How to programmatically scroll an HorizontalScrollView

I have an HorizontalScrollView which contains a RelativeLayout. This layout is empty in the XML, and is populated from java in the onCreate.

I would like this scroll view to be initially somewhere in the middle of the RelativeLayout, which is way larger than the screen.

I tried mHorizScrollView.scrollTo(offsetX, 0); which doesn't work. I don't know what's wrong with this.

I could post the code, but it is not really relevant. What matters is that everything is done programatically (has to :s), and that the initial position of the HorizontalScrollView has to be set programmatically.

Thanks for reading. Please tell me if you need more details or if this is 开发者_JAVA百科not clear enough.

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I found that if you extend the HorizontalScrollView and override the onLayout, you can cleanly scroll, after the super call to onLayout:

MyScrollView extends HorizontalScrollView {
    protected void onLayout (boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        this.scrollTo(wherever, 0);
    }
}

EDIT: For scrolling to start or end you can use:

this.fullScroll(HorizontalScrollView.FOCUS_RIGHT/FOCUS_LEFT);

instead of

this.scrollTo(wherever, 0);

---

public void autoSmoothScroll() {

        final HorizontalScrollView hsv = (HorizontalScrollView) view.findViewById(R.id.horiscroll);
        hsv.postDelayed(new Runnable() {
            @Override
            public void run() {
                //hsv.fullScroll(HorizontalScrollView.FOCUS_RIGHT);
                hsv.smoothScrollBy(500, 0);
            }
        },100);
    }

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To test whether it's a timing issue (which I think it is), instead of calling scrollTo() in onStart, call postDelayed() with a Runnable that calls scrollTo, with a delay of 30 or so.

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A better approach would be using the ViewTreeObserver to observe layouts.

View interestedInView;
onCreate(){
  //Code

  //Observe for a layout change
  ViewTreeObserver viewTreeObserver = interestedInView.getViewTreeObserver();
  if (viewTreeObserver.isAlive()) {
    viewTreeObserver.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
      @Override
      public void onGlobalLayout() {
        //REMOVE THE VIEWTREE OBSERVER
        //interestedInView is ready for size and position queries because it has been laid out
      }
    });
  }
}

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The problem is that the view doesn't have a size yet. The Clean way to do this is to implement the onSizeChanged of the ScrollView to send a message to a Handler in your activity to in order to notify the activity that the view has a size and that scrolling is possible.

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Use view.post and write scrollTo(x,y) inside run method. This the way to invalidate view in post method as per android API document.

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The scrollTo function should work. What is the layout_width of the HSV, and the view inside of it?

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The onSizeChanged function should work. What you fail to understand is that the onSizeChanged should send a message to a Handler of your activity and not any callback function, because a handler will execute code in the UI thread. You cannot do UI operations outside it. Have a look at handlers.

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Use Kotlin extension function.

inline fun <T : View> T.afterMeasured(crossinline f: T.() -> Unit) {
viewTreeObserver.addOnGlobalLayoutListener(object : ViewTreeObserver.OnGlobalLayoutListener {
    override fun onGlobalLayout() {
        if (measuredWidth > 0 && measuredHeight > 0) {
            viewTreeObserver.removeOnGlobalLayoutListener(this)
            f()
        }
    }
})

}

Usage:

mHorizontalScrollView.afterMeasured {
        var scrollTo = 0
        val count = (layout.svList.getChildAt(0) as LinearLayout)
            .childCount

        if(index < count){
            val child = (layout.svList.getChildAt(0) as LinearLayout)
                .getChildAt(index)

            scrollTo = child.width

        }

        Log.d(TAG, "scrollToComment: $scrollTo")

        mHorizontalScrollView.scrollTo(scrollTo, 0)
    }