android - 获得 Looper 的最佳做法是什么？

Question

我已经尝试了 mContext.getMainLooper() 和 Looper.getMainLooper()。两者都返回相同的结果，但我想知道哪种方法正确？

我还从 Android 开发人员链接中阅读了这篇文章 this和 this :

For Looper.getMainLooper():

Looper getMainLooper () Returns the application's main looper, which lives in the main thread of the application.

For mContext.getMainLooper():

Looper getMainLooper () Return the Looper for the main thread of the current process. This is the thread used to dispatch calls to application components (activities, services, etc). By definition, this method returns the same result as would be obtained by calling Looper.getMainLooper().

Answer 1

getMainLooper() 作为一个方法，它会根据你调用它的方式返回相同的结果，所以你可以认为两者是一样的，因为从上下文中返回 Looper 会得到你从应用程序返回循环程序时得到相同的结果，为了更好地了解 Looper类并查看它如何返回循环器:

private static Looper sMainLooper;

public static Looper getMainLooper() {

    synchronized (Looper.class) {

        return sMainLooper;

    }

}

public static void prepareMainLooper() {

    prepare(false);

    synchronized (Looper.class) {

        if (sMainLooper != null) {

            throw new IllegalStateException(
                    "The main Looper has already been prepared.");

        }

        sMainLooper = myLooper();

    }

}

public static Looper myLooper() {

    return sThreadLocal.get();

}

并且在查看 ThreadLocal.class 中的 get() 方法时:

public T get() {

    Thread t = Thread.currentThread();

    ThreadLocalMap map = getMap(t);

    if (map != null) {

        ThreadLocalMap.Entry e = map.getEntry(this);

        if (e != null)

            return (T) e.value;

    }

    return setInitialValue();

}

和Thread.currentThread(); 根据Thread.class文档:

Returns: the currently executing thread.

在运行 android 的情况下，哪个线程持有上下文。

---

毕竟，我发现应该困扰您的不是如何获得主循环器，而是处理循环器时应该遵循的最佳实践是什么，例如何时使用 getMainLooper() 以及何时使用 Looper.prepare()，as described here :

Looper.prepareMainLooper() prepares looper in main UI thread. Android applications normally do not call this function. As main thread has its looper prepared long before first activity, service, provider or broadcast receiver is started.

But Looper.prepare() prepares Looper in current thread. After this function is called, thread can call Looper.loop() to start processing messages with Handlers.

你还应该知道getMainLooper() 和myLooper() 之间的区别，as described here :

getMainLooper

Returns the application's main looper, which lives in the main thread of the application.

myLooper

Return the Looper object associated with the current thread. Returns null if the calling thread is not associated with a Looper.