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Android: Detect when ScrollView stops scrolling

Asked 2011-11-18T11:39:42.043
93

I'm using a ScrollView in Android and where the visible portion of the ScrollView is the same size as one of the cells inside the Scrollview. Every "cell" is the same height. So what I am trying to do is snap into position after the ScrollView has been scrolled.

Currently I am detecting when the user has touched the ScrollView and when they've started scrolling and working it out from there, but it is quite buggy. It also needs to work when the user just flicks it and it scrolls and then decelerates.

On iPhone there is a function that is something like didDecelerate and there I can do any code I want when the ScrollView has finished scrolling. Is there such a thing with Android? Or is there some code I could look at to figure out a better way of doing it?

I've looked over the Android docs and could not find anything like that.

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3 Answers

24

Here is yet another fix to the, IMHO, missing OnEndScroll event bug in the ScrollView.

Its inspired by hambonious answer. Simply drop this class into your project (change package to match your own) and use the below xml

package com.thecrag.components.ui;

import android.content.Context;
import android.util.AttributeSet;
import android.widget.ScrollView;

public class ResponsiveScrollView extends ScrollView {

    public interface OnEndScrollListener {
        public void onEndScroll();
    }

    private boolean mIsFling;
    private OnEndScrollListener mOnEndScrollListener;

    public ResponsiveScrollView(Context context) {
        this(context, null, 0);
    }

    public ResponsiveScrollView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public ResponsiveScrollView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    public void fling(int velocityY) {
        super.fling(velocityY);
        mIsFling = true;
    }

    @Override
    protected void onScrollChanged(int x, int y, int oldX, int oldY) {
        super.onScrollChanged(x, y, oldX, oldY);
        if (mIsFling) {
            if (Math.abs(y - oldY) < 2 || y >= getMeasuredHeight() || y == 0) {
                if (mOnEndScrollListener != null) {
                    mOnEndScrollListener.onEndScroll();
                }
                mIsFling = false;
            }
        }
    }

    public OnEndScrollListener getOnEndScrollListener() {
        return mOnEndScrollListener;
    }

    public void setOnEndScrollListener(OnEndScrollListener mOnEndScrollListener) {
        this.mOnEndScrollListener = mOnEndScrollListener;
    }

}

again changing the package name to match your project

<com.thecrag.components.ui.ResponsiveScrollView
        android:id="@+id/welcome_scroller"
answered 2013-01-20T16:53:20.223
9

I subclassed (Horizontal)ScrollView and did something like this:

@Override
protected void onScrollChanged(int x, int y, int oldX, int oldY) {
    if (Math.abs(x - oldX) > SlowDownThreshold) {  
        currentlyScrolling = true;
    } else {
        currentlyScrolling = false;
        if (!currentlyTouching) {
            //scrolling stopped...handle here
        }
    }
    super.onScrollChanged(x, y, oldX, oldY);
}

I used a value of 1 for the SlowDownThreshold since it always seems to be the difference of the last onScrollChanged event.

In order to make this behave correctly when dragging slowly, I had to do this:

@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            currentlyTouching = true;
    }
    return super.onInterceptTouchEvent(event);
}

@Override
public boolean onTouch(View view, MotionEvent event) {
    switch (event.getAction()) {
        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_CANCEL:
            currentlyTouching = false;
            if (!currentlyScrolling) {
                //I handle the release from a drag here
                return true;
            }
    }
    return false;
}
answered 2012-03-26T17:20:40.557
2

Try taking a look at this question here on StackOverflow - it's not exactly the same as your question, but it gives an idea on how you can manage the scroll event of a ScrollView.

Basicly you need to create your own CustomScrollView by extending ScrollView and override onScrollChanged(int x, int y, int oldx, int oldy). Then you need to reference this in your layout file instead of the standard ScrollView like com.mypackage.CustomScrollView.

answered 2011-11-18T11:52:41.587

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