ItemTouchHelper类及RecyclerView的item滑动删除和拖拽案例

ItemTouchHelper类是v7包下的一个针对RecyclerView拖拽和滑动删除的辅助类，英文的解释：This is a utility class to add swipe to dismiss and drag & drop support to RecyclerView.

下面用一个例子介绍一下：

先看效果图：



先介绍一下项目的结构图：



简要说明

helper文件夹中，是自己定义的接口和类，ItemTouchHelperAdapter和ItemTouchHelperViewHolder是需要RecyclerView.Adapter和RecyclerView.ViewHolder的子类去实现的。SimpleItemTouchHelperCallback继承了ItemTouchHelper.Callback，在SimpleItemTouchHelperCallback需要实现3个方法，分别是getMovementFlags()，onMove()，onSwiped()。

ItemTouchHelper.Callback中的几个方法

getMovementFlags()：应该返回一个组合标志，它定义了在每个状态下启用的移动方向

原文解释：Should return a composite flag which defines the enabled move directions in each state(idle, swiping, dragging).

onMove():当把之前的位置拖拽到新的位置上时调用

原文解释： Called when ItemTouchHelper wants to move the dragged item from its old position to the new position.

onSwiped():当ViewHolder被用户滑动删除后调用。

原文解释：Called when a ViewHolder is swiped by the user.

-onChildDraw():在RecyclerView调用onDraw方法的时候，调用此方法

原文解释：Called by ItemTouchHelper on RecyclerView’s onDraw callback

可以在这个方法中，对itemView进行设置。如透明度，背景的变化等

onSelectedChanged（）：当item’touViewHolder拖拽或滑动

原文解释：Called when the ViewHolder swiped or dragged by the ItemTouchHelper is changed.

clearView（）：当用户与itemview交互完且动画执行完，调用

原文解释：Called by the ItemTouchHelper when the user interaction with an element is over and it also completed its animation.

将RecyclerView依附到ItemTouchHelper中

ItemTouchHelper.Callback callback = new SimpleItemTouchHelperCallback(adapter);
itemTouchHelper = new ItemTouchHelper(callback);
itemTouchHelper.attachToRecyclerView(mRecyclerView);

下面看具体代码：

helper文件夹中：

ItemTouchHelperAdapter接口

public interface ItemTouchHelperAdapter {
void onItemMove(int fromPosition , int toPosition);
void onItemDelete(int position);
}

ItemTouchHelperViewHolder接口

public interface ItemTouchHelperViewHolder {
void onItemSelect();
void onItemClear();
}

SimpleItemTouchHelperCallback

public class SimpleItemTouchHelperCallback extends ItemTouchHelper.Callback {

private static final float ALPHA_NORMAL = 1.0f;
private ItemTouchHelperAdapter mAdapter;

public SimpleItemTouchHelperCallback(ItemTouchHelperAdapter adapter) {
this.mAdapter = adapter;
}

@Override
public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {

if (recyclerView.getLayoutManager() instanceof GridLayoutManager) {
int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.START | ItemTouchHelper.END;
int swipeFlags = 0;
return makeMovementFlags(dragFlags, swipeFlags);
} else if (recyclerView.getLayoutManager() instanceof LinearLayoutManager) {
int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
int swipeFlags = ItemTouchHelper.START | ItemTouchHelper.END;
return makeMovementFlags(dragFlags, swipeFlags);
}
return 0;
}

@Override
public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {

if (viewHolder.getItemViewType() != target.getItemViewType()) {
return false;
}

mAdapter.onItemMove(viewHolder.getAdapterPosition(), target.getAdapterPosition());

return true;
}

@Override
public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
mAdapter.onItemDelete(viewHolder.getAdapterPosition());
}

@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) {
float alpha = ALPHA_NORMAL - Math.abs(dX) / viewHolder.itemView.getWidth();
viewHolder.itemView.setAlpha(alpha);
viewHolder.itemView.setTranslationX(dX);
} else {
super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
}

}

@Override
public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {

if (actionState != ItemTouchHelper.ACTION_STATE_IDLE) {
if (viewHolder instanceof ItemTouchHelperViewHolder) {
ItemTouchHelperViewHolder itemTouchHelperViewHolder = (ItemTouchHelperViewHolder) viewHolder;
itemTouchHelperViewHolder.onItemSelect();
}
}

super.onSelectedChanged(viewHolder, actionState);
}

@Override
public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
super.clearView(recyclerView, viewHolder);

viewHolder.itemView.setAlpha(ALPHA_NORMAL);

if (viewHolder instanceof ItemTouchHelperViewHolder) {
ItemTouchHelperViewHolder itemTouchHelperViewHolder = (ItemTouchHelperViewHolder) viewHolder;
itemTouchHelperViewHolder.onItemClear();
}
}
}

布局文件：

activity.xml

<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="match_parent"
tools:context="www.weshared.myitemtouchhelper.MainActivity">

<FrameLayout
android:id="@+id/fragment_list"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/white"
android:visibility="visible" />

<FrameLayout
android:id="@+id/fragment_grid"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/white"
android:visibility="gone" />

<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_marginBottom="20dp"
android:layout_marginRight="20dp"
android:src="@mipmap/list" />

</RelativeLayout>

fragment.xml文件

<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="match_parent"
tools:context="www.weshared.myitemtouchhelper.MainActivity">

<android.support.v7.widget.RecyclerView
android:id="@+id/recycler"
android:layout_width="match_parent"
android:layout_height="wrap_content" />

</RelativeLayout>

recycler_item文件：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">

<TextView
android:id="@+id/recycler_tv"
android:textColor="@android:color/black"
android:gravity="center"
android:textSize="16sp"
android:layout_width="match_parent"
android:layout_height="60dp" />

</LinearLayout>

在MainActivity文件中：

public class MainActivity extends AppCompatActivity {

private FloatingActionButton fab;
private boolean isList = true;
private FragmentTransaction fragmentTransaction_list;
private FragmentTransaction fragmentTransaction_grid;
private ListFragment listFragment;
private GridFragment gridFragment;
private FrameLayout frameLayout_grid;
private FrameLayout frameLayout_list;

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

initView();
initListener();
}

private void initView() {
fab = (FloatingActionButton) findViewById(R.id.fab);
frameLayout_list = (FrameLayout) findViewById(R.id.fragment_list);
frameLayout_grid = (FrameLayout) findViewById(R.id.fragment_grid);
listFragment = new ListFragment();
gridFragment = new GridFragment();
fragmentTransaction_list = getSupportFragmentManager().beginTransaction().replace(R.id.fragment_list, listFragment, "list");
fragmentTransaction_list.commit();
fragmentTransaction_grid = getSupportFragmentManager().beginTransaction().replace(R.id.fragment_grid, gridFragment, "grid");
fragmentTransaction_grid.commit();
}

private void initListener() {
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (isList) {
frameLayout_list.setVisibility(View.GONE);
frameLayout_grid.setVisibility(View.VISIBLE);
fab.setImageResource(R.mipmap.grid);
isList = false;
} else {
frameLayout_list.setVisibility(View.VISIBLE);
frameLayout_grid.setVisibility(View.GONE);
fab.setImageResource(R.mipmap.list);
isList = true;
}
}
});
}
}

ListFragment文件

public class ListFragment extends Fragment {

private RecyclerView mRecyclerView;
private RecyclerView.LayoutManager manager;
private MyAdapter adapter;
private ItemTouchHelper itemTouchHelper;
private List<String> mdatas = new ArrayList<>();

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

View view = inflater.inflate(R.layout.fragment, container, false);
return view;
}

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
mRecyclerView = (RecyclerView) view.findViewById(R.id.recycler);
manager = new LinearLayoutManager(getContext(), LinearLayoutManager.VERTICAL, false);
initData();
initRecycler();
}

private void initData() {
for (int i = 0; i < 30; i++) {
mdatas.add("这是第" + i + "item");
}
}

private void initRecycler() {

mRecyclerView.setLayoutManager(manager);
mRecyclerView.setHasFixedSize(true);
adapter = new MyAdapter(getContext(), mdatas);
mRecyclerView.setAdapter(adapter);

//RecyclerView与ItemTouchHelper关联
ItemTouchHelper.Callback callback = new SimpleItemTouchHelperCallback(adapter);
itemTouchHelper = new ItemTouchHelper(callback);
itemTouchHelper.attachToRecyclerView(mRecyclerView);
}
}

GridFragment 文件与ListFragment基本相同，不相同的只有LayoutManager.

//初始化的时候换成GridLayoutManager对象
manager = new GridLayoutManager(getContext(),2);

MyAdapter文件

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> implements ItemTouchHelperAdapter {

private Context mContext;
private List<String> mDatas = new ArrayList<>();

public MyAdapter(Context context, List<String> mdatas) {
this.mContext = context;
this.mDatas = mdatas;
}

@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

View view = LayoutInflater.from(mContext).inflate(R.layout.recycler_item, parent, false);

return new MyViewHolder(view);
}

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

@Override
public int getItemCount() {
if (null == mDatas) {
return 0;
}
return mDatas.size();
}

@Override
public void onItemMove(int fromPosition, int toPosition) {
Collections.swap(mDatas, fromPosition, toPosition);
notifyItemMoved(fromPosition, toPosition);
}

@Override
public void onItemDelete(int position) {
mDatas.remove(position);
notifyItemRemoved(position);
}

class MyViewHolder extends RecyclerView.ViewHolder implements ItemTouchHelperViewHolder {

TextView textView;

public MyViewHolder(View itemView) {
super(itemView);
initView();
initListener();
}

private void initView() {
textView = (TextView) itemView.findViewById(R.id.recycler_tv);
}

private void initListener() {
//事件监听
}

@Override
public void onItemSelect() {
itemView.setBackgroundColor(Color.LTGRAY);
}

@Override
public void onItemClear() {
itemView.setBackgroundColor(0);
}
}
}