View drawing process analysis

setContentView() What did you do

 

We know that onCreate（） In the method setContentView（） The method is to xml The file resolves to DecorView On , that DecorView When was it displayed on the screen ？

We all know activity In the life cycle of onResume（） A lot of work , and onResume（） As shown in the figure above . stay ActivityThread in ,handleResumeActivity（） Methods not only call performActivity（） Method is finally implemented on onResume() Method call , The following operations are also carried out . 

 

  and ViewManger It's an interface , The real thing is WindowMangerImpl

  The real call is WindowManagerGlobal Of addView() Method

  Method ViewRootImpl

mViews.add(view);  //DecorView

mRoots.add(root);  //ViewRootImpl

 mParams.add(wparams) //WindowManager.LayoutParams

  root.setView(view, wparams, panelParentView);// take view and viewRootImpl Binding

Go find ViewRootImpl Of setView() Method , The most important thing is the internal call requestLayout() Method

  stay requestLayout() In the method , First of all be checkThread() Check whether the current thread is the main thread , And then execute scheduleTraversals（） Method for real rendering .

 

 scheduleTraversals（） Pass through mTraversalRunable perform doTraversal() Method

Final execution to performTraversals() Method , draw view Is executed in this method .

 

performTraversals（） The method is very long. , Did a lot of things

1. windowSizeMayChange |= measureHierarchy(host, lp, res, desiredWindowWidth, desiredWindowHeight); Notes also explain , Is to ask for the desired size , That is, the predicted quantity

Only wrap_content The situation that needs to be negotiated

a. First, through res.getValue Give an initial value to measure

b.performMeasure()

c.if ((host.getMeasuredWidthAndState()&View.MEASURED_STATE_TOO_SMALL) == 0)

If the measurement result is satisfactory , Is set to true

d. If not satisfied if Conditions , The modified baseSize,

 baseSize = (baseSize+desiredWindowWidth)/2,

Re engage performMeasure()

e. If not satisfied , The window width and height are assigned to , For the third time performMeasure()

 

  If windowSizeMayChange = true, It means that measurement is still needed

 2. relayoutResult = relayoutWindow(params, viewVisibility, insetsPending);// Layout window Actually WMS In the called

 3.performMeasure(childWidthMeasureSpec,childHeightMeasureSpec);// Measurement of the number of controls （ At most 4 Time performMeasure()）

 

perform view Of itself measure() Method ,measure() Methods must call setMesureDemension() Method

4.performLayout(lp,mWidth,mHeight)

Allied , call view Of layout() Method  

 

  Can be done layoutChange Listening in , And learn about the changes

If it is view, You need to add your own padding, If it's a container , You need to add Margin

5.performDraw();// draw

 

performDraw（） Method is called internally draw() 

 scrollToRectOrFocus(null, false) Calculate scrolling , Such as the pop-up of the keyboard ？

There are two cases of drawing ： Hardware acceleration or Software acceleration  

Software and hardware drawing process 、 difference ？ To be added   Better hardware rendering （ The software drawing will draw everything ）

Whatever it is , Will be called view Of draw() Method , Well known （ background ,dispatchDraw() The process of ）, Custom controls generally do not override this method

 canvas There are also software and hardware

measure() Method is to measure and determine the size of the child control ,layout() In the onLayout() The method is to determine the current view Position in the parent control

  stay ViewRootImpl Of setView() In the method , Other operations were also performed . The purpose is to add windows to WMS On 、

Give yourself the current view Set up parent

 

stay ViewRootImpl Constructor

mThread = Threag.currentThread() // Get the thread that created it

mDirty = new Rect() // Dirty areas

mAttachInfo = new View.AttachInfo() // Save some information about the current window

WindowMangerImpl determine View Which parent window does it belong to

WindowManagerGlobal  Manage the entire process All window information

ViewRootImpl yes WindowManagerGlobal The actual operator of , Operate your own window