Android RecyclerView宫格拖拽效果实现
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搜狐技术产品约 11 分钟
搜狐技术产品约 11 分钟
作者：时光少年
链接： https://juejin.cn/post/7348707728921853971
来源：稀土掘金
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。 01 前言
在 Android 发展的进程中，网格布局一直比较有热度，其中一个原因是对用户来说便捷操作，对 app 厂商而言也会带来很多的曝光量，对于很多头部 app ，展示网格菜单几乎是必选项。实现网格的方式有很多种，比如 GridView 、 GridLayout ， TableLayou t等，实际上，由于 RecyclerView 的灵活性和可扩展性很高，这些 View 基本没必要去学了，为什么这样说呢？主要原因是基于 RecyclerView 可以实现很多布局效果，传统的很多 Layout 都可以通过 RecyclerView 去实现，比如 ViewPage r 、 SlideTabLayout 、 DrawerLayout 、 ListView 等，甚至连九宫格解锁效果也可以实现。 在很早之前，实现网格的拖拽效果主要是通过 G ridView 去实现的，如果列数为 1 的话，那么 GridView 基本上就实现了 ListView 一样的上下拖拽。 话说回来，我们现在基本不用去学习这类实现了，因为 RecyclerView 足够强大，通过简单的数据组装，是完全可以替代 GridView 和 ListView 的。 02 效果 本篇我们会使用 R ecyclerView 来实现网格拖拽，本篇将结合图片分片案例，实现拖拽效果：
如果要实现网格菜单的拖拽，也是可以使用这种方式的，只要你的想象丰富，理论上我们借助 RecyclerView 其实可以做出很多效果：
03 拖拽效果原理
拖动其实需要处理 3 个核心的问题 ： 事件处理、图像平移、数据交换。 04 事件处理 实际上无论传统的拖拽效果还是最新的拖拽效果，都离不开事件处理，不过，好处就是， go ogle 为 RecyclerView 提供了 ItemTouchHelper 来处理这个问题，相比传统的 GridView 实现方式，省去了很多事情，如动画、目标查找等。不过，我们回顾下原理，其实他们很多方面都是相似的，不同之处就是 ItemTouchHelper 设计的非常好用，而且接口暴露的非常彻底，甚至能决定哪些 View 可以拖动、哪些 view 不能拖动，哪些 View 可以删除，以及什么方向可以拖动，如果我们上、下、左、右四个方向都选中的话，斜对角拖动完全没问题， 事件处理这里， GridView 使用的方式相对传统，而 ItemTouchHelper 借助 RecyclerView 的一个接口（看样子是开的后门），通过 View 自身去拦截事件。
public interface OnItemTouchListener {
//是否让RecyclerView拦截事件
boolean onInterceptTouchEvent(@NonNull RecyclerView rv, @NonNull MotionEvent e);
//拦截之后处理RecyclerView的事件
void onTouchEvent(@NonNull RecyclerView rv, @NonNull MotionEvent e);
//监听禁止拦截事件的请求结果
void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept);
}
class ItemTouchUIUtilImpl implements ItemTouchUIUtil {
static final ItemTouchUIUtil INSTANCE = new ItemTouchUIUtilImpl();
@Override
public void onDraw(Canvas c, RecyclerView recyclerView, View view, float dX, float dY,
int actionState, boolean isCurrentlyActive) {
if (Build.VERSION.SDK_INT >= 21) {
if (isCurrentlyActive) {
Object originalElevation = view.getTag(R.id.item_touch_helper_previous_elevation);
if (originalElevation == null) {
originalElevation = ViewCompat.getElevation(view);
float newElevation = 1f + findMaxElevation(recyclerView, view);
ViewCompat.setElevation(view, newElevation);
view.setTag(R.id.item_touch_helper_previous_elevation, originalElevation);
}
}
}
view.setTranslationX(dX);
view.setTranslationY(dY);
}
//省略一些有关或者无关的代码
}
View#getChildDrawingOrder(...)
void drawChildFunction(drawIndex,canvas){
children[mapChildIndex(drawIndex)].draw(canvas);
}
ArrayList<View> buildOrderedChildList() {
final int childrenCount = mChildrenCount;
if (childrenCount <= 1 || !hasChildWithZ()) return null;
if (mPreSortedChildren == null) {
mPreSortedChildren = new ArrayList<>(childrenCount);
} else {
// callers should clear, so clear shouldn't be necessary, but for safety...
mPreSortedChildren.clear();
mPreSortedChildren.ensureCapacity(childrenCount);
}
final boolean customOrder = isChildrenDrawingOrderEnabled();
for (int i = 0; i < childrenCount; i++) {
// add next child (in child order) to end of list
final int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder);
// 映射View
final View nextChild = mChildren[childIndex];
final float currentZ = nextChild.getZ();
// 如果Z值大的话往后移动，5.0之前的代码没有这段
int insertIndex = i;
while (insertIndex > 0 && mPreSortedChildren.get(insertIndex - 1).getZ() > currentZ) {
insertIndex--;
}
mPreSortedChildren.add(insertIndex, nextChild);
}
return mPreSortedChildren;
}
private void addChildDrawingOrderCallback() {
if (Build.VERSION.SDK_INT >= 21) {
return; // we use elevation on Lollipop
}
if (mChildDrawingOrderCallback == null) {
mChildDrawingOrderCallback = new RecyclerView.ChildDrawingOrderCallback() {
@Override
public int onGetChildDrawingOrder(int childCount, int i) {
if (mOverdrawChild == null) {
return i;
}
int childPosition = mOverdrawChildPosition;
if (childPosition == -1) {
childPosition = mRecyclerView.indexOfChild(mOverdrawChild);
mOverdrawChildPosition = childPosition;
}
if (i == childCount - 1) {
//将最后索引位置展示被拖拽的View
return childPosition;
}
//后面的View 绘制顺序往前移动
return i < childPosition ? i : i + 1;
}
};
}
mRecyclerView.setChildDrawingOrderCallback(mChildDrawingOrderCallback);
}
@Override
public boolean onItemMove(int fromPosition, int toPosition) {
Collections.swap(mDataList, fromPosition, toPosition);
notifyItemMoved(fromPosition, toPosition);
return true;
}
@Override
public void clearView(View view) {
if (Build.VERSION.SDK_INT >= 21) {
final Object tag = view.getTag(R.id.item_touch_helper_previous_elevation);
if (tag instanceof Float) {
ViewCompat.setElevation(view, (Float) tag);
}
view.setTag(R.id.item_touch_helper_previous_elevation, null);
}
view.setTranslationX(0f);
view.setTranslationY(0f);
}
Bitmap srcInputBitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.image_4);
Bitmap source = Bitmap.createScaledBitmap(srcInputBitmap, width, height, true);
srcInputBitmap.recycle();
int colCount = spanCount;
int rowCount = 6;
int spanImageWidthSize = source.getWidth() / colCount;
int spanImageHeightSize = (source.getHeight() - rowCount * padding/2) / rowCount;
Bitmap[] bitmaps = new Bitmap[rowCount * colCount];
for (int i = 0; i < rowCount; i++) {
for (int j = 0; j < colCount; j++) {
int y = i * spanImageHeightSize;
int x = j * spanImageWidthSize;
Bitmap bitmap = Bitmap.createBitmap(source, x, y, spanImageWidthSize, spanImageHeightSize);
bitmaps[i * colCount + j] = bitmap;
}
}
public class SimpleItemDecoration extends RecyclerView.ItemDecoration {
public int delta;
public SimpleItemDecoration(int padding) {
delta = padding;
}
@Override
public void getItemOffsets(Rect outRect, View view,
RecyclerView parent, RecyclerView.State state) {
int position = parent.getChildAdapterPosition(view);
RecyclerView.Adapter adapter = parent.getAdapter();
int viewType = adapter.getItemViewType(position);
if(viewType== Bean.TYPE_GROUP){
return;
}
GridLayoutManager layoutManager = (GridLayoutManager) parent.getLayoutManager();
//列数量
int cols = layoutManager.getSpanCount();
//position转为在第几列
int current = layoutManager.getSpanSizeLookup().getSpanIndex(position,cols);
//可有可无
int currentCol = current % cols;
int bottomPadding = delta / 2;
if (currentCol == 0) { //第0列左侧贴边
outRect.left = 0;
outRect.right = delta / 4;
outRect.bottom = bottomPadding;
} else if (currentCol == cols - 1) {
outRect.left = delta / 4;
outRect.right = 0;
outRect.bottom = bottomPadding;
//最后一列右侧贴边
} else {
outRect.left = delta / 4;
outRect.right = delta / 4;
outRect.bottom = bottomPadding;
}
}
}
mLinearLayoutManager = new GridLayoutManager(this, spanCount, LinearLayoutManager.VERTICAL, false);
mLinearLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup(){
@Override
public int getSpanSize(int position) {
if(mAdapter.getItemViewType(position) == Bean.TYPE_GROUP){
return spanCount;
}
return 1;
}
});
mAdapter = new RecyclerViewAdapter();
mRecyclerView.setAdapter(mAdapter);
mRecyclerView.setLayoutManager(mLinearLayoutManager);
mRecyclerView.addItemDecoration(new SimpleItemDecoration(padding));
ItemTouchHelper itemTouchHelper = new ItemTouchHelper(new GridItemTouchCallback(mAdapter));
itemTouchHelper.attachToRecyclerView(mRecyclerView);
public class GridItemTouchCallback extends ItemTouchHelper.Callback {
private final ItemTouchCallback mItemTouchCallback;
public GridItemTouchCallback(ItemTouchCallback itemTouchCallback) {
mItemTouchCallback = itemTouchCallback;
}
@Override
public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
if(viewHolder.getItemViewType() == Bean.TYPE_GROUP){
return 0; //设置此类型的View不可拖动
}
// 上下左右拖动
int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
return makeMovementFlags(dragFlags, 0);
}
@Override
public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
// 通知Adapter移动View
return mItemTouchCallback.onItemMove(viewHolder.getAdapterPosition(), target.getAdapterPosition());
}
@Override
public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
// 通知Adapter删除View
mItemTouchCallback.onItemRemove(viewHolder.getAdapterPosition());
}
@Override
public void onChildDraw(@NonNull Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
}
@Override
public void onChildDrawOver(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
Log.d("GridItemTouch","dx="+dX+", dy="+dY);
super.onChildDrawOver(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
}
}
public static int makeMovementFlags(int dragFlags, int swipeFlags) {
return makeFlag(ACTION_STATE_IDLE, swipeFlags | dragFlags)
| makeFlag(ACTION_STATE_SWIPE, swipeFlags)
| makeFlag(ACTION_STATE_DRAG, dragFlags);
}
public class GridDragActivity extends Activity {
RecyclerView mRecyclerView;
RecyclerViewAdapter mAdapter;
private LinearLayoutManager mLinearLayoutManager = null;
HandlerThread handlerThread = new HandlerThread("GridDragActivity");
private final int spanCount = 5;
private final int padding = 10;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.drag_activity);
mRecyclerView = findViewById(R.id.recyclerView);
mLinearLayoutManager = new GridLayoutManager(this, spanCount, LinearLayoutManager.VERTICAL, false);
mAdapter = new RecyclerViewAdapter();
mRecyclerView.setAdapter(mAdapter);
mRecyclerView.setLayoutManager(mLinearLayoutManager);
mRecyclerView.addItemDecoration(new SimpleItemDecoration(padding));
ItemTouchHelper itemTouchHelper = new ItemTouchHelper(new GridItemTouchCallback(mAdapter));
itemTouchHelper.attachToRecyclerView(mRecyclerView);
handlerThread.start();
mRecyclerView.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
@Override
public boolean onPreDraw() {
mRecyclerView.getViewTreeObserver().removeOnPreDrawListener(this);
loadData();
return false;
}
});
}
@Override
protected void onDestroy() {
handlerThread.quitSafely();
super.onDestroy();
}
private void loadData() {
Handler handler = new Handler(handlerThread.getLooper());
handler.post(new Runnable() {
@Override
public void run() {
int width = mRecyclerView.getWidth();
int height = mRecyclerView.getHeight();
Bitmap srcInputBitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.image_4);
Bitmap source = Bitmap.createScaledBitmap(srcInputBitmap, width, height, true);
srcInputBitmap.recycle();
int colCount = spanCount;
int rowCount = 6;
int spanImageWidthSize = source.getWidth() / colCount;
int spanImageHeightSize = (source.getHeight() - rowCount * padding / 2) / rowCount;
Bitmap[] bitmaps = new Bitmap[rowCount * colCount];
for (int i = 0; i < rowCount; i++) {
for (int j = 0; j < colCount; j++) {
int y = i * spanImageHeightSize;
int x = j * spanImageWidthSize;
Bitmap bitmap = Bitmap.createBitmap(source, x, y, spanImageWidthSize, spanImageHeightSize);
bitmaps[i * colCount + j] = bitmap;
}
}
List<Bean> beans = generateDataList(rowCount * colCount, bitmaps);
runOnUiThread(new Runnable() {
@Override
public void run() {
mAdapter.setDataList(beans);
}
});
}
});
}
private List<Bean> generateDataList(int count, Bitmap[] bitmaps) {
List<Bean> dataList = new ArrayList<>();
for (int i = 0; i < count; i++) {
Bean bean = new Bean();
bean.setString("" + i);
bean.setBitmap(bitmaps[i]);
bean.setColor(Color.parseColor(ColorUtils.generateRandomColor()));
dataList.add(bean);
}
return dataList;
}
}