标签：adapter 手势 public 重写 解析 pad lin log tle
ItemTouchHelper在RecyclerView的整个体系中，负责监听Item的手势操作，我们通过给它设置一个继承于ItemTouchHelper.Callback的子类，在其中处理Item的UI变化，就可以完成侧滑删除、拖动排序等操作，下面，我们分以下几部介绍：
API解析API分析对于Item的手势操作分为两种：侧滑和拖动，如果需要支持这两种，那么需要给ItemTouchHelper传入一个ItemTouchHelper.Callback的子类，并把ItemTouchHelper和RecyclerView关联起来，下面，我们先来介绍一下ItemTouchHelper.Callback个回调方法的含义：
public boolean isLongPressDragEnabled()true，如果返回false，那么可以通过startDrag(ViewHolder)方法来触发某个特定Item的拖动的机制。public boolean isItemViewSwipeEnabled()Item进行侧滑。public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder)ViewHolder可以移动的方向，可选的值有UP/DOWN/LEFT/RIGHT/START/END。对于纵向排列的线性布局而言，如果要支持上下拖动排序，那么就要标志位中就要包含UP&DOWN，而如果需要支持左滑删除，那么标志位中就要包含LEFT。public abstract boolean onMove(RecyclerView recyclerView, ViewHolder viewHolder, ViewHolder target)Item被从旧位置拖动到了新位置后回调，如果返回true，那么ItemTouchHelper就认为viewHolder已经被移动到了target在Adapter中的位置。public abstract void onSwiped(ViewHolder viewHolder, int direction)Item被滑动到消失时回调，direction表示滑动的方向。public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState)Item的状态发生改变时，回调该方法，actionState的取值有ACTION_STATE_IDLE/ACTION_STATE_SWIPE/ACTION_STATE_DRAG。public void clearView(RecyclerView recyclerView, ViewHolder viewHolder)Item的操作并且Item的动画结束，此时我们应该恢复它的状态，以保证它被重新使用的时候能正确地展现。public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive)
Canvas：绘制RecyclerView的Canvas
dx, dy：偏移。actionState：拖拽还是侧滑，对应ACTION_STATE_DRAG和ACTION_STATE_SWIPE。isCurrentlyActive为true表示这个Item正在被用户所控制，false则表示它仅仅是在回到原本状态的动画过程当中。public void onChildDrawOver(Canvas c, RecyclerView recyclerView, ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive)
和上面类似，只不过它是绘制在Item之上。
如果我们希望使用系统默认的效果，那么只需要做以下几步：
继承于ItemTouchHelper.Callback编写自己的回调类，并在拖动和侧滑操作完成之后更新数据：
public class SimpleItemTouchHelper extends ItemTouchHelper.Callback {
private ItemTouchAdapter mAdapter;
public SimpleItemTouchHelper(ItemTouchAdapter adapter) {
mAdapter = adapter;
}
@Override
public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
Log.d("SimpleItemTouchHelper", "onSwiped, onMove, source=" + viewHolder.getAdapterPosition() + ",target=" + target.getAdapterPosition());
mAdapter.onItemDragged(viewHolder.getAdapterPosition(), target.getAdapterPosition());
return true;
}
@Override
public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
Log.d("SimpleItemTouchHelper", "onSwiped, direction=" + direction);
mAdapter.onItemSwiped(viewHolder.getAdapterPosition());
}
@Override
public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
return makeMovementFlags(ItemTouchHelper.UP | ItemTouchHelper.DOWN, ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT);
}
}编写数据操作的代码：
public class NormalAdapter extends RecyclerView.Adapter<NormalAdapter.NormalViewHolder> implements ItemTouchAdapter {
//......
@Override
public void onItemDragged(int from, int to) {
Collections.swap(mTitles, from, to);
notifyItemMoved(from, to);
}
@Override
public void onItemSwiped(int position) {
mTitles.remove(position);
notifyItemRemoved(position);
}
}ItemTouchHelper.Callback和RecyclerView关联起来，看注释中的1,2,3步：
private void init() {
List<String> titles = new ArrayList<>();
for (int i = 0; i < 20; i++) {
titles.add(String.valueOf(i));
}
LinearLayoutManager layoutManager = new LinearLayoutManager(this);
RecyclerView recyclerView = (RecyclerView) findViewById(R.id.rv_content);
recyclerView.setLayoutManager(layoutManager);
NormalAdapter adapter = new NormalAdapter(titles);
//1.自定义的ItemTouchHeloer.Callback
SimpleItemTouchHelper simpleItemTouchHelper = new
SimpleItemTouchHelper(adapter);
//2.利用这个Callback构造ItemTouchHelper
ItemTouchHelper itemTouchHelper = new ItemTouchHelper(simpleItemTouchHelper);
//3.把ItemTouchHelper和RecyclerView关联起来.
itemTouchHelper.attachToRecyclerView(recyclerView);
recyclerView.setAdapter(adapter);
}
当我们需要自定侧滑删除动画时，那么需要重写onChildDraw或者onChildDrawOver方法，在其中监听滑动距离的变化，并根据它来实时改变viewHolder中的UI，首先看效果：
首先，我们需要重写Item的布局，它包含两层，顶层是普通状态的标题文案，而底层则是蓝色底的删除提示：
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="66dp">
<!-- 删除提示 -->
<LinearLayout
android:id="@+id/ll_delete"
android:orientation="vertical"
android:gravity="center"
android:layout_gravity="end"
android:background="@android:color/holo_blue_dark"
android:paddingLeft="10dp"
android:paddingRight="10dp"
android:layout_width="wrap_content"
android:layout_height="match_parent">
<ImageView
android:src="@android:drawable/ic_input_delete"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
<TextView
android:text="delete"
android:textColor="@android:color/white"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</LinearLayout>
<!-- 普通文案 -->
<TextView
android:id="@+id/tv_title"
android:gravity="center"
android:background="@android:color/white"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</FrameLayout>接着，我们需要重写ItemTouchHelper.Callback：
public class AdvancedItemTouchHelper extends ItemTouchHelper.Callback {
private ItemTouchAdapter mAdapter;
public AdvancedItemTouchHelper(ItemTouchAdapter itemTouchAdapter) {
mAdapter = itemTouchAdapter;
}
@Override
public boolean isLongPressDragEnabled() {
return false;
}
@Override
public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
return makeMovementFlags(0, ItemTouchHelper.LEFT);
}
@Override
public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
mAdapter.onItemSwiped(viewHolder.getAdapterPosition());
}
@Override
public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
return false;
}
@Override
public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
super.clearView(recyclerView, viewHolder);
((NormalAdapter.NormalViewHolder) viewHolder).mTv.setTranslationX(0);
}
@Override
public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
NormalAdapter.NormalViewHolder mViewHolder = (NormalAdapter.NormalViewHolder) viewHolder;
int deleteWidth = mViewHolder.mDeleteLayout.getWidth();
float fraction = deleteWidth / (float) mViewHolder.itemView.getWidth();
mViewHolder.mTv.setTranslationX(dX * fraction);
}
}这里面有几点需要注意：
Item支持左滑删除，我们需要在getMovementFlags中返回ItemTouchHelper.LEFT标志位。onChildDraw当中，通过传入的dX动态改变了普通文案的translationX，使得底层的删除提示能够漏出。Adapter来删除数据。clearView中，需要把mTv重置为初始的状态。最后，我们按照前面的方法，把它和RecyclerView关联起来：
private void init() {
List<String> titles = new ArrayList<>();
for (int i = 0; i < 20; i++) {
titles.add("Item " + String.valueOf(i));
}
LinearLayoutManager layoutManager = new LinearLayoutManager(this);
RecyclerView recyclerView = (RecyclerView) findViewById(R.id.rv_content);
recyclerView.setLayoutManager(layoutManager);
NormalAdapter adapter = new NormalAdapter(titles);
AdvancedItemTouchHelper advancedItemTouchHelper = new AdvancedItemTouchHelper(adapter);
ItemTouchHelper itemTouchHelper = new ItemTouchHelper(advancedItemTouchHelper);
itemTouchHelper.attachToRecyclerView(recyclerView);
recyclerView.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL));
recyclerView.setAdapter(adapter);
}自定义RecyclerView的手势动画，关键是要理解ItemTouchHelper.Callback中各回调函数的含义，再通过回调函数中传入的数值来动态改变viewHolder中保存的itemView以及其子View的展现形式，就可以做出各种绚丽的效果。
RecyclerView 知识梳理(5) - ItemTouchHelper
标签：adapter 手势 public 重写 解析 pad lin log tle
原文地址：http://www.cnblogs.com/youseiraws/p/7071161.html
