Custom Control (3): view rendering principle, view rendering

Custom Control (3): view rendering principle, view rendering
To customize the UI control, you must inherit the View class or View subclass and reload some methods in the View class. You do not have to reload them, but at least need to reload onDraw ().

Category	Method	Description
Creation	Constructors
	OnFinishInflate ()	This method is called when View and all its sub-objects are imported from XML.
Layout	OnMeasure (int, int)	View will call this method to confirm the size of itself and all sub-objects
	OnLayout (boolean, int, int)	This method is called when the View needs to allocate the size and position of all sub-objects.
	OnSizeChanged (int, int)	This method is called when the View Size changes.
Drawing	OnDraw (Canvas)	This method is called when a View wants to draw its content
Event processing	OnKeyDown (int, KeyEvent)	This method is called when a new key event occurs.
	OnKeyUp (int, KeyEvent)	This method is called when a key release event occurs.
	OnMotionEvent (MotionEvent)	This method is called when an action event (such as touch) occurs.
Focus	OnFocusChanged (boolean, int)	This method is called when the View gets or loses focus.
Attaching	OnAttachedToWindow ()	This method is called when a View is attached to a form.
	OnDetachedFromWindow ()	This method is called when a View leaves its form.

View Painting Process: onAttachedToWindow-> onMeasrue-> onSizeChanged-> onLayout-> onDraw
Draw View in Activity: Use setContentView () reference the root node of the input Hierarchy Tree-> Activity is activated and focused-> request the root node to calculate and draw the tree-> ViewGroup layout based on its own valid space and LayoutParams required by the child View child view, and call the Draw () method of the sub-view to Draw it.