CODEWITHSUNDEEP
javaandroid
Rajesh Patil
Rajesh Patil

Reputation: 73

How to scroller scroll smoothly?

My problem is when I'm using scroller and draw canvas on it. It will scroll smoothly but when I draw bitmap + canvas the scroller scroll very slow means it is heavy to scroll thats why it scroll very slow fashion.

How to solve this problem?

Upvotes: 0

Views: 1758

Answers (1)

user647826
user647826

Reputation:

I have no experience with OpenGL nor accelerometer, but swipe (called fling in Android's API) is not hard to achieve. First thing you need when making such a custom View, is implementing a GestureDetector and call its onTouchEvent() in your view's onTouchEvent()

GestureDetector mGD = new GestureDetector(getContext(),
                                        new SimpleOnGestureListener() {

    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2,
                                float distanceX, float distanceY) {
        // beware, it can scroll to infinity
        scrollBy((int)distanceX, (int)distanceY);
        return true;
    }

    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float vX, float vY) {
        mScroller.fling(getScrollX(), getScrollY(),
                -(int)vX, -(int)vY, 0, (int)mMaxScrollX, 0, (int)mMaxScrollY);
        invalidate(); // don't remember if it's needed
        return true;
    }

    @Override
    public boolean onDown(MotionEvent e) {
        if(!mScroller.isFinished() ) { // is flinging
            mScroller.forceFinished(true); // to stop flinging on touch
        }
        return true; // else won't work
    }
});

@Override
public boolean onTouchEvent(MotionEvent event) {
    return mGD.onTouchEvent(event);
}

While OnGestureListener.onScroll() calls directly View.scrollBy(), for the onFling() method you'll need a Scroller.

Scroller is a simple object that, as reference says, encapsulates scrolling. It can be used for continuous scrolling or to react to flings. Scroller.fling() begin a "simulation" of fling scroll inside itself, and by watching it you can copy its smoothness with a continuous redrawing animation:

@Override
protected void onDraw(Canvas canvas) {
    // ....your drawings....

    // scrollTo invalidates, so until animation won't finish it will be called
    // (used after a Scroller.fling() )
    if(mScroller.computeScrollOffset()) {
        scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
    }
}

that is, until animation is running, calculate the point we reached and scroll there.

As a last note: remember to return true in your OnGestureListener.onDown(), even if you don't want to do anything on down, or it won't work.

And be careful, because Scroller in Android 2.2 has a bug for which the fling animation will not actually end even if it reaches the limits you passed as arguments (yet computed offset respects them, so it won't actually move).

Upvotes: 2

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