ViewDragHelper学习及使用

2019-03-24 本文已影响0人彡Panda彡

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();
    }
}

ViewDragHelper学习及使用

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