一、ItemTouchHelper是什么
官方解釋：This is a utility class to add swipe to dismiss and drag & drop support to RecyclerView.
這是一個(gè)支持RecyclerView滑動刪除和拖拽的實(shí)用工具類
二永丝、如何使用
ItemTouchHelper itemTouchHelper = new ItemTouchHelper(mCallback);
itemTouchHelper.attachToRecyclerView(mRecyclerView);
就這么兩行眯勾，就可以使用了晨川，不過我們也看見了在創(chuàng)建ItemTouchHelper 對象時(shí)连舍，需要傳入一個(gè)Callback對象，這就是關(guān)鍵之處了.
三小腊、ItemTouchHelper.Callback
ItemTouchHelper.Callback定義在ItemTouchHelper中揍庄，是一個(gè)抽象類咆蒿，它還有一個(gè)子類SimpleCallback，也是抽象類.
如果只想要一個(gè)基本的實(shí)現(xiàn),繼承SimpleCallback實(shí)現(xiàn)對應(yīng)的方法即可蚂子，這里我們?yōu)榱肆私馄涔ぷ鳈C(jī)制沃测，先來看一看ItemTouchHelper.Callback的常用方法
1）基本的拖動排序與滑動刪除需要重寫的方法
/**
* 指定可以拖拽（drag）和滑動（swipe）的方向
* ItemTouchHelper.UP、ItemTouchHelper.DOWN
* ItemTouchHelper.LEFT食茎、ItemTouchHelper.RIGHT
* ItemTouchHelper.START蒂破、ItemTouchHelper.END
* 若返回0，表示不觸發(fā)滑動or拖拽
*/
@Override
public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
return 0;
}
/**
* 拖拽到新位置時(shí)候的回調(diào)方法
* @param viewHolder 拖動的ViewHolder
* @param target 目標(biāo)位置的ViewHolder
*/
@Override
public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
return false;
}
/**
* 滑動時(shí)的回調(diào)方法
* @param viewHolder 滑動的ViewHolder
* @param direction 滑動的方向
*/
@Override
public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
}
2）兩個(gè)支持方法
/**
* 是否支持長按拖拽别渔，默認(rèn)為true附迷，表示支持長按拖拽
* 對應(yīng)長按移動位置功能
* 也可以返回false，手動調(diào)用startDrag()方法啟動拖拽
*/
@Override
public boolean isLongPressDragEnabled() {
return super.isLongPressDragEnabled();
}
/**
* 是否支持任意位置觸摸事件發(fā)生時(shí)啟用滑動操作哎媚，默認(rèn)為true喇伯，表示支持滑動
* 對應(yīng)滑動刪除功能
* 也可以返回false，手動調(diào)用startSwipe()方法啟動滑動
*/
@Override
public boolean isItemViewSwipeEnabled() {
return super.isItemViewSwipeEnabled();
}
四拨与、實(shí)現(xiàn)我們自己的回調(diào)
ItemTouchHelper.SimpleCallback mCallback =
new ItemTouchHelper.SimpleCallback(ItemTouchHelper.UP |
ItemTouchHelper.DOWN | ItemTouchHelper.LEFT |ItemTouchHelper.RIGHT,
ItemTouchHelper.START | ItemTouchHelper.END) {
@Override
public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
int fromPosition = viewHolder.getAdapterPosition();//得到拖動ViewHolder的position
int toPosition = target.getAdapterPosition();//得到目標(biāo)ViewHolder的position
//使用集合工具類Collections稻据，分別把中間所有的item的位置重新交換
if (fromPosition < toPosition) {
for (int i = fromPosition; i < toPosition; i++) {
Collections.swap(mDatas, i, i + 1);
}
} else {
for (int i = fromPosition; i > toPosition; i--) {
Collections.swap(mDatas, i, i - 1);
}
}
//通知Adapter更新狀態(tài)
mAdapter.notifyItemMoved(fromPosition, toPosition);
return true;
}
@Override
public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
int position = viewHolder.getAdapterPosition();
mDatas.remove(position);//側(cè)滑刪除數(shù)據(jù)
mAdapter.notifyItemRemoved(position); //通知Adapter更新狀態(tài)
}
@Override
public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
if (actionState == ItemTouchHelper.ACTION_STATE_SWIPE) {
//滑動時(shí)改變Item的透明度
final float alpha = 1 - Math.abs(dX) / (float) viewHolder.itemView.getWidth();
viewHolder.itemView.setAlpha(alpha);
viewHolder.itemView.setTranslationX(dX);
}
}
};
繼承SimpleCallback ，必須要實(shí)現(xiàn)onMove（）买喧、onSwiped（）方法捻悯，同時(shí)在構(gòu)造方法里面需要把拖拽（drag）和滑動（swipe）的方向傳遞過來（代替了getMovementFlags方法）.
五匆赃、所有代碼
1、布局文件
MainActivity的：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerview"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
item的：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#ff33b5e5">
<TextView
android:id="@+id/tv"
android:layout_width="match_parent"
android:layout_height="40dp"
android:gravity="center"
tools:text="別看了今缚，我就是一個(gè)TextView" />
</RelativeLayout>
2算柳、MainActivity.java
public class MainActivity extends AppCompatActivity {
private RecyclerView mRecyclerView;
private MainAdapter mAdapter;
private List<String> mDatas;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initData();
mRecyclerView = (RecyclerView) findViewById(R.id.recyclerview);
mRecyclerView.setLayoutManager(new LinearLayoutManager(this,LinearLayoutManager.VERTICAL,false));
mRecyclerView.addItemDecoration(new DividerItemDecoration(this,DividerItemDecoration.VERTICAL));
mAdapter = new MainAdapter(this,mDatas);
mRecyclerView.setAdapter(mAdapter);
ItemTouchHelper.SimpleCallback mCallback = new ItemTouchHelper.SimpleCallback(ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT,
ItemTouchHelper.START | ItemTouchHelper.END) {
@Override
public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
int fromPosition = viewHolder.getAdapterPosition();
int toPosition = target.getAdapterPosition();
if (fromPosition < toPosition) {
for (int i = fromPosition; i < toPosition; i++) {
Collections.swap(mDatas, i, i + 1);
}
} else {
for (int i = fromPosition; i > toPosition; i--) {
Collections.swap(mDatas, i, i - 1);
}
}
mAdapter.notifyItemMoved(fromPosition, toPosition);
return true;
}
@Override
public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
int position = viewHolder.getAdapterPosition();
mDatas.remove(position);
mAdapter.notifyItemRemoved(position);
}
@Override
public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder,
float dX, float dY, int actionState, boolean isCurrentlyActive) {
super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
if (actionState == ItemTouchHelper.ACTION_STATE_SWIPE) {
final float alpha = 1 - Math.abs(dX) / (float) viewHolder.itemView.getWidth();
viewHolder.itemView.setAlpha(alpha);
viewHolder.itemView.setTranslationX(dX);
}
}
};
ItemTouchHelper itemTouchHelper = new ItemTouchHelper(mCallback);
itemTouchHelper.attachToRecyclerView(mRecyclerView);
}
private void initData() {
mDatas = new ArrayList<>();
for (int i = 'A'; i < 'Z'; i++) {
mDatas.add("" + (char) i);
}
}
}
3、Adapter中
public class MainAdapter extends RecyclerView.Adapter<MainAdapter.MyViewHolder> {
private Context mContext;
private List<String> mDatas;
public MainAdapter(Context context, List<String> mDatas) {
this.mContext = context;
this.mDatas = mDatas;
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = View.inflate(mContext, R.layout.item_layout, null);
return new MyViewHolder(view);
}
@Override
public void onBindViewHolder(MyViewHolder holder, final int position) {
holder.tv.setText(mDatas.get(position));
}
@Override
public int getItemCount() {
return mDatas.size();
}
class MyViewHolder extends RecyclerView.ViewHolder {
TextView tv;
public MyViewHolder(View view) {
super(view);
tv = (TextView)itemView.findViewById(R.id.tv);
}
}
}
六荚斯、效果圖及總結(jié)
ItemTouchHelper不僅僅支持LinearLayoutManager埠居，對于GridLayoutManager和StaggeredGridLayoutManager也都是支持的，像新聞app中常見的拖動標(biāo)簽效果事期，利用ItemTouchHelper可以很輕松的實(shí)現(xiàn).
