工作中需要开发一个类似于抽屉式的滑动的 View，同过调研及查找资料发现ViewDragHelper可以实现此类方式，在此记录下ViewDragHelper的学习及使用。
首先 ViewDragHelper 分为三部：
- 创建
ViewDragHelper实例，通过
ViewDragHelper.create(ViewGroup forParent, float sensitivity, Callback cb)
创建ViewDragHelper实例，其中：
ViewGroup：当前的ViewGroup
sensitivity:设置滑动灵敏度，通常为 1
cb:拖拽回调，用来处理拖动位置相关回调 - 实现
ViewDragHelper.Callback()相关方法：
mViewDragHelper = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback() {
@Override
public boolean tryCaptureView(@NonNull View child, int pointerId) {
return false;
}
@Override
public int clampViewPositionVertical(@NonNull View child, int top, int dy) {
return super.clampViewPositionVertical(child, top, dy);
}
@Override
public int clampViewPositionHorizontal(@NonNull View child, int left, int dx) {
return super.clampViewPositionHorizontal(child, left, dx);
}
}
该回调可以移动相关的处理，比如哪些 view 可以移动，以及移动的边界处理等。其中参数如下：
-
tryCaptureView: 返回true表示捕获相关 View，根据传入的 child 确定要捕获的 view -
clampViewPositionVertical(View child, int top, int dy)、clampViewPositionHorizontal(View child, int left, int dx): child 移动边界控制，其中 top,left 表示移动到的位置。
- 处理
ViewGroup的触摸事件
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
return mViewDragHelper.shouldInterceptTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
mViewDragHelper.processTouchEvent(event);
return true;
}
onInterceptTouchEvent:交给 mViewDragHelper.shouldInterceptTouchEvent(ev) 进行处理
onTouchEvent：交给 mViewDragHelper.processTouchEvent(event) 进行处理
简单的使用就如上所示，当如，其中如果进行复杂的处理，还需更多的用法，比如：
- 边界触摸检测
- 拖拽释放回调
- 移动到某个指定位置
比如如下重写的方法：
mViewDragHelper = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback() {
@Override
public boolean tryCaptureView(@NonNull View child, int pointerId) {
return child == mDragView;
}
@Override
public int clampViewPositionVertical(@NonNull View child, int top, int dy) {
if (top > getHeight() - mDragViewHight) {
top = getHeight() - mDragViewHight;
} else if (top < MIN_TOP) {
top = MIN_TOP;
}
return top;
}
@Override
public int getViewVerticalDragRange(@NonNull View child) {
return getMeasuredHeight() - child.getMeasuredHeight();
}
@Override
public void onViewPositionChanged(@NonNull View changedView, int left, int top, int dx, int dy) {
super.onViewPositionChanged(changedView, left, top, dx, dy);
LinearLayout.LayoutParams bottomViewLayoutPara = (LayoutParams) mBottomView.getLayoutParams();
bottomViewLayoutPara.height = bottomViewLayoutPara.height + dy * -1;
mBottomView.setLayoutParams(bottomViewLayoutPara);
LinearLayout.LayoutParams topViewLayoutPara = (LayoutParams) mTopView.getLayoutParams();
topViewLayoutPara.height = topViewLayoutPara.height + dy;
mTopView.setLayoutParams(topViewLayoutPara);
}
});
}
其中：
-
getViewVerticalDragRange返回child 垂直移动范围的距离，如果不加，当有点击事件之后则不触发 -
onViewPositionChanged当位置改变进行回调
同时除了以上方法之外还有其余如下方法：
-
onViewDragStateChanged:ViewDragHelper状态改变时进行回调（IDLE,DRAGGING,SETTING） -
onEdgeTouched:触摸到边界是回调 -
onEdgeDragStarted:边界拖动时回调，需设置setEdgeTrackingEnabled(),可以设置如下- EDGE_LEFT：左边界
- EDGE_TOP：上边界
- EDGE_RIGHT：右边界
-
EDGE_BOTTOM：底部边界
附实现效果：
效果图
附代码（DragView）：
public class DragView extends LinearLayout {
private View mTopView;
private View mDragView;
private View mBottomView;
private ViewDragHelper mViewDragHelper;
private int mDragViewHight;
final int MIN_TOP = 100;
public DragView(Context context) {
super(context);
init();
}
public DragView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
init();
}
public DragView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
private void init() {
mViewDragHelper = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback() {
@Override
public boolean tryCaptureView(@NonNull View child, int pointerId) {
return child == mDragView;
}
@Override
public int clampViewPositionVertical(@NonNull View child, int top, int dy) {
if (top > getHeight() - mDragViewHight) {
top = getHeight() - mDragViewHight;
} else if (top < MIN_TOP) {
top = MIN_TOP;
}
return top;
}
@Override
public int getViewVerticalDragRange(@NonNull View child) {
return getMeasuredHeight() - child.getMeasuredHeight();
}
@Override
public void onViewPositionChanged(@NonNull View changedView, int left, int top, int dx, int dy) {
super.onViewPositionChanged(changedView, left, top, dx, dy);
LinearLayout.LayoutParams bottomViewLayoutPara = (LayoutParams) mBottomView.getLayoutParams();
bottomViewLayoutPara.height = bottomViewLayoutPara.height + dy * -1;
mBottomView.setLayoutParams(bottomViewLayoutPara);
LinearLayout.LayoutParams topViewLayoutPara = (LayoutParams) mTopView.getLayoutParams();
topViewLayoutPara.height = topViewLayoutPara.height + dy;
mTopView.setLayoutParams(topViewLayoutPara);
}
});
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
return mViewDragHelper.shouldInterceptTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
mViewDragHelper.processTouchEvent(event);
return true;
}
@Override
protected void onFinishInflate() {
super.onFinishInflate();
mTopView = getChildAt(0);
mDragView = getChildAt(1);
mBottomView = getChildAt(2);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
mDragViewHight = mDragView.getMeasuredHeight();
}
}
