如何合理使用安卓Handler

最新推荐文章于 2025-03-31 17:54:40 发布

转载最新推荐文章于 2025-03-31 17:54:40 发布 · 510 阅读

文章标签：

#handler #安卓 #handler使用 #handler销毁 #销毁handler

Android 专栏收录该内容

221 篇文章

订阅专栏

本文介绍了如何在Android应用中正确使用Handler以避免内存泄漏的问题。通过将Handler定义为静态内部类，并持有对其所在Activity的弱引用，可以有效防止内存泄漏的发生。此外，还提供了在Activity生命周期的不同阶段管理Handler的方法。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

我们在刚接触Handler的时候，包括很多视频教程的老师，为了省事，都是这样使用Handler的：

private Handler mHandler = new Handler() {

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
            case 1:
                mImageView.setImageBitmap(bitmap);
                break;
            case 2:
                Toast.makeText(getApplicationContext(), "连接服务器失败...", Toast.LENGTH_SHORT).show();
                break;

            default:
                break;
            }
            super.handleMessage(msg);
        }
    };

稍微细心的同学会发现，这样写的话eclipse会提示“This Handler class should be static or leaks might occur ”，也就是说这样写可能会导致内存泄漏。查了一下资料，网友是这样解决的：

private MyHandler mHandler = new MyHandler(this);
/**
 * 定义一个静态内部类，继承Handler，让它持有本Activity的弱引用
 *
 */
private static class MyHandler extends Handler {
    // CameraVideoActivity是当前的Activity
    WeakReference<CameraVideoActivity> mActivityReference;

    MyHandler(CameraVideoActivity activity) {
        mActivityReference = new WeakReference<CameraVideoActivity>(activity);
    }

    @Override
    public void handleMessage(Message msg) {
        final CameraVideoActivity activity = mActivityReference.get();
        if (activity != null) {
            switch (msg.what) {
            case 1:
                activity.mImageView.setImageBitmap(activity.bitmap);
                break;
            case 2:
                Toast.makeText(activity, "连接服务器失败...", Toast.LENGTH_SHORT).show();
                break;

            default:
                break;
            }
            super.handleMessage(msg);
        }
    }
}

在onDestroy()方法移除Handler中的message

@Override
protected void onDestroy() {
    // TODO Auto-generated method stub
    super.onDestroy();
    if (null != mHandler) {
        // 在程序中应该写为常量，这里为了让大家看明白，直接把常量的值写出来
        mHandler.removeMessages(1);
        mHandler.removeMessages(2);
    }
}

以上内存泄漏问题解决了，美中不足的是每次使用view之前都要做空指针判断。另一个使用例子：

/*
It sounds like the activity finishes its lifecycle before the Handler executes the code. You can manage a handler.post(runnable) by creating an instance member for the handler and runnable, then managing the handler in the Activity Lifecycle methods.
*/
private Handler myHandler;
private Runnable myRunnable = new Runnable() {
    @Override
    public void run() {
        //Do Something
    }
};
// Start the runnable with handler.post.
protected void onStart() {
    super.onStart();
    myHandler = new Handler();
    myHandler.post(myRunnable);

}
//If the runnable hasn't executed by the time onStop is called, we don't want to run it. Remove the callback in the onStop method:

protected void onStop() {
    super.onStop();
    mHandler.removeCallbacks(myRunnable);
}

http://www.google.ie/url?q=http://stackoverflow.com/questions/5819140/how-to-stop-handler-in-android&sa=U&ei=f9xbVaiXNISqggS8-YGwBg&ved=0CBoQFjAB&usg=AFQjCNER1hvSx2CG4QG9bYygTQySfxaMIg