ContentObserver onChange

Question

ContentObserver的文档对我来说并不清楚。在哪个线程上调用ContentObserver的onChange？

我检查过了，它不是你创建观察者的线程。它看起来像是发送通知的线程，但我没有找到有关它的文档。

Answer 1

执行ContentObserver.onChange()方法的Thread是ContentObserver构造函数(http://developer.android.com/reference/android/database/ContentObserver.html#ContentObserver(android.os.Handler%29)'sHandler的Looper(https://developer.android.com/reference/android/os/Handler.html#getLooper(%29)'s Thead.

例如，要让它在主UI线程上运行，代码可能如下所示：

// returns the applications main looper (which runs on the application's 
// main UI thread)
Looper looper = Looper.getMainLooper();

// creates the handler using the passed looper
Handler handler = new Handler(looper);

// creates the content observer which handles onChange on the UI thread
ContentObserver observer = new MyContentObserver(handler);

或者，要让它在新的工作线程上运行，代码可能如下所示：

// creates and starts a new thread set up as a looper
HandlerThread thread = new HandlerThread("MyHandlerThread");
thread.start();

// creates the handler using the passed looper
Handler handler = new Handler(thread.getLooper());

// creates the content observer which handles onChange on a worker thread
ContentObserver observer = new MyContentObserver(handler);

或者甚至让它在当前线程上运行，代码可能如下所示。通常，这不是您想要的，因为循环的Thread不能做更多的事情，因为Looper.loop()是阻塞调用。尽管如此：

// prepares the looper of the current thread
Looper.prepare();

// creates a handler for the current thread's looper.
Handler handler = new Handler();

// creates the content observer which handles onChange on this thread
ContentObserver observer = new MyContentObserver(handler);

// starts the current thread's looper (blocking call because it's 
// looping, and handling messages forever). the content observer will
// only execute the onChange method while the thread is looping; 
// interrupting Looper.loop() would "break" the content observer.
Looper.loop();

Answer 2

为了确保在UI线程上调用onChange，请在注册时使用正确的处理程序：

Handler handler = new Handler(Looper.getMainLooper());
ContentObserver observer = new MyContentObserver(handler);
...

Answer 3

这个老问题似乎触及了你的问题：

How to observe contentprovider change? android

看起来您应该创建一个新线程，在它自己的服务中运行，其中将调用onChange方法。