ViewDragHelper 任意拖动

自定义view 拖动的边界需要严谨控制

view

public class DragView extends LinearLayout{

    private View childView;
    private ViewDragHelper mDragHelper;

    public DragView(Context context) {
        this(context, null);
    }

    public DragView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public DragView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initializeView();
    }

    private void initializeView() {
        mDragHelper = ViewDragHelper.create(this, new ViewDragHelper.Callback() {
            @Override
            public boolean tryCaptureView(View child, int pointerId) {
                return true;
            }

            @Override
            public int clampViewPositionVertical(View child, int top, int dy) {
                return Math.min(Math.max(top, 0), getHeight()-child.getHeight());
            }

            @Override
            public int clampViewPositionHorizontal(View child, int left, int dx) {
                return Math.min(getWidth() - child.getWidth(), Math.max(left, 0));
            }

            @Override
            public int getViewVerticalDragRange(View child) {
                return child.getMeasuredHeight();
            }

            @Override
            public int getViewHorizontalDragRange(View child) {
                return child.getMeasuredWidth();
            }

            @Override
            public void onEdgeDragStarted(int edgeFlags, int pointerId) {
                mDragHelper.captureChildView(childView,pointerId);
            }
        });
        mDragHelper.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        return mDragHelper.shouldInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        mDragHelper.processTouchEvent(event);
        return true;
    }

    @Override
    public void computeScroll() {
        if(mDragHelper.continueSettling(true)) {
            invalidate();
        }
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        if(getChildCount() < 1) {
            throw new IllegalArgumentException("必须有一个child");
        }
        childView = getChildAt(0);
    }
}

xml文件：

<cn.haoju.mytest.view.DragView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        >
        <Button
        android:layout_margin="10dp"
        android:gravity="center"
        android:layout_gravity="center"
        android:background="#aabbcc"
        android:text="拖我"
        android:layout_width="100dp"
        android:layout_height="100dp"/>

    </cn.haoju.mytest.view.DragView>

几行代码就可实现任意拖动了