Panel glitching and stopping in the middle every so often

[PhpXp]

Since I first tried this library I had a problem that every 1 in 50 times or so the panel glitched and got stuck in the middle even though I had no anchor point set.

Example: https://gfycat.com/SeparateInformalAmericanavocet

ignore the View animations it's just an example I think it happens when I try to expand the panel very quickly.

After some debugging I noticed the issue is in the ViewDragHelper:

public boolean continueSettling(boolean deferCallbacks) {
    // Make sure, there is a captured view
    if (mCapturedView == null) {
        return false;
    }
    if (mDragState == STATE_SETTLING) {
        boolean keepGoing = mScroller.computeScrollOffset();
        final int x = mScroller.getCurrX();
        final int y = mScroller.getCurrY();
        final int dx = x - mCapturedView.getLeft();
        final int dy = y - mCapturedView.getTop();

        if(!keepGoing && dy != 0) { //add this 5 lines
            //Invalid drag state
            mCapturedView.setTop(0);
            return true;
        }
        // ...

I don't know why it happens but everytime it does, keepGoing is false but dy is a very large negative number (around -600) instead of 0. The correct behaviour is that when y is getting close to 0, so should dy.

So adding those 5 lines fixes the glitching but it's really just a workaround.

I have Android 5.1.1 on an Z3 Compact, but the issue was already present in 5.0.2.

Does anyone else experience this glitch?

[qbraet]

I was just about to create a ticket with almost the same problem.
I thought it was caused by the recyclerview I was using in the panel (I use the latest master version, so should support this), but maybe it's a more general issue.

For me, this seems to happen when, while swiping down, your finger moves over to another cell in the recyclerview. If your finger stays in the same cell while swiping, this issue doesn't seem to appear.
It also doesn't happen if you swipe on the empty space below recyclerview cells (e.g. when there is only 1 cell and lots of space left underneath it). So it seems that "crossing views" while swiping causes my error, but I'm not 100% sure about that

[PhpXp]

I just want to say that I've been using the mentioned fix for the last two months with no problems. It fixes the bug completely and brings no other errors. The panel hasn't gotten stuck since.

I really feel like this fix should be implemented. I can make a pull request, but ^{I have yet to learn how to do that ...}

[Shusshu]

I also encounter this bug.

[Shusshu]

@PhpXp Can you try and make a pull request? it's very easy
https://help.github.com/articles/creating-a-pull-request/

In short:

• fork
• create branch "issue-525"
• commit fix to branch
• push to your github repo
• go to github and press the pull request button

[JShortwhile]

These 5 lines did not worked for me. But if I delete the second condition in this line:

if ((ady > dragSlop && adx > ady) || !isViewUnder(mDragView, (int) mInitialMotionX, (int) mInitialMotionY)) {

in the onInterceptTouchEvent() function, everything works fine.

Do you know why is there such a condition?

[PhpXp]

Check your imports, maybe you are using the default Android provided ViewDragHelper.

Also, those 5 lines are really a workaround, not a fix. I never found out why it even gets into that state. Maybe your code is the real fix, I'll take a look at it.

[kshitijcode]

I am too facing the issue. It gets stuck while scrolling back up or down particularly if I do an entire "drag" then just a "fling".

[dmitriigriazin]

Hi! I'm facing this bug on all platforms api 16+.

As @qbraet said, "view crossing" causes it, I do confirm that, the same behavior.
As a dirty hack I tried to put a transparent clickable view over all the panel layout - did not worked:D Seems like currently we have to fork anyway.

I have a guess, that the coodinate returned by mCapturedView.getTop() is wrong, mb it is relative to the mCapturedView itself or somewhat else, not to the hosting panel. Going to check it out soon.

UPD. Finally found it. continueSettling has nothing to do with that. You will not believe it, but the reason is that the author just really prohibited the dragging, when the "view crossing happens" or dx > dy.

SlidingUpPanelLayout.java

@Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        // ....
        switch (action) {
            // ....
            case MotionEvent.ACTION_MOVE: {
                final float adx = Math.abs(x - mInitialMotionX);
                final float ady = Math.abs(y - mInitialMotionY);
                final int dragSlop = mDragHelper.getTouchSlop();

                /*if ((ady > dragSlop && adx > ady) || !isViewUnder(mDragView, (int) mInitialMotionX, (int) mInitialMotionY)) {
                    mDragHelper.cancel();
                    mIsUnableToDrag = true;
                    return false;
                }*/
                break;
            }

See that commented condition. It solves the issue.

Why it happened and what should we learn from that:
This issue will happen really when the scroll is fast. The speed of gestures updates is limited. The author probably expected, that the code will get every drag update and will calculate if the pointer is over the view. However, if the swipe speed is high, the delta value will be high, and the problem rises: view is not positioned to the right place yet, but the new pointer's coordinates are far from this view, so !isViewUnder() is true.

Need also to fix the behavior, when dx > dy , so the cancellation happens, rather than the panel freeze.

Community vs bugs 1 : 0

PS
goona make pull request soon

[Shusshu]

a new release on the way? :)

[kshitijcode]

Still doesnt work. When I do a really long drag the panel doesnt go up .