Android：可以在绘制视图之前更改视图的高度吗？

Question

I'd like to do something like the following:

rootLayout.getLayoutParams().height = 100;

Currently I have this line in my 'loadData' method. The problem is - 'layoutParams' seems to be null until sometime after 'loadData' has been called (but before it is displayed obviously).

Is there somewhere I can place this line where the layoutParams will have been instantiated, but still be before the view is shown for the first time?

Answer 1

    rootLayout.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
                    rootLayout.getViewTreeObserver()
                            .removeOnGlobalLayoutListener(this);
                } else {
                    rootLayout.getViewTreeObserver()
                            .removeGlobalOnLayoutListener(this);
                }
                rootLayout.getLayoutParams().height = 100;
                rootLayout.requestLayout();
            }
        });

Answer 2

You should consider to set layoutParams of this view as

LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT, 100));
 rootLayout.setLayoutParams(lp);

So You can set layoutParams height as 100 and assuming that your parent view as linear layout ,if it's not, then you should use its layoutparams

Answer 3

on the docs you can check all the callbacks the view have that you can override https://developer.android.com/reference/android/view/View.html

if your view is inside an XML layout with the LayoutParams specified in there, you can/should put your code inside onFinishInflate

   @Override
   public void onFinishInflate() {
   }

if you're doing all this programmatically, you can override the layout pass

@Override
public void onLayout (boolean changed, int left, int top, int right, int bottom){
    // be carefull that this get's called several times
}

alternatively (a nicer approach in my opinion), you can trick the onMeasure of your view to have the size you want. For example, to have a view with a maxWidth

   @Override
   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
      // apply max width
      int measuredWidth = MeasureSpec.getSize(widthMeasureSpec);
      if (maxWidth > 0 && maxWidth < measuredWidth) {
         int measureMode = MeasureSpec.getMode(widthMeasureSpec);
         widthMeasureSpec = MeasureSpec.makeMeasureSpec(maxWidth, measureMode);
      }
      super.onMeasure(widthMeasureSpec, heightMeasureSpec);
   }