可拖拽的ListView

说明： WindowManager在addView时尚未测量完成， 获取宽高都是0。 可以这样测量：

view.measure(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED);
int width = view.getMeasuredWidth();
1
2
使用getViewTreeObserver().addOnGlobalLayoutListener是布局完成后可以获取宽高；

public class DragListView extends ListView {

private WindowManager.LayoutParams windowParams;
private WindowManager windowManager;
private ImageView dragImageView;

private int offsetScreenTop; //距离屏幕顶部的位置
private int offsetViewTop; //手指按下位置距离item顶部的位置
private int dragPosition;

//上次点击按下的坐标
private int mLastMotionX, mLastMotionY;

private final int TOUCH_SLOP = 20;
private Runnable mLongPressRunnable;
private Bitmap mCurItemBmp;

//当前是否长按状态
private boolean mIsLongTouch;

public DragListView(Context context) {
super(context);
}

public DragListView(Context context, AttributeSet attrs) {
super(context, attrs);

mLongPressRunnable = new Runnable() {
@Override public void run() {
mIsLongTouch = true;

startDrag(mCurItemBmp, mLastMotionY);
}
};
}

//itemview里有view处理点击事件时， 当前ListView无法收到UP或CANCEL消息
@Override public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_UP
|| ev.getAction() == MotionEvent.ACTION_CANCEL) {
removeCallbacks(mLongPressRunnable);
stopDrag();
}
return super.dispatchTouchEvent(ev);
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
int x = (int) ev.getX();
int y = (int) ev.getY();
int rawY = (int) ev.getRawY();

if (ev.getAction() == MotionEvent.ACTION_DOWN) {
mLastMotionX = x;
mLastMotionY = y;
mIsLongTouch = false;
stopDrag(); //复位
removeCallbacks(mLongPressRunnable);

int currentPostion = dragPosition = pointToPosition(x, y);

//拖拽效果设置热区
if (currentPostion == AdapterView.INVALID_POSITION) {
return super.onInterceptTouchEvent(ev);
}
postDelayed(mLongPressRunnable, ViewConfiguration.getLongPressTimeout());

//getChildAt是获取可见位置的item
ViewGroup itemView = (ViewGroup) getChildAt(currentPostion - getFirstVisiblePosition());
offsetScreenTop = rawY - y;
offsetViewTop = y - itemView.getTop();

itemView.setDrawingCacheEnabled(true);// 开启cache.
mCurItemBmp = Bitmap.createBitmap(itemView.getDrawingCache());// 根据cache创建一个新的bitmap对象.
itemView.setDrawingCacheEnabled(false);// 一定关闭cache，否则复用会出现错乱
}
return super.onInterceptTouchEvent(ev);
}

@Override
public boolean onTouchEvent(MotionEvent ev) {
int y = (int) ev.getY();
int x = (int) ev.getX();
switch (ev.getAction()) {
case MotionEvent.ACTION_MOVE:
if (Math.abs(mLastMotionX - x) > TOUCH_SLOP
|| Math.abs(mLastMotionY - y) > TOUCH_SLOP) {
//滑动超过阈值时判定不是长按
removeCallbacks(mLongPressRunnable);
}

if (mIsLongTouch) {
onDrag(y);
getChildAt(dragPosition - getFirstVisiblePosition()).setVisibility(View.INVISIBLE);
return true; //避免列表滑动
}
removeCallbacks(mLongPressRunnable);
break;
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
removeCallbacks(mLongPressRunnable);
if (mIsLongTouch) {
stopDrag();
getChildAt(dragPosition - getFirstVisiblePosition()).setVisibility(View.VISIBLE);

mIsLongTouch = false;
}
break;
}

return super.onTouchEvent(ev);
}

private void startDrag(Bitmap bm, int y) {
int[] location = new int[2];
getLocationInWindow(location);

/***
* 初始化window.
*/
windowParams = new WindowManager.LayoutParams();
windowParams.gravity = Gravity.TOP|Gravity.LEFT;
windowParams.x = location[0];
windowParams.y = y - offsetViewTop + offsetScreenTop;
windowParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
windowParams.height = WindowManager.LayoutParams.WRAP_CONTENT;

windowParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE// 不需获取焦点
| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE// 不需接受触摸事件
| WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON// 保持设备常开，并保持亮度不变。
| WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN;// 窗口占满整个屏幕，忽略周围的装饰边框（例如状态栏）。此窗口需考虑到装饰边框的内容。

// windowParams.format = PixelFormat.TRANSLUCENT;// 默认为不透明，这里设成透明效果.
windowParams.windowAnimations = 0;// 窗口所使用的动画设置

ImageView imageView = new ImageView(getContext());
imageView.setImageBitmap(bm);
windowManager = (WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE);
windowManager.addView(imageView, windowParams);
dragImageView = imageView;
}

/**
* 拖动图像在ListView范围内， 不能超过边界
*
* @param y
*/
private void onDrag(int y) {
int offsetTop = y - offsetViewTop; //顶部不能出界
int offsetBottom = offsetViewTop + getHeight() - dragImageView.getHeight(); //下边界
if (dragImageView != null && offsetTop >= 0
&& offsetTop <= getChildAt(getChildCount() - 1).getTop()
&& y <= offsetBottom) {
windowParams.alpha = 0.8f;// 透明度
windowParams.y = y - offsetViewTop + offsetScreenTop;// 移动y值.//记得要加上dragOffset，windowManager计算的是整个屏幕.(标题栏和状态栏都要算上)
windowManager.updateViewLayout(dragImageView, windowParams);// 时时移动.
}

onChange(y);

scrollListView(y);
}

/**
* 同步滑动ListView
* @param y
*/
private void scrollListView(int y) {
View view = getChildAt(dragPosition - getFirstVisiblePosition());
int offsetY = mLastMotionY - y;

if (y < getHeight() / 3 && y < mLastMotionY) { //listview向上滑
setSelectionFromTop(dragPosition, offsetY + view.getTop());
} else if (y > getHeight() / 3 * 2 && y > mLastMotionY) { //listview向下滑
setSelectionFromTop(dragPosition, offsetY + view.getTop());
}
mLastMotionY = y;
}

/**
* 同步改变item的位置
* @param y
*/
private void onChange(int y) {
int currentPostion = pointToPosition(0, y);

if (currentPostion == AdapterView.INVALID_POSITION) {
currentPostion = dragPosition;
}

if (dragPosition != currentPostion) {
DragAdapter adapter = (DragAdapter) getAdapter();
adapter.change(dragPosition, currentPostion);
swich(dragPosition, currentPostion);
}

dragPosition = currentPostion;
}

/***
* 切换隐藏的位置
*/
private void swich(int start, int end) {
getChildAt(start - getFirstVisiblePosition(http://www.amjmh.com)).setVisibility(View.VISIBLE);
getChildAt(end - getFirstVisiblePosition()).setVisibility(View.INVISIBLE);
}

/**
* 停止拖动，删除影像
*/
public void stopDrag() {
if (dragImageView != null) {
windowManager.removeView(dragImageView);
dragImageView = null;
}
}
}
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