Adding a colored background with text/icon under s

问题:

EDIT: The real problem was that my LinearLayout was wrapped in another layout, which caused the incorrect behavior. The accepted answer by Sanvywell has a better, more complete example of how to draw a color under swiped view than the code snippet I provided in the question.

Now that RecyclerView widget has native support for row swiping with the help of ItemTouchHelper class, I'm attempting to use it in an app where rows will behave similarly to Google's Inbox app. That is, swiping to the left side performs one action and swiping to the right does another.

Implementing the actions themselves was easy using ItemTouchHelper.SimpleCallback's onSwiped method. However, I was unable to find a simple way to set color and icon that should appear under the view that's currently being swiped (like in Google's Inbox app).

To do that, I'm trying to override ItemTouchHelper.SimpleCallback's onChildDraw method like this:

@Override
public void onChildDraw(Canvas c, RecyclerView recyclerView,
                        RecyclerView.ViewHolder viewHolder, float dX, float dY,
                        int actionState, boolean isCurrentlyActive) {
    RecyclerViewAdapter.ViewHolder vh = (RecyclerViewAdapter.ViewHolder) viewHolder;
    LinearLayout ll = vh.linearLayout;

    Paint p = new Paint();
    if(dX > 0) {
        p.setARGB(255, 255, 0, 0);
    } else {
        p.setARGB(255, 0, 255, 0);
    }

    c.drawRect(ll.getLeft(), ll.getTop(), ll.getRight(), ll.getBottom(), p);

    super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
}

Determining the swipe direction from dX and setting the appropriate color works as intended, but the coordinates I get from the ViewHolder always correspond to the place where the first LinearLayout was inflated.

How do I get the correct coordinates for the LinearLayout that's in the currently swiped row? Is there an easier way (that doesn't require to override onChildDraw) to set the background color and icon?

回答1:

I was struggling to implement this feature as well, but you steered me in the right direction.

@Override
public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
    if (actionState == ItemTouchHelper.ACTION_STATE_SWIPE) {
        // Get RecyclerView item from the ViewHolder
        View itemView = viewHolder.itemView;

        Paint p = new Paint();
        if (dX > 0) {
            /* Set your color for positive displacement */

            // Draw Rect with varying right side, equal to displacement dX
            c.drawRect((float) itemView.getLeft(), (float) itemView.getTop(), dX,
                    (float) itemView.getBottom(), p);
        } else {
            /* Set your color for negative displacement */

            // Draw Rect with varying left side, equal to the item's right side plus negative displacement dX
            c.drawRect((float) itemView.getRight() + dX, (float) itemView.getTop(),
                    (float) itemView.getRight(), (float) itemView.getBottom(), p);
        }

        super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
    }
}

回答2:

The accepted answer does a great job of coloring the background, but did not address drawing the icon.

This worked for me because it both set the background color and drew the icon, without the icon being stretched during the swipe, or leaving a gap between the previous and next items after the swipe.

public static final float ALPHA_FULL = 1.0f;

public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
    if (actionState == ItemTouchHelper.ACTION_STATE_SWIPE) {
        // Get RecyclerView item from the ViewHolder
        View itemView = viewHolder.itemView;

        Paint p = new Paint();
        Bitmap icon;

        if (dX > 0) {
            /* Note, ApplicationManager is a helper class I created 
               myself to get a context outside an Activity class - 
               feel free to use your own method */

            icon = BitmapFactory.decodeResource(
                    ApplicationManager.getContext().getResources(), R.drawable.myleftdrawable);

            /* Set your color for positive displacement */
            p.setARGB(255, 255, 0, 0);

            // Draw Rect with varying right side, equal to displacement dX
            c.drawRect((float) itemView.getLeft(), (float) itemView.getTop(), dX,
                    (float) itemView.getBottom(), p);

            // Set the image icon for Right swipe
            c.drawBitmap(icon,
                    (float) itemView.getLeft() + convertDpToPx(16),
                    (float) itemView.getTop() + ((float) itemView.getBottom() - (float) itemView.getTop() - icon.getHeight())/2,
                    p);
        } else {
            icon = BitmapFactory.decodeResource(
                    ApplicationManager.getContext().getResources(), R.drawable.myrightdrawable);

            /* Set your color for negative displacement */
            p.setARGB(255, 0, 255, 0);

            // Draw Rect with varying left side, equal to the item's right side
            // plus negative displacement dX
            c.drawRect((float) itemView.getRight() + dX, (float) itemView.getTop(),
                    (float) itemView.getRight(), (float) itemView.getBottom(), p);

            //Set the image icon for Left swipe
            c.drawBitmap(icon,
                    (float) itemView.getRight() - convertDpToPx(16) - icon.getWidth(),
                    (float) itemView.getTop() + ((float) itemView.getBottom() - (float) itemView.getTop() - icon.getHeight())/2,
                    p);
        }

        // Fade out the view as it is swiped out of the parent's bounds
        final float alpha = ALPHA_FULL - Math.abs(dX) / (float) viewHolder.itemView.getWidth();
        viewHolder.itemView.setAlpha(alpha);
        viewHolder.itemView.setTranslationX(dX);

    } else {
        super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
    }
}

private int convertDpToPx(int dp){
    return Math.round(dp * (getResources().getDisplayMetrics().xdpi / DisplayMetrics.DENSITY_DEFAULT));
}

回答3:

I'm not sure how these solutions (by @Sanvywell, @HappyKatz and @user2410066) are working for you guys but in my case I needed another check in the onChildDraw method.

Looks like ItemTouchHelper keeps ViewHolders of removed rows in case they need to be restored. It's also calling onChildDraw for those VHs in addition to the VH being swiped. Not sure about memory management implications of this behavior but I needed an additional check in the start of onChildDraw to avoid drawing for "fantom" rows.

if (viewHolder.getAdapterPosition() == -1) {
    return;
}

BONUS PART:

I've also wanted to continue drawing as other rows animate to their new positions after a row is swipe deleted, and I couldn't do it within ItemTouchHelper and onChildDraw. In the end I had to add another item decorator to do it. It goes along these lines:

public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
    if (parent.getItemAnimator().isRunning()) {
        // find first child with translationY > 0
        // draw from it's top to translationY whatever you want

        int top = 0;
        int bottom = 0;

        int childCount = parent.getLayoutManager().getChildCount();
        for (int i = 0; i < childCount; i++) {
            View child = parent.getLayoutManager().getChildAt(i);
            if (child.getTranslationY() != 0) {
                top = child.getTop();
                bottom = top + (int) child.getTranslationY();                    
                break;
            }
        }

        // draw whatever you want

        super.onDraw(c, parent, state);
    }
}

UPDATE: I wrote a blog post on recycler view swipe to delete feature. Someone might find it usefull. No 3rd party lib necessary.

blog post git repo

回答4:

HappyKatz solution has a tricky bug. Is there any reason for drawing bitmap when dX==0?? In some cases this causes permanent icon visibility above list item. Also icons become visible above list item when you just touch list item and dX==1. To fix these:

        if (dX > rectOffset) {
            c.drawRect((float) itemView.getLeft(), (float) itemView.getTop(), dX,
                    (float) itemView.getBottom(), leftPaint);
            if (dX > iconOffset) {
                c.drawBitmap(leftBitmap,
                        (float) itemView.getLeft() + padding,
                        (float) itemView.getTop() + ((float) itemView.getBottom() - (float) itemView.getTop() - leftBitmap.getHeight()) / 2,
                        leftPaint);
            }
        } else if (dX < -rectOffset) {
            c.drawRect((float) itemView.getRight() + dX, (float) itemView.getTop(),
                    (float) itemView.getRight(), (float) itemView.getBottom(), rightPaint);
            if (dX < -iconOffset) {
                c.drawBitmap(rightBitmap,
                        (float) itemView.getRight() - padding - rightBitmap.getWidth(),
                        (float) itemView.getTop() + ((float) itemView.getBottom() - (float) itemView.getTop() - rightBitmap.getHeight()) / 2,
                        rightPaint);
            }
        }

回答5:

In order to implement I used the sample code created by Marcin Kitowicz here.

Benefits of this solution:

1. Uses background view with layout bounds instead of creating a Rectangle which will show on top of any Bitmap or Drawable.
2. Uses Drawable image opposed to Bitmap which is easier to implement than needing to convert a Drawable into a Bitmap.

The original implementation code can be found here. In order to implement left swipe I used the inverse left and right positioning logic.

override fun onChildDraw(c: Canvas, recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, dX: Float, dY: Float, actionState: Int, isCurrentlyActive: Boolean) {
if (actionState == ItemTouchHelper.ACTION_STATE_SWIPE) {
    var icon = ContextCompat.getDrawable(context!!, R.drawable.ic_save_24dp)
    var iconLeft = 0
    var iconRight = 0

    val background: ColorDrawable
    val itemView = viewHolder.itemView
    val margin = convertDpToPx(32)
    val iconWidth = icon!!.intrinsicWidth
    val iconHeight = icon.intrinsicHeight
    val cellHeight = itemView.bottom - itemView.top
    val iconTop = itemView.top + (cellHeight - iconHeight) / 2
    val iconBottom = iconTop + iconHeight

    // Right swipe.
    if (dX > 0) {
        icon = ContextCompat.getDrawable(context!!, R.drawable.ic_save_24dp)
        background = ColorDrawable(Color.RED)
        background.setBounds(0, itemView.getTop(), (itemView.getLeft() + dX).toInt(), itemView.getBottom())
        iconLeft = margin
        iconRight = margin + iconWidth
    } /*Left swipe.*/ else {
        icon = ContextCompat.getDrawable(context!!, R.drawable.ic_save_24dp)
        background = ColorDrawable(Color.BLUE)
        background.setBounds((itemView.right - dX).toInt(), itemView.getTop(), 0, itemView.getBottom())
        iconLeft = itemView.right - margin - iconWidth
        iconRight = itemView.right - margin
    }
    background.draw(c)
    icon?.setBounds(iconLeft, iconTop, iconRight, iconBottom)
    icon?.draw(c)
    super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive)
}
}