浅谈setOnClickListener使用方法

setOnClickListener是Android开发中常用的点击事件监听器，多用于页面按钮调用。它的实现方法比较特殊，是通过回调实现的。下面看看它的源码

1. /**
2. * Register a callback to be invoked when this view is clicked. If this view is not
3. * clickable, it becomes clickable.
4. *
5. * @param l The callback that will run
6. *
7. * @see #setClickable(boolean)
8. */
9. public void setOnClickListener(@Nullable OnClickListener l) {
10. if (!isClickable()) {
11. setClickable(true);
12. }
13. getListenerInfo().mOnClickListener = l;
14. }

可以看到该控件是继承自View.java类， 在调用时传入一个setOnClickListener对象作为参数，该对象是一个接口类型的，其源码如下：

1. /**
2. * Interface definition for a callback to be invoked when a view is clicked.
3. */
4. public interface OnClickListener {
5. /**
6. * Called when a view has been clicked.
7. *
8. * @param v The view that was clicked.
9. */
10. void onClick(View v);
11. }

在OnClickListener接口中声明了一个onClick方法，需要我们在调用时实现。通过实践可以发现，当你传入了一个new View.OnClickListener()的参数时，Android Studio会自动补全onClick(View v)方法并让你去实现。在实现了onClick()方法后，它会在View的某个地方被调用，这就是回调的流程。下面是view中具体执行代码：

1. /**
2. * Call this view's OnClickListener, if it is defined. Performs all normal
3. * actions associated with clicking: reporting accessibility event, playing
4. * a sound, etc.
5. *
6. * @return True there was an assigned OnClickListener that was called, false
7. * otherwise is returned.
8. */
9. // NOTE: other methods on View should not call this method directly, but performClickInternal()
10. // instead, to guarantee that the autofill manager is notified when necessary (as subclasses
11. // could extend this method without calling super.performClick()).
12. public boolean performClick() {
13. // We still need to call this method to handle the cases where performClick() was called
14. // externally, instead of through performClickInternal()
15. notifyAutofillManagerOnClick();
16. final boolean result;
17. final ListenerInfo li = mListenerInfo;
18. if (li != null && li.mOnClickListener != null) {
19. playSoundEffect(SoundEffectConstants.CLICK);
20. li.mOnClickListener.onClick(this);
21. result = true;
22. } else {
23. result = false;
24. }
25. sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
26. notifyEnterOrExitForAutoFillIfNeeded(true);
27. return result;
28. }

该方法调用了onClick()