private ConstraintLayout constraintLayout;
constraintLayout=findViewById(R.id.screen_test);
constraintLayout.measure(0,0);
Log.i(TAG,"onCreate:"+constraintLayout.getMeasuredHeight()+","+constraintLayout.getMeasuredWidth());

0所對應的 MeasureSpec

現在知道了傳遞的0並不是簡單的一個0，它符合著 MeasureSpec 規範。
將0解包後，所對應的 SpecMode = 0，SpecSize = 0.
SpecMode 0 對應的模式為 UNSPECIFIED.
UNSPECIFIED的

The parent has not imposed any constraint on the child. It can be whatever size it wants.
父容器不會對子元素加以任何約束，子元素可以是任何大小。