Android的RecyclerView拖放功能
在这个教程中，我们将讨论并在Android应用程序中实现RecyclerView的拖放功能。我们已经在之前的教程中讨论过滑动删除功能。
RecyclerView 拖拽和放置
可以使用ItemTouchHelper实用类将“拖放”功能添加到RecyclerView中。以下是ItemTouchHelper.Callback接口中需要实现的重要方法：
- isLongPressDragEnabled – return true here to enable long press on the RecyclerView rows for drag and drop.
- isItemViewSwipeEnabled – This is used to enable or disable swipes. In this tutorial, we’ll disable this.
- getMovementFlags – Here we pass the flags for the directions of drag and swipe. Since swipe is disable we pass 0 for it.
- onMove – Here we set the code for the drag and drop. onSwipe – Here we implement the code for swiping. We’ll keep this empty in the current tutorial.
- onSelectedChanged – Based on the current state of the RecyclerView and whether it’s pressed or swiped, this method gets triggered. Here we can customize the RecyclerView row. For example, changing the background color.
- clearView – This method gets triggered when the user interaction stops with the RecyclerView row.
让我们使用RecyclerView的拖放功能开始构建我们的安卓应用程序。
项目结构
編碼
以下是包含一个 RecyclerView 的 activity_main.xml 布局的代码：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:layout_height="match_parent"
tools:context=".MainActivity">
<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" />
</LinearLayout>
下面是MainActivity.java的代码：
package com.Olivia.androidrecyclerviewdraganddrop;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.helper.ItemTouchHelper;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
RecyclerView recyclerView;
RecyclerViewAdapter mAdapter;
ArrayList<String> stringArrayList = new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = findViewById(R.id.recyclerView);
populateRecyclerView();
}
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);
ItemTouchHelper.Callback callback =
new ItemMoveCallback(mAdapter);
ItemTouchHelper touchHelper = new ItemTouchHelper(callback);
touchHelper.attachToRecyclerView(recyclerView);
recyclerView.setAdapter(mAdapter);
}
}
在这里，我们用一个字符串的ArrayList填充了一个RecyclerViewAdapter.java类。我们在RecyclerView上附加了一个ItemMoveCallback.java类的实例，以启动拖放操作。让我们看看这些文件的每一个。ItemMoveCallback.java类的代码如下：
package com.Olivia.androidrecyclerviewdraganddrop;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.helper.ItemTouchHelper;
public class ItemMoveCallback extends ItemTouchHelper.Callback {
private final ItemTouchHelperContract mAdapter;
public ItemMoveCallback(ItemTouchHelperContract adapter) {
mAdapter = adapter;
}
@Override
public boolean isLongPressDragEnabled() {
return true;
}
@Override
public boolean isItemViewSwipeEnabled() {
return false;
}
@Override
public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int i) {
}
@Override
public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
return makeMovementFlags(dragFlags, 0);
}
@Override
public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder,
RecyclerView.ViewHolder target) {
mAdapter.onRowMoved(viewHolder.getAdapterPosition(), target.getAdapterPosition());
return true;
}
@Override
public void onSelectedChanged(RecyclerView.ViewHolder viewHolder,
int actionState) {
if (actionState != ItemTouchHelper.ACTION_STATE_IDLE) {
if (viewHolder instanceof RecyclerViewAdapter.MyViewHolder) {
RecyclerViewAdapter.MyViewHolder myViewHolder=
(RecyclerViewAdapter.MyViewHolder) viewHolder;
mAdapter.onRowSelected(myViewHolder);
}
}
super.onSelectedChanged(viewHolder, actionState);
}
@Override
public void clearView(RecyclerView recyclerView,
RecyclerView.ViewHolder viewHolder) {
super.clearView(recyclerView, viewHolder);
if (viewHolder instanceof RecyclerViewAdapter.MyViewHolder) {
RecyclerViewAdapter.MyViewHolder myViewHolder=
(RecyclerViewAdapter.MyViewHolder) viewHolder;
mAdapter.onRowClear(myViewHolder);
}
}
public interface ItemTouchHelperContract {
void onRowMoved(int fromPosition, int toPosition);
void onRowSelected(RecyclerViewAdapter.MyViewHolder myViewHolder);
void onRowClear(RecyclerViewAdapter.MyViewHolder myViewHolder);
}
}
在这里，我们定义了一个接口ItemTouchHelperContract。它的每个方法都会从ItemTouchHelper.Callback接口的实现方法中被调用。RecyclerViewAdapter.java类的代码如下：
package com.Olivia.androidrecyclerviewdraganddrop;
import android.graphics.Color;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.Collections;
public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.MyViewHolder> implements ItemMoveCallback.ItemTouchHelperContract {
private ArrayList<String> data;
public class MyViewHolder extends RecyclerView.ViewHolder {
private TextView mTitle;
View rowView;
public MyViewHolder(View itemView) {
super(itemView);
rowView = 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();
}
@Override
public void onRowMoved(int fromPosition, int toPosition) {
if (fromPosition < toPosition) {
for (int i = fromPosition; i < toPosition; i++) {
Collections.swap(data, i, i + 1);
}
} else {
for (int i = fromPosition; i > toPosition; i--) {
Collections.swap(data, i, i - 1);
}
}
notifyItemMoved(fromPosition, toPosition);
}
@Override
public void onRowSelected(MyViewHolder myViewHolder) {
myViewHolder.rowView.setBackgroundColor(Color.GRAY);
}
@Override
public void onRowClear(MyViewHolder myViewHolder) {
myViewHolder.rowView.setBackgroundColor(Color.WHITE);
}
}
当拖拽和放下操作完成时，之前在Contract接口中定义的onRowMoved会被调用。在这里，我们交换数组列表中两个行的位置，并调用notifyItemMoved来刷新适配器。上述应用程序的输出如下所示：到目前为止，我们通过在RecyclerView的行中的任意位置按下来进行拖拽和放下操作。接下来，我们将看到如何仅通过按下RecyclerView行内的特定视图来执行相同的操作。
使用手柄进行拖放
为了使用特定的句柄视图进行拖放操作，我们需要按照以下步骤进行：将isLongPressDragEnabled设置为false，以禁用默认的拖放功能。创建一个类似的接口：
public interface StartDragListener {
void requestDrag(RecyclerView.ViewHolder viewHolder);
}
将其实施于MainActivity并将其传递给适配器。
@Override
public void requestDrag(RecyclerView.ViewHolder viewHolder) {
touchHelper.startDrag(viewHolder);
}
mAdapter = new RecyclerViewAdapter(stringArrayList,this);
在RecyclerViewAdapter.java文件中进行以下操作：
holder.imageView.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
if (event.getAction() ==
MotionEvent.ACTION_DOWN) {
mStartDragListener.requestDrag(holder);
}
return false;
}
});
你可以在教程末尾的下载链接中找到更新后的代码。使用更新后的代码，应用的输出如下所示：教程到此结束。项目的完整源代码如下所示：
安卓的RecyclerView拖放功能。
GitHub 项目链接