchronized(holder)
{
renderThread.stop();
}
}
The app goes to background fine. Then, when I relaunch the app by pressing the icon, I get a "Thread already started" message in the log along with a "force close" popup on the screen. This message happens when the activity enters the "surfaceCreated" method when it calls start() on the render thread.
该应用程序进入后台正常。然后，当我通过按下图标重新启动应用程序时，我会在日志中收到一条“线程已启动”消息，并在屏幕上显示“强制关闭”弹出窗口。当活动在渲染线程上调用 start() 时进入“surfaceCreated”方法时，会发生此消息。
Now I've looked into it for hours and can't figure out why this is. I believe my thread is stopped when I close the app so I don't understand why it says it has already started.
现在我已经研究了几个小时，但不知道为什么会这样。我相信当我关闭应用程序时我的线程已停止，所以我不明白为什么它说它已经开始。
采纳答案by Michael Borgwardt
Those methods don't do what you think they do. From the API doc:
这些方法不会做您认为它们会做的事情。来自API 文档：
It is never legal to start a thread more than once.
多次启动一个线程是不合法的。
And:
和：
public final void stop()- Deprecated. This method is inherently unsafe.
public final void stop()- 已弃用。这种方法本质上是不安全的。
If you want to pause a thread, you have to use Object.wait()and Objecft.notifyAll()from within the thread.
如果要暂停线程，则必须在线程内使用Object.wait()和Objecft.notifyAll()。
回答by Torben
In my opinion you should not pack your code into a subclass of Thread if you intend to be starting and stopping the Thread often (the examples do it because it makes the code shorter). Use a Runnable instead. That way you can stop and discard the old Thread when you want and create a new Thread object to execute the Runnable when you need to start it again.
在我看来，如果您打算经常启动和停止 Thread，则不应将代码打包到 Thread 的子类中（示例这样做是因为它使代码更短）。请改用 Runnable。这样，您可以在需要时停止并丢弃旧的 Thread，并在需要再次启动它时创建一个新的 Thread 对象来执行 Runnable。
private TutorialRunnable tutorialRunnable;
...
// Synchronization and error checking omitted for brevity.
public void surfaceCreated(SurfaceHolder holder) {
thread = new Thread(tutorialRunnable);
thread.start();
}
public void surfaceDestroyed(SurfaceHolder holder) {
tutorialRunnable.setRunning(false);
while (thread != null) {
try {
thread.join();
thread = null;
} catch (InterruptedException e) {
}
}
}
Also, relying on exceptions is bad form. That should be used as a last resort when your own code behaves unexpectedly.
此外，依赖异常是不好的形式。当您自己的代码出现意外行为时，这应该用作最后的手段。
回答by AZ_
A bad solution but it works..
一个糟糕的解决方案，但它有效..
public void surfaceCreated(SurfaceHolder holder) {
try{
_thread.setRunning(true);
_thread.start();
}catch(Exception ex){
_thread = new TutorialThread(getHolder(), this);
_thread.start();
}
}
corrections are warmly welcomed.
热烈欢迎更正。
