Android-android为什么在application类里面发送runnable失败？

Question

在派生的Application类里面创建一个加载线程，当数据加载完毕的时候，加载线程往主线程发一个runnable,貌似发送失败了。代码如下：

class MyApp extends Application
{
   public void onCreate()
   {
         LoaderThread t = new LoaderThread();
         t.start();
   }

   private class LoaderThread extends Thread
   {
        public void run()
        {
             SystemClock.sleep(2000);
             boolean res = m_handler.post(m_runnable);
             if(res)
                Log.d(TAG, "Posted Runnable");
        }
   }

   private final Handler m_handler = new Handler();
   private final Runnable m_runnable = new Runnable() {
             public void run()
             {
                 Log.d(TAG, "Hey, i'm runnable!");
             }
        }
}

Answer 1

我们知道handler 一般理解成啥，一消息队列的机制处理好一个个的消息，然后给主线自己慢慢处理对吧。 你自己看下Handler 的构造方法，

public Handler(Looper looper) {
mLooper = looper;
mQueue = looper.mQueue;
mCallback = null;
}

/**
* Default constructor associates this handler with the queue for the
* current thread.
*
* If there isn't one, this handler won't be able to receive messages.
*/
public Handler() {
if (FIND_POTENTIAL_LEAKS) {
final Class<? extends Handler> klass = getClass();
if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) &&
(klass.getModifiers() & Modifier.STATIC) == 0) {
Log.w(TAG, "The following Handler class should be static or leaks might occur: " +
klass.getCanonicalName());
}
}

mLooper = Looper.myLooper();
if (mLooper == null) {
throw new RuntimeException(
"Can't create handler inside thread that has not called Looper.prepare()");
}
mQueue = mLooper.mQueue;
mCallback = null;
}

看到没有，handler 关键的是需要一个looper ，你在avtivity 中new Handler 默认使用的都是主线程的looper , 而你继承了Application ，之后，必须得在配置文件中。

 <application
android:name=".MyAppTest"
android:icon="@drawable/icon" android:label="@string/app_name" >
<activity android:name=".MainActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>

</application>

在<application>绑定使用，不然两者的Context 不一样，Looper 自然就有问题。
绑定使用必然没有问题，小包亲测//
03-12 14:33:16.154: DEBUG/test(2004): onCreate
03-12 14:33:18.163: DEBUG/test(2004): Hey, i'm runnable!
03-12 14:33:18.163: DEBUG/test(2004): Posted Runnable

Answer 2

可以运行啊
<application
android:name=".MyApp"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name" >

Answer 3

把LoaderThread做简单修改如下：

 private class LoaderThread extends Thread
{
@Override
public void run()
{
try {
while(true) {
sleep(2000);
m_handler.post(m_runnable);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
Log.d(TAG, "Posted Runnable");
}
}

或者把
m_handler.post(m_runnable);
改成 m_handler.postDelayed(m_runnable, 1000);
试试！