一 假设
override fun setContentView(contentView: View?) {
super.setContentView(contentView)
contentView?.viewTreeObserver?.addOnGlobalFocusChangeListener {
oldFocus, newFocus ->
doWork()
}
}
通过viewTreeObserver里进行全局焦点变化监听，但是会发现，pop dismiss一次后，以后弹出来上述的焦点回调方法都不会调用了。
二 验证
猜想是不是dismiss方法做了什么处理，于是查看源码：
public void dismiss() {
//***
final View contentView = mContentView;
//***
dismissImmediate(decorView, contentHolder, contentView);
//**
}
/**
* Removes the popup from the window manager and tears down the supporting
* view hierarchy, if necessary.
*/
private void dismissImmediate(View decorView, ViewGroup contentHolder, View contentView) {
// If this method gets called and the decor view doesn't have a parent,
// then it was either never added or was already removed. That should
// never happen, but it's worth checking to avoid potential crashes.
if (decorView.getParent() != null) {
mWindowManager.removeViewImmediate(decorView);
}
if (contentHolder != null) {
contentHolder.removeView(contentView);
}
// This needs to stay until after all transitions have ended since we
// need the reference to cancel transitions in preparePopup().
mDecorView = null;
mBackgroundView = null;
mIsTransitioningToDismiss = false;
}
可以发现，contentView的引用在dismiss时断掉的。
所以显然要想实现pop的焦点持续（不断弹出/取消）监听，contentView?.viewTreeObserver?.addOnGlobalFocusChangeListener 就要具有即时性。那么show方法是不是会满足每次调用的时候都会创建contentView新的执行对象呢？
showAtLocation->preparePop->createBackgroundView(mContentView)->backgroundView.addView(contentView,*)->
// We may wrap that in another view, so we'll need to manually specify
// the surface insets.
WindowManager.LayoutParams对象.setSurfaceInsets(mBackgroundView, true /*manual*/, true /*preservePrevious*/);
可以看到，contentView是在show的时候第一次或者再次被添加到pop中去的。
但是即便contentView被断掉了和pop的DecorView的联系，其再次联系上时，之前的监听怎么就无法生效了呢，此时应该同样能接收焦点事件的啊？
我们来做这样一个监听：
override fun setContentView(contentView: View?) {
super.setContentView(contentView)
log("setContentView viewTreeObserver=${
contentView?.viewTreeObserver}")
}
override fun showAtLocation(parent: View?, gravity: Int, x: Int, y: Int) {
log("showBefore viewTreeObserver=${
contentView?.viewTreeObserver}")
super.showAtLocation(parent, gravity, x, y)
log("showAfter viewTreeObserver=${
contentView?.viewTreeObserver}")
contentView?.viewTreeObserver?.addOnGlobalFocusChangeListener {
oldFocus, newFocus ->
doWork()
}
}
日志输出结果：
第一次创建并show
setContentView viewTreeObserver=android.view.ViewTreeObserver@b5a93e2
showBefore viewTreeObserver=android.view.ViewTreeObserver@b5a93e2
showAfter viewTreeObserver=android.view.ViewTreeObserver@b5a93e2
dismiss掉后第二次show
showBefore viewTreeObserver=android.view.ViewTreeObserver@3d4f5af
showAfter viewTreeObserver=android.view.ViewTreeObserver@3d4f5af
可以看到showBefore的时候id已经发生了变化，所以说明在show之前已经变化了。因此这就是监听不到的原因。
三 方案
因此，最终实现的方案就是：在show的时候再次addOnGlobalFocusChangeListener
override fun showAtLocation(parent: View?, gravity: Int, x: Int, y: Int) {
super.showAtLocation(parent, gravity, x, y)
contentView?.viewTreeObserver?.addOnGlobalFocusChangeListener {
oldFocus, newFocus ->
doWork()
}
}
有没有更优雅的方式，毕竟还有showAsDropdown，难不成要一一去写？
貌似还只能这么做。
另外pop中 EditText变化则没有纳入以上监听，所以还需要另外处理。
