我正在尝试将一些 iOS 功能移植到 Android。

我打算创建一个表格，向左滑动会显示 2 个按钮:编辑和删除。

我一直在玩它，我知道我非常接近。秘诀在于方法 OnChildDraw。

我想绘制一个适合文本删除的矩形，然后使用它们各自的背景颜色在其旁边绘制编辑文本。单击时剩余的空白应将该行恢复到其初始位置。

我已经设法在用户向两侧滑动时绘制背景，但我不知道如何添加监听器，一旦滑动到一侧，拖动功能就会开始出现异常。

我正在研究 Xamarin，但也接受纯 Java 解决方案，因为我可以轻松地将它们移植到 c#。

    public class SavedPlacesItemTouchHelper : ItemTouchHelper.SimpleCallback
    {
        private SavedPlacesRecyclerviewAdapter adapter;
        private Paint paint = new Paint();
        private Context context;

        public SavedPlacesItemTouchHelper(Context context, SavedPlacesRecyclerviewAdapter adapter) : base(ItemTouchHelper.ActionStateIdle, ItemTouchHelper.Left)
        {
            this.context = context;
            this.adapter = adapter;
        }

        public override bool OnMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target)
        {
            return false;
        }

        public override void OnSwiped(RecyclerView.ViewHolder viewHolder, int direction)
        {
        }

        public override void OnChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, bool isCurrentlyActive)
        {
            float translationX = dX;
            View itemView = viewHolder.ItemView;
            float height = (float)itemView.Bottom - (float)itemView.Top;

            if (actionState == ItemTouchHelper.ActionStateSwipe && dX <= 0) // Swiping Left
            {
                 translationX = -Math.Min(-dX, height * 2);
                paint.Color = Color.Red;
                RectF background = new RectF((float)itemView.Right + translationX, (float)itemView.Top, (float)itemView.Right, (float)itemView.Bottom);
                c.DrawRect(background, paint);

                //viewHolder.ItemView.TranslationX = translationX;
            }
            else if (actionState == ItemTouchHelper.ActionStateSwipe && dX > 0) // Swiping Right
            {
                translationX = Math.Min(dX, height * 2);
                paint.Color = Color.Red;
                RectF background = new RectF((float)itemView.Right + translationX, (float)itemView.Top, (float)itemView.Right, (float)itemView.Bottom);
                c.DrawRect(background, paint);
            }

            base.OnChildDraw(c, recyclerView, viewHolder, translationX, dY, actionState, isCurrentlyActive);
        }
    }
}

这是我目前拥有的。

如果您知道如何添加听众或有任何建议，请发表评论!

更新:

我刚刚意识到双击该行的白色剩余空间已经将该行恢复到其初始状态。虽然不是一个水龙头:(

最佳答案

我遇到了同样的问题，并试图在网上找到解决方案。大多数解决方案使用两层方法(一层 View 项，另一层按钮)，但我只想坚持使用 ItemTouchHelper。最后，我想出了一个可行的解决方案。请在下方查看。

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;
import android.graphics.Rect;
import android.graphics.RectF;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.helper.ItemTouchHelper;
import android.util.Log;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Queue;

public abstract class SwipeHelper extends ItemTouchHelper.SimpleCallback {

    public static final int BUTTON_WIDTH = YOUR_WIDTH_IN_PIXEL_PER_BUTTON
    private RecyclerView recyclerView;
    private List<UnderlayButton> buttons;
    private GestureDetector gestureDetector;
    private int swipedPos = -1;
    private float swipeThreshold = 0.5f;
    private Map<Integer, List<UnderlayButton>> buttonsBuffer;
    private Queue<Integer> recoverQueue;

    private GestureDetector.SimpleOnGestureListener gestureListener = new GestureDetector.SimpleOnGestureListener(){
        @Override
        public boolean onSingleTapConfirmed(MotionEvent e) {
            for (UnderlayButton button : buttons){
                if(button.onClick(e.getX(), e.getY()))
                    break;
            }

            return true;
        }
    };

    private View.OnTouchListener onTouchListener = new View.OnTouchListener() {
        @Override
        public boolean onTouch(View view, MotionEvent e) {
            if (swipedPos < 0) return false;
            Point point = new Point((int) e.getRawX(), (int) e.getRawY());

            RecyclerView.ViewHolder swipedViewHolder = recyclerView.findViewHolderForAdapterPosition(swipedPos);
            View swipedItem = swipedViewHolder.itemView;
            Rect rect = new Rect();
            swipedItem.getGlobalVisibleRect(rect);

            if (e.getAction() == MotionEvent.ACTION_DOWN || e.getAction() == MotionEvent.ACTION_UP ||e.getAction() == MotionEvent.ACTION_MOVE) {
                if (rect.top < point.y && rect.bottom > point.y)
                    gestureDetector.onTouchEvent(e);
                else {
                    recoverQueue.add(swipedPos);
                    swipedPos = -1;
                    recoverSwipedItem();
                }
            }
            return false;
        }
    };

    public SwipeHelper(Context context, RecyclerView recyclerView) {
        super(0, ItemTouchHelper.LEFT);
        this.recyclerView = recyclerView;
        this.buttons = new ArrayList<>();
        this.gestureDetector = new GestureDetector(context, gestureListener);
        this.recyclerView.setOnTouchListener(onTouchListener);
        buttonsBuffer = new HashMap<>();
        recoverQueue = new LinkedList<Integer>(){
            @Override
            public boolean add(Integer o) {
                if (contains(o))
                    return false;
                else
                    return super.add(o);
            }
        };

        attachSwipe();
    }


    @Override
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
        return false;
    }

    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
        int pos = viewHolder.getAdapterPosition();

        if (swipedPos != pos)
            recoverQueue.add(swipedPos);

        swipedPos = pos;

        if (buttonsBuffer.containsKey(swipedPos))
            buttons = buttonsBuffer.get(swipedPos);
        else
            buttons.clear();

        buttonsBuffer.clear();
        swipeThreshold = 0.5f * buttons.size() * BUTTON_WIDTH;
        recoverSwipedItem();
    }

    @Override
    public float getSwipeThreshold(RecyclerView.ViewHolder viewHolder) {
        return swipeThreshold;
    }

    @Override
    public float getSwipeEscapeVelocity(float defaultValue) {
        return 0.1f * defaultValue;
    }

    @Override
    public float getSwipeVelocityThreshold(float defaultValue) {
        return 5.0f * defaultValue;
    }

    @Override
    public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
        int pos = viewHolder.getAdapterPosition();
        float translationX = dX;
        View itemView = viewHolder.itemView;

        if (pos < 0){
            swipedPos = pos;
            return;
        }

        if(actionState == ItemTouchHelper.ACTION_STATE_SWIPE){
            if(dX < 0) {
                List<UnderlayButton> buffer = new ArrayList<>();

                if (!buttonsBuffer.containsKey(pos)){
                    instantiateUnderlayButton(viewHolder, buffer);
                    buttonsBuffer.put(pos, buffer);
                }
                else {
                    buffer = buttonsBuffer.get(pos);
                }

                translationX = dX * buffer.size() * BUTTON_WIDTH / itemView.getWidth();
                drawButtons(c, itemView, buffer, pos, translationX);
            }
        }

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

    private synchronized void recoverSwipedItem(){
        while (!recoverQueue.isEmpty()){
            int pos = recoverQueue.poll();
            if (pos > -1) {
                recyclerView.getAdapter().notifyItemChanged(pos);
            }
        }
    }

    private void drawButtons(Canvas c, View itemView, List<UnderlayButton> buffer, int pos, float dX){
        float right = itemView.getRight();
        float dButtonWidth = (-1) * dX / buffer.size();

        for (UnderlayButton button : buffer) {
            float left = right - dButtonWidth;
            button.onDraw(
                    c,
                    new RectF(
                            left,
                            itemView.getTop(),
                            right,
                            itemView.getBottom()
                    ),
                    pos
            );

            right = left;
        }
    }

    public void attachSwipe(){
        ItemTouchHelper itemTouchHelper = new ItemTouchHelper(this);
        itemTouchHelper.attachToRecyclerView(recyclerView);
    }

    public abstract void instantiateUnderlayButton(RecyclerView.ViewHolder viewHolder, List<UnderlayButton> underlayButtons);

    public static class UnderlayButton {
        private String text;
        private int imageResId;
        private int color;
        private int pos;
        private RectF clickRegion;
        private UnderlayButtonClickListener clickListener;

        public UnderlayButton(String text, int imageResId, int color, UnderlayButtonClickListener clickListener) {
            this.text = text;
            this.imageResId = imageResId;
            this.color = color;
            this.clickListener = clickListener;
        }

        public boolean onClick(float x, float y){
            if (clickRegion != null && clickRegion.contains(x, y)){
                clickListener.onClick(pos);
                return true;
            }

            return false;
        }

        public void onDraw(Canvas c, RectF rect, int pos){
            Paint p = new Paint();

            // Draw background
            p.setColor(color);
            c.drawRect(rect, p);

            // Draw Text
            p.setColor(Color.WHITE);
            p.setTextSize(LayoutHelper.getPx(MyApplication.getAppContext(), 12));

            Rect r = new Rect();
            float cHeight = rect.height();
            float cWidth = rect.width();
            p.setTextAlign(Paint.Align.LEFT);
            p.getTextBounds(text, 0, text.length(), r);
            float x = cWidth / 2f - r.width() / 2f - r.left;
            float y = cHeight / 2f + r.height() / 2f - r.bottom;
            c.drawText(text, rect.left + x, rect.top + y, p);

            clickRegion = rect;
            this.pos = pos;
        }
    }

    public interface UnderlayButtonClickListener {
        void onClick(int pos);
    }
}

用法:

SwipeHelper swipeHelper = new SwipeHelper(this, recyclerView) {
    @Override
    public void instantiateUnderlayButton(RecyclerView.ViewHolder viewHolder, List<UnderlayButton> underlayButtons) {
        underlayButtons.add(new SwipeHelper.UnderlayButton(
                "Delete",
                0,
                Color.parseColor("#FF3C30"),
                new SwipeHelper.UnderlayButtonClickListener() {
                    @Override
                    public void onClick(int pos) {
                        // TODO: onDelete
                    }
                }
        ));

        underlayButtons.add(new SwipeHelper.UnderlayButton(
                "Transfer",
                0,
                Color.parseColor("#FF9502"),
                new SwipeHelper.UnderlayButtonClickListener() {
                    @Override
                    public void onClick(int pos) {
                        // TODO: OnTransfer
                    }
                }
        ));
        underlayButtons.add(new SwipeHelper.UnderlayButton(
                "Unshare",
                0,
                Color.parseColor("#C7C7CB"),
                new SwipeHelper.UnderlayButtonClickListener() {
                    @Override
                    public void onClick(int pos) {
                        // TODO: OnUnshare
                    }
                }
        ));
    }
};

注意:这个帮助类是为左滑设计的。您可以在 SwipeHelper 的 构造函数中更改滑动方向，并在 onChildDraw 方法中根据 dX 进行相应的更改。

如果要在按钮中显示图片，只需在UnderlayButton中使用imageResId，并重新实现onDraw方法.

有一个已知的错误，当你从一个项目对角滑动一个项目到另一个项目时，第一个触摸的项目会闪烁一点。这可以通过减小 getSwipeVelocityThreshold 的值来解决，但这会使用户更难滑动项目。您还可以通过更改 getSwipeThreshold 和 getSwipeEscapeVelocity 中的另外两个值来调整滑动感觉。查看 ItemTouchHelper 源码，评论很有帮助。

我相信有很多地方可以优化。如果您想坚持使用 ItemTouchHelper，此解决方案只是给出了一个想法。如果您在使用它时遇到问题，请告诉我。下面是一个截图。

致谢:这个解决方案的灵感主要来自 AdamWei 在 post 中的回答

关于android - 滑动时的 RecyclerView ItemTouchHelper 按钮，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/44965278/