How can you tell when a layout has been drawn

Question

I have a custom view that draws a scrollable bitmap to the screen  In order to initialize it  i need to pass in the size in pixels of the parent layout object  But during the onCreate and onResume functions  the Layout has not been drawn yet  and so layout getMeasuredHeight   returns 0    As a workaround  i have added a handler to wait one second and then measure  This works  but its sloppy  and I have no idea how much i can trim the time before I end up before the layout gets drawn    What I want to know is  how can I detect when a layout gets drawn  Is there an event or callback

User · Answer

When onMeasure is called the view gets its measured width height  After this  you can call layout getMeasuredHeight

User · Answer

Better with kotlin extension functions  inline fun View waitForLayout crossinline yourAction     - gt  Unit        val vto   viewTreeObserver     vto addOnGlobalLayoutListener object   ViewTreeObserver OnGlobalLayoutListener           override fun onGlobalLayout                 when                   vto isAlive - gt                        vto removeOnGlobalLayoutListener this                      yourAction                                     else - gt  viewTreeObserver removeOnGlobalLayoutListener this

User · Answer

A really easy way is to simply call post   on your layout  This will run your code the next step  after your view has already been created   YOUR LAYOUT post  new Runnable          Override     public void run             int width    YOUR LAYOUT getMeasuredWidth            int height   YOUR LAYOUT getMeasuredHeight

User · Answer

Another answer is  Try checking the View dimensions at onWindowFocusChanged

User · Answer

You can add a tree observer to the layout  This should return the correct width and height  onCreate   is called before the layout of the child views are done  So the width and height is not calculated yet  To get the height and width  put this on the onCreate   method       final LinearLayout layout    LinearLayout  findViewById R id YOUR VIEW ID       ViewTreeObserver vto   layout getViewTreeObserver         vto addOnGlobalLayoutListener  new OnGlobalLayoutListener               Override          public void onGlobalLayout         if  Build VERSION SDK INT  gt   Build VERSION CODES JELLY BEAN                        layout getViewTreeObserver                                removeOnGlobalLayoutListener this                     else                       layout getViewTreeObserver                                removeGlobalOnLayoutListener this                                 int width    layout getMeasuredWidth                int height   layout getMeasuredHeight

User · Answer

An alternative to the usual methods is to hook into the drawing of the view   OnPreDrawListener is called many times when displaying a view  so there is no specific iteration where your view has valid measured width or height  This requires that you continually verify  view getMeasuredWidth    lt   0  or set a limit to the number of times you check for a measuredWidth greater than zero   There is also a chance that the view will never be drawn  which may indicate other problems with your code   final View view    ACQUIRE REFERENCE      Must be declared final for inner class ViewTreeObserver viewTreeObserver   view getViewTreeObserver    viewTreeObserver addOnPreDrawListener new ViewTreeObserver OnPreDrawListener          Override     public boolean onPreDraw             if  view getMeasuredWidth    gt  0                     view getViewTreeObserver   removeOnPreDrawListener this               int width   view getMeasuredWidth                int height   view getMeasuredHeight                  Do something with width and height here                    return true     Continue with the draw pass  as not to stop it

User · Answer

To avoid deprecated code and warnings you can use   view getViewTreeObserver   addOnGlobalLayoutListener          new ViewTreeObserver OnGlobalLayoutListener                  SuppressWarnings  deprecation                Override             public void onGlobalLayout                     if  Build VERSION SDK INT  gt   Build VERSION CODES JELLY BEAN                        view getViewTreeObserver                                removeOnGlobalLayoutListener this                     else                       view getViewTreeObserver                                removeGlobalOnLayoutListener this                                     yourFunctionHere

User · Answer

Simply check it by calling post method on your layout or view  view post  new Runnable           Override      public void run                your layout is now drawn completely   use it here

[android] How can you tell when a layout has been drawn?

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