用实验方法学习View的事件传递机制

我写了一个UI界面，最外层是OuterLinearLayout，内层是InnerLayout，最里层是TargetButton，下面是实验输出的日志：

2018-11-25 22:15:27.288 28703-28703/work.cloud.com.myappcloudwork D/ttt: dispatchTouchEvent in OuterLinearLayout
2018-11-25 22:15:27.289 28703-28703/work.cloud.com.myappcloudwork D/ttt: onInterceptTouchEvent in OuterLinearLayout
2018-11-25 22:15:27.290 28703-28703/work.cloud.com.myappcloudwork D/ttt: dispatchTouchEvent in InnerLayout
2018-11-25 22:15:27.290 28703-28703/work.cloud.com.myappcloudwork D/ttt: onInterceptTouchEvent in InnerLayout
2018-11-25 22:15:27.291 28703-28703/work.cloud.com.myappcloudwork D/ttt: dispatchTouchEvent in TargetButton
2018-11-25 22:15:27.292 28703-28703/work.cloud.com.myappcloudwork D/ttt: onTouchEvent in TargetButton
2018-11-25 22:15:27.294 28703-28703/work.cloud.com.myappcloudwork D/ttt: onTouchEvent in InnerLayout
2018-11-25 22:15:27.295 28703-28703/work.cloud.com.myappcloudwork D/ttt: onTouchEvent in OuterLinearLayout

从日志可以看出，touch事件经过每一层View时，先执行dispatchTouchEvent方法，然后执行onInterceptTouchEvent，以此情形直至布局的最里层，我这里是一个普通View，叫TargetButton；然后可以看出从内向外以此执行onTouchEvent方法。

如果某层做了拦截，即该层ViewGroup的onInterceptTouchEvent返回值设为true，那么touch事件不再向下传递，实验输入日志为：

2018-11-25 22:30:03.303 29787-29787/work.cloud.com.myappcloudwork D/ttt: dispatchTouchEvent in OuterLinearLayout
2018-11-25 22:30:03.304 29787-29787/work.cloud.com.myappcloudwork D/ttt: onInterceptTouchEvent in OuterLinearLayout
2018-11-25 22:30:03.304 29787-29787/work.cloud.com.myappcloudwork D/ttt: dispatchTouchEvent in InnerLayout
2018-11-25 22:30:03.305 29787-29787/work.cloud.com.myappcloudwork D/ttt: onInterceptTouchEvent in InnerLayout
2018-11-25 22:30:03.305 29787-29787/work.cloud.com.myappcloudwork D/ttt: onTouchEvent in InnerLayout
2018-11-25 22:30:03.306 29787-29787/work.cloud.com.myappcloudwork D/ttt: onTouchEvent in OuterLinearLayout

可以看到TargetButton的onTouchEvent的方法没有得到执行；而拦截层以上的，以此执行onTouchEvent。

未完，待续。。。下面几张图不太能理解。

 

参考：https://www.cnblogs.com/RGogoing/p/4657722.html

可以移步到https://www.cnblogs.com/huozhong/p/5899687.html，这篇更通俗