The difference between the Android update view function OnDraw () and Dispatchdraw ()

Draw the contents of the View itself , by calling the View.ondraw (canvas) function to implement

Draw your own child through dispatchdraw (canvas) to achieve

The drawing of the view component invokes the draw (canvas canvas) method, in which the drawable background is drawn primarily, the drawable is called SetBounds (), and then the draw (canvas C) method. It is important to note that the actual size of the background drawable affects the size of the view component, and the actual size of the drawable is obtained through Getintrinsicwidth () and Getintrinsicheight (). The size of the view component is equal to the size of the background drawable when the background is relatively large.

After drawing the background, the draw process calls the OnDraw (canvas canvas) method, then the Dispatchdraw (Canvas canvas) method, andDispatchdraw () is mostly distributed to the child components for drawing . We usually rewrite the OnDraw () method when customizing the components. It is noteworthy that the ViewGroup container component is drawn, and when it does not have a background, it calls the Dispatchdraw () method directly, bypassing the draw () method, invoking the draw () method when it has a background, and draw () The method contains a call to the Dispatchdraw () method. So the Dispatchdraw () method , rather than the OnDraw () method, is often overridden to draw something on ViewGroup, or a drawable is customized, the draw (Canvas C) is rewritten, and Getintrinsicwidth (), Getintrinsicheight () method, and then set as background.

The difference between the Android update view function OnDraw () and Dispatchdraw ()