Question

我在Android应用的Looper内使用Service。通常它没有任何问题。但在某些情况下（例如，当我尝试调试我的应用程序时），它会显示应用程序内部存在竞争。 Looper即将开始，Thread和Handler正在startMessageThread()方法末尾调用的方法Service.onCreate()中创建。

比赛是因为还有其他方法和类使用在Looper.loop();之前初始化的类。在某些情况下，这些方法在Looper结束之前运行。它会产生NullPointerException。

public class MyService extends Service {

    private Thread thread;
    private Handler handler;

    @Override
    public void onCreate() {
        super.onCreate();
        //some code
        startMessageThread();
    }

    private void startMessageThread() {
        thread = new Thread() {

            @Override
            public void run() { 
                Looper.prepare();
                handler = new Handler() {

                    @Override
                    public void handleMessage(Message msg) {
                        switch (msg.what) {
                            //message handling
                        }
                    }
                };
                MyObject myObject = new MyObject(arg1, arg2);
                myObject.init();
                myObject.attr = myAttr;
                Looper.loop();
            }
        }              
    }
}

如果我是对的，这个问题非常相似How to create a Looper thread, then send it a message immediately?但我不想在创建'HandlerThread'之后立即发送任何消息。只是强制主线程在onCreate方法的Looper方法结束时等待。

我尝试在Service.onCreate方法的末尾添加了这个：

synchronized (thread) {
    try {
        if (looperRun) {
            wait();
        }
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

looperRun当然是boolean。我在looperRun = true;方法调用之前添加了Looper.loor();。这段代码在startMessageThread()方法的末尾。

if (looperRun) {            
    notify();
    looperRun = false;
}

在某些情况下，我有这个例外：

java.lang.RuntimeException: Unable to create service com.myapplication.service.MyService:
java.lang.IllegalMonitorStateException: object not locked by thread before wait()
    at android.app.ActivityThread.handleCreateService(ActivityThread.java:2582)
    at android.app.ActivityThread.access$1800(ActivityThread.java:135)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:136)
    at android.app.ActivityThread.main(ActivityThread.java:5017)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:515)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
    at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.IllegalMonitorStateException: object not locked by thread before wait()
    at java.lang.Object.wait(Native Method)
    at java.lang.Object.wait(Object.java:364)
    at com.myapplication.service.MyService.onCreate(MyService.java:162)
    at android.app.ActivityThread.handleCreateService(ActivityThread.java:2572)
    at android.app.ActivityThread.access$1800(ActivityThread.java:135)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:136)
    at android.app.ActivityThread.main(ActivityThread.java:5017)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:515)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
    at dalvik.system.NativeStart.main(Native Method)

修改

protected void startMessageThread() {
    MessageThread messageThread = new MessageThread("messageThread");
    messageThread.start();
    messageHandler = new Handler(messageThread.getLooper()) {

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                //message handling
            }
        }
    };
}

private class MessageThread extends HandlerThread {

    public MessageThread(String name) {
        super(name);
    }

    @Override
    public void run() {
        Looper.prepare();
        MyObject myObject = new MyObject(arg1, arg2);
        myObject.init();
        myObject.attr = myAttr;
        Looper.loop();
    }
}

编辑2

我尝试过与此类似的解决方案：How to create a Looper thread, then send it a message immediately?我的代码如下。但是我的应用程序似乎在启动后被冻结。

private class BackgroundThread extends HandlerThread {

    private Handler handler;

    public BackgroundThread(String name) {
        super(name);
    }

    @Override
    public void run() {
        Looper.prepare();
        backgroundHandler = new Handler() {

            @Override
            public void handleMessage(Message msg) {
                log.finest("DEAService message:" + msg.what);
                switch (msg.what) {
                    case MSG_INIT:                            
                        MyObject myObject = new MyObject(arg1, arg2);
                        myObject.init();
                        myObject.attr = myAttr;
                        break;
                    //message handling
                }
            }
        };
        Looper.loop();
    };

    public synchronized void waitUntilReady() {
        handler = new Handler(getMainLooper());
    }
}

我像以前一样在此方法中启动此HandlerThread：

protected void startBackgroundThread() {
    BackgroundThread backgroundThread = new BackgroundThread("backgroundThread");
    backgroundThread.start();
    backgroundThread.waitUntilReady();
    backgroundHandler.sendEmptyMessage(MSG_INIT);
}

正如我上面提到的 - 应用似乎在开始后被冻结。没有任何事情发生。

Answer 1

你永远不应该阻止主线程。从未！

我已经多次使用了这个非常方便的HandlerThread类：

HandlerThread ht = new HandlerThread("myThread");
ht.start();
Handler handler = new Handler(ht.getLooper());
handler.post(... stuff

也许你应该试一试

修改对不起，有两种方法可以处理，我的原始帖子是另一种。你正在使用的方式就是这样。

HandlerThread ht = new HandlerThread("myThread"); ht.start(); Handler handler = new Handler(ht.getLooper()){ @Override public void handleMessage(Message msg) { switch (msg.what) { //message handling } } };

新修改：

查看代码。

protected void startMessageThread() { HandlerThread messageThread = new HandlerThread("messageThread"); messageThread.start(); messageHandler = new Handler(messageThread.getLooper()) { @Override public void handleMessage(Message msg) { switch (msg.what) { case INIT: MyObject myObject = new MyObject(arg1, arg2); myObject.init(); myObject.attr = myAttr; break; } } }; messageHandler.sendEmptyMessage(INIT); }

Answer 2

我尝试过这段代码，一切似乎都运转良好。

private class BackgroundThread extends HandlerThread {

    private Handler handler;

    public BackgroundThread(String name) {
        super(name);
    }

    @Override
    public void run() {
        Looper.prepare();
        backgroundHandler = new Handler() {

            @Override
            public void handleMessage(Message msg) {
                log.finest("DEAService message:" + msg.what);
                switch (msg.what) {
                    //message handling
                }
            }
        };
        MyObject myObject = new MyObject(arg1, arg2);
        myObject.init();
        myObject.attr = myAttr;
        Looper.loop();
    };

    public synchronized void waitUntilReady() {
        handler = new Handler(getMainLooper());
    }
}

使用以下代码启动此HandlerThread：

protected void startBackgroundThread() {
    BackgroundThread backgroundThread = new BackgroundThread("backgroundThread");
    backgroundThread.start();
    backgroundThread.waitUntilReady();
}

如何强制主线程等待Looper结束其工作

2 个答案: