安卓开发：RecyclerView滑动删除和撤销功能详解

2 年 ago

新, 韵

6 minutes

在这个教程中，我们将讨论并在我们的Android应用程序中实现在RecyclerView上的滑动删除功能。

安卓滑动删除滑动删除功能通常用于从RecyclerView中删除行。为了实现滑动删除功能，我们需要使用ItemTouchHelper实用类。

ItemTouchHelper.Callback (ItemTouchHelper回调)为了使用ItemTouchHelper类，我们需要实现ItemTouchHelper.Callback。ItemTouchHelper.Callback类主要用于拖放和滑动删除行为。在本教程中，我们将只使用滑动删除。Android框架为我们提供了ItemTouchHelper.Callback的基本实现，即SimpleCallback。我们将创建我们自己的滑动删除功能实现。以下是需要在我们的类中重写的主要方法：getMovementFlags-在这里我们设置滑动的方向。我们在一个静态方法makeMovementFlags中返回方向标志。onMove-这用于拖放。如果不需要，请在此处返回false。onSwiped-当检测到滑动操作时会触发此方法。完整的滑动会覆盖整个屏幕宽度。为了将部分滑动视为滑动，我们需要重写以下方法：getSwipeThreshold-在这里我们返回浮点值。例如，0.5f表示RecyclerView行的50％滑动将被视为滑动。onChildDraw-在这里，我们将创建自定义视图，显示出滑动正在进行。

ItemTouchHelper.Callback 用于只滑动行。它本身并没有删除行的功能。我们需要使用 RecyclerView Adapter 自己将其删除。

够说了，开始编码吧。在接下来的部分，我们将使用RecyclerView创建我们的Android应用程序，并添加滑动删除功能。我们还将提供一个Snackbar来提供撤销选项。

项目结构在应用的 build.gradle 文件中添加以下依赖项。

implementation 'com.android.support:design:28.0.0-rc01'

代码下面是activity_main.xml布局的代码。

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="https://schemas.android.com/apk/res/android"
    xmlns:app="https://schemas.android.com/apk/res-auto"
    xmlns:tools="https://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:id="@+id/coordinatorLayout"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layoutManager="android.support.v7.widget.LinearLayoutManager" />


    </RelativeLayout>

</android.support.design.widget.CoordinatorLayout>

以下是扩展ItemTouchHelper.Callback类的SwipeToDeleteCallback.java类的代码：

package com.Olivia.androidrecyclerviewswipetodelete;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.drawable.ColorDrawable;
import android.graphics.drawable.Drawable;
import android.support.annotation.NonNull;
import android.support.v4.content.ContextCompat;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.helper.ItemTouchHelper;
import android.view.View;

abstract public class SwipeToDeleteCallback extends ItemTouchHelper.Callback {

    Context mContext;
    private Paint mClearPaint;
    private ColorDrawable mBackground;
    private int backgroundColor;
    private Drawable deleteDrawable;
    private int intrinsicWidth;
    private int intrinsicHeight;


    SwipeToDeleteCallback(Context context) {
        mContext = context;
        mBackground = new ColorDrawable();
        backgroundColor = Color.parseColor("#b80f0a");
        mClearPaint = new Paint();
        mClearPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
        deleteDrawable = ContextCompat.getDrawable(mContext, R.drawable.ic_delete);
        intrinsicWidth = deleteDrawable.getIntrinsicWidth();
        intrinsicHeight = deleteDrawable.getIntrinsicHeight();
        

    }


    @Override
    public int getMovementFlags(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {
        return makeMovementFlags(0, ItemTouchHelper.LEFT);
    }

    @Override
    public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder viewHolder1) {
        return false;
    }

    @Override
    public void onChildDraw(@NonNull Canvas c, @NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
        super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);

        View itemView = viewHolder.itemView;
        int itemHeight = itemView.getHeight();

        boolean isCancelled = dX == 0 && !isCurrentlyActive;

        if (isCancelled) {
            clearCanvas(c, itemView.getRight() + dX, (float) itemView.getTop(), (float) itemView.getRight(), (float) itemView.getBottom());
            super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
            return;
        }

        mBackground.setColor(backgroundColor);
        mBackground.setBounds(itemView.getRight() + (int) dX, itemView.getTop(), itemView.getRight(), itemView.getBottom());
        mBackground.draw(c);

        int deleteIconTop = itemView.getTop() + (itemHeight - intrinsicHeight) / 2;
        int deleteIconMargin = (itemHeight - intrinsicHeight) / 2;
        int deleteIconLeft = itemView.getRight() - deleteIconMargin - intrinsicWidth;
        int deleteIconRight = itemView.getRight() - deleteIconMargin;
        int deleteIconBottom = deleteIconTop + intrinsicHeight;


        deleteDrawable.setBounds(deleteIconLeft, deleteIconTop, deleteIconRight, deleteIconBottom);
        deleteDrawable.draw(c);

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


    }

    private void clearCanvas(Canvas c, Float left, Float top, Float right, Float bottom) {
        c.drawRect(left, top, right, bottom, mClearPaint);

    }

    @Override
    public float getSwipeThreshold(@NonNull RecyclerView.ViewHolder viewHolder) {
        return 0.7f;
    }
}

由于我们尚未实现onSwipe方法，该类是抽象的。我们将在MainActivity.java类中完成这个方法。在onChildDraw方法中，我们使用isCancelled布尔值来检查是否进行了滑动操作。基于这一点，我们创建一个带有删除图标的视图。我们将Swipe阈值设置为0.7，这意味着如果行被划动的比例少于70％，onSwipe方法不会被触发。以下是MainActivity.java类的代码。

package com.Olivia.androidrecyclerviewswipetodelete;

import android.graphics.Color;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.CoordinatorLayout;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.helper.ItemTouchHelper;
import android.view.View;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {


    RecyclerView recyclerView;
    RecyclerViewAdapter mAdapter;
    ArrayList<String> stringArrayList = new ArrayList<>();
    CoordinatorLayout coordinatorLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        recyclerView = findViewById(R.id.recyclerView);
        coordinatorLayout = findViewById(R.id.coordinatorLayout);

        populateRecyclerView();
        enableSwipeToDeleteAndUndo();


    }

    private void populateRecyclerView() {
        stringArrayList.add("Item 1");
        stringArrayList.add("Item 2");
        stringArrayList.add("Item 3");
        stringArrayList.add("Item 4");
        stringArrayList.add("Item 5");
        stringArrayList.add("Item 6");
        stringArrayList.add("Item 7");
        stringArrayList.add("Item 8");
        stringArrayList.add("Item 9");
        stringArrayList.add("Item 10");

        mAdapter = new RecyclerViewAdapter(stringArrayList);
        recyclerView.setAdapter(mAdapter);


    }

    private void enableSwipeToDeleteAndUndo() {
        SwipeToDeleteCallback swipeToDeleteCallback = new SwipeToDeleteCallback(this) {
            @Override
            public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int i) {

                
                final int position = viewHolder.getAdapterPosition();
                final String item = mAdapter.getData().get(position);

                mAdapter.removeItem(position);


                Snackbar snackbar = Snackbar
                        .make(coordinatorLayout, "Item was removed from the list.", Snackbar.LENGTH_LONG);
                snackbar.setAction("UNDO", new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        
                        mAdapter.restoreItem(item, position);
                        recyclerView.scrollToPosition(position);
                    }
                });

                snackbar.setActionTextColor(Color.YELLOW);
                snackbar.show();

            }
        };

        ItemTouchHelper itemTouchhelper = new ItemTouchHelper(swipeToDeleteCallback);
        itemTouchhelper.attachToRecyclerView(recyclerView);
    }


}

为了将ItemTouchHelper设置到RecyclerView上，使用attachToRecyclerView方法。当点击Snackbar动作时，我们使用restoreItem方法将项目恢复到RecyclerView中。restoreItem方法在RecyclerViewAdapter类中定义。scrollToPosition将RecyclerView滚动到指定位置。当在RecyclerView顶部插入一个项目时，主要使用这个方法。cardview_row.xml的代码如下：

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="https://schemas.android.com/apk/res/android"
    xmlns:card_view="https://schemas.android.com/apk/res-auto"
    android:id="@+id/cardView"
    android:layout_width="match_parent"
    android:layout_height="64dp"
    android:layout_margin="8dp"
    card_view:cardCornerRadius="0dp"
    card_view:cardElevation="2dp">


    <RelativeLayout
        android:id="@+id/relativeLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingBottom="8dp"
        android:paddingLeft="8dp"
        android:paddingRight="8dp">


        <TextView
            android:id="@+id/txtTitle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerVertical="true"
            android:text="Item 1"
            android:textAppearance="@style/TextAppearance.Compat.Notification.Title" />
    </RelativeLayout>

</android.support.v7.widget.CardView>

以下是RecyclerViewAdapter.java类的代码：

package com.Olivia.androidrecyclerviewswipetodelete;

import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.RelativeLayout;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.MyViewHolder> {

    private ArrayList<String> data;

    public class MyViewHolder extends RecyclerView.ViewHolder {

        private TextView mTitle;
        RelativeLayout relativeLayout;

        public MyViewHolder(View itemView) {
            super(itemView);

            mTitle = itemView.findViewById(R.id.txtTitle);
        }
    }

    public RecyclerViewAdapter(ArrayList<String> data) {
        this.data = data;
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.cardview_row, parent, false);
        return new MyViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        holder.mTitle.setText(data.get(position));
    }

    @Override
    public int getItemCount() {
        return data.size();
    }


    public void removeItem(int position) {
        data.remove(position);
        notifyItemRemoved(position);
    }

    public void restoreItem(String item, int position) {
        data.add(position, item);
        notifyItemInserted(position);
    }

    public ArrayList<String> getData() {
        return data;
    }
}

以下是该应用程序的输出结果：本教程到此结束。您可以从以下链接下载该项目。

AndroidRecyclerViewSwipeToDelete 删除

Github 项目链接

#Android开发 #Material Design #RecyclerView #撤销功能 #滑动删除