Android: get height of a view before it´s drawn

问题

For an animation I need to know the height from a View. The Problem is, that the getHeight() method allways return 0 unless the View is drawn. So is there any way to get height without drawing it?

In this case the View is a LinearLayout.

EDIT: I try to adapt the expand Animation from https://github.com/Udinic/SmallExamples/blob/master/ExpandAnimationExample/src/com/udinic/expand_animation_example/ExpandAnimation.java

With it I want to expand some more informations for a list item. I wasn´t able to achieve the same effect via xml. At the moment the Animation only works when you know the layout size before drawing it.

回答1:

Sounds like you want to get the height but hide the view before it is visible.

Have the visibility in the view set to visible or invisible to start with(just so that a height is created). Don't worry we will change it to invisible/gone in the code as shown below:

private int mHeight = 0;
private View mView;

class...

// onCreate or onResume or onStart ...
mView = findViewByID(R.id.someID);
mView.getViewTreeObserver().addOnGlobalLayoutListener( 
    new OnGlobalLayoutListener(){

        @Override
        public void onGlobalLayout() {
            // gets called after layout has been done but before display
            // so we can get the height then hide the view


            mHeight = mView.getHeight();  // Ahaha!  Gotcha

            mView.getViewTreeObserver().removeGlobalOnLayoutListener( this );
            mView.setVisibility( View.GONE );
        }

});

回答2:

I had a similar issue with a similar situation.

I had to create an anmiation for which I required the height of the view that is subject to the animation. Within that view, which is a LinearLayout may be child view of type TextView. That TextView is multi line and the number of lines actually required varies.

Whatever I did I just got the measured height for the view as if the TextView has just one line to fill. No wonder this worked fine every time when the text happend to be short enough for a single line, but it failed when the text was longer than on line.

I considered this answer: https://stackoverflow.com/a/6157820/854396 But that one did not work too well for me because I am not able to access the embedded TextView directly from here. (I could have iterated though the tree of child views though.)

Have a look at my code as it works for now:

view is the view that is to be animated. It is a LinearLayout (The final solution will be a bit more type save here) this is a custom view that contains view and inherits from LinearLayout too.

   private void expandView( final View view ) {

      view.setVisibility(View.VISIBLE);

      LayoutParams parms = (LayoutParams) view.getLayoutParams();
      final int width = this.getWidth() - parms.leftMargin - parms.rightMargin;

      view.measure( MeasureSpec.makeMeasureSpec(width, MeasureSpec.AT_MOST),
              MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));

      final int targetHeight = view.getMeasuredHeight();

      view.getLayoutParams().height = 0;

      Animation anim = new Animation() {
         @Override
         protected void applyTransformation( float interpolatedTime, Transformation trans ) {
            view.getLayoutParams().height =  (int) (targetHeight * interpolatedTime);
            view.requestLayout();
         }

         @Override
         public boolean willChangeBounds() {
            return true;
         }
      };

      anim.setDuration( ANIMATION_DURATION );
      view.startAnimation( anim );
   }

This was nearly it but I made another mistake. Within the view hierarchy there are two custom views involved which are subclasses of LinearLayout and their xml is merged into with a merge tag as xml root tag. Within one of these merge tags I overlooked to set the android:orientation attribute to vertical. That did not bother too much for the layout itself, because within this merged ViewGroup was just one child ViewGroup and therfore I could not actually see the wrong orientation on screen. But it was there and sort of broke this layout measurement logic a bit.

In addition to the above it may be required to get rid of all paddings associated with LinearLayouts and subclasses within the view hierarchy. Replace them by margins, even if you have to wrap another layout around it to make it look the same.

回答3:

Technically, you can call measure method on the view and then get its height via getMeasureHeight. See this for more info: https://developer.android.com/guide/topics/ui/how-android-draws.html. You will need to give it a MeasureSpec though.

But in reality, the view's size is influenced by its parent layout, so you may get a different size than when it's actually drawn.

Also, you may try using RELATIVE_TO_SELF values in your animations.

回答4:

static void getMeasurments(View v) {

    v.measure(View.MeasureSpec.makeMeasureSpec(PARENT_VIEW.getWidth(), 
      View.MeasureSpec.EXACTLY),
         View.MeasureSpec.makeMeasureSpec(0, 
      View.MeasureSpec.UNSPECIFIED));

    final int targetHeight = v.getMeasuredHeight();
    final int targetWidth = v.getMesauredWidth();
}

回答5:

just measure it yourself if the parent does not determine its size:

here is a kotlin extension on view to do it for you always:

fun View.getMeasurments(): Pair<Int, Int> {
    measure(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED)
    val width = measuredWidth
    val height = measuredHeight
    return width to height
}

回答6:

Ok, regarding the updated post, here is what will help you: Animation#initialize method. You should just put initialization there instead of the constructor, and you'll have all the sizes you need there.

回答7:

You could try to start with the View visible, and then add something like this:

view.post(new Runnable() {      
    @Override
    public void run() {
        // hide view here so that its height has been already computed
        view.setVisibility(View.GONE);
    }
});

Now when you will call view.getHeight() it should return the height you expect.

I'm not sure if it's really a good way to do it, but at least it should work.

来源：https://stackoverflow.com/questions/9575706/android-get-height-of-a-view-before-it%c2%b4s-drawn

标签

android

layout

view

height