自定义可拖拽View(工具类ViewDragHelper的用法)

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android提供了GestureDetector

这个类用于常用手势识别, 如单击、双击、滑动等；对于拖拽手势的分析识别并不理性，

因此support-v4包提供了一个工具类ViewDragHelper, 使用此工具类可以轻松实现可拖拽View(准确的说应该是支持拖拽的View容器),

闲话少说, 请看代码:

DragContainerLayout.java

/** * ViewDragHelper的用法 * 1. ViewDragHelper.create()创建实例 * 2. 初始化callback * 3. 将当前ViewGroup的onInterceptTouchEvent和onTouchEvent事件委托给ViewDragHelper处理 * 4. 处理拖拽view的边界(在callback中的clampViewPositionHorizontal和clampViewPositionVertical方法中处理) */public class DragContainerLayout extends LinearLayout{    private ViewDragHelper mViewDragHelper;    public DragContainerLayout(Context context) {        super(context);        initViewDragHelper();        GestureDetector    }    public DragContainerLayout(Context context, AttributeSet attrs) {        super(context, attrs);        initViewDragHelper();    }    public DragContainerLayout(Context context, AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);        initViewDragHelper();    }    public DragContainerLayout(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {        super(context, attrs, defStyleAttr, defStyleRes);        initViewDragHelper();    }    private void initViewDragHelper() {        //ViewDragHelper.Callback是一个抽象类, 里面有更多的处理, 将需要处理的方法重写就可以了        mViewDragHelper = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback() {            @Override            public boolean tryCaptureView(View child, int pointerId) {                Log.e("abc", "pointerId=" + pointerId);                //第3个view不能截取事件 (也就是不能拖拽)                if(getChildCount() >= 3) {                    if(child == getChildAt(2)) {                        return false;                    }                }                return true; //true表示child可以拖拽, false标示child不能拖拽            }            @Override            public int clampViewPositionHorizontal(View child, int left, int dx) {                final int leftBound = getPaddingLeft();                final int rightBound = getWidth() - child.getWidth() - getPaddingRight();//                int newLeft = left;//                if(left < leftBound) newLeft = leftBound;//                if(left > rightBound) newLeft = rightBound;                //词句等价于上面的三句                int newLefth = Math.min(Math.max(left, leftBound), rightBound);                return newLefth;            }            @Override            public int clampViewPositionVertical(View child, int top, int dy) {                final int topBound = getPaddingTop();                final int bottomBound = getHeight() - child.getHeight() - getPaddingBottom();                int newTop = Math.min(bottomBound, Math.max(topBound, top));                return newTop;            }        });    }    @Override    public boolean onInterceptTouchEvent(MotionEvent ev) {        final int action = MotionEventCompat.getActionMasked(ev);        if(action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) {            mViewDragHelper.cancel();            return false;        }        return mViewDragHelper.shouldInterceptTouchEvent(ev);    }    @Override    public boolean onTouchEvent(MotionEvent event) {        mViewDragHelper.processTouchEvent(event);        return true;    }}

布局文件

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical" android:layout_width="match_parent"    android:layout_height="match_parent">    <com.stone.android_demo2.DragContainerLayout        android:layout_width="match_parent"        android:layout_height="match_parent"        android:orientation="vertical"        android:gravity="center"        android:paddingTop="60dp"        android:paddingLeft="0dp"        android:paddingBottom="0dp"        android:paddingRight="30dp">        <TextView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="Hello"            android:padding="10dp"            android:background="#4400ccaa"            android:layout_marginTop="10dp"/>        <TextView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="哈哈哈哈哈"            android:padding="10dp"            android:background="#4400ccaa"            android:layout_marginTop="10dp"/>        <TextView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="wakaka"            android:padding="10dp"            android:background="#4400ccaa"            android:layout_marginTop="10dp"/>        <TextView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="Hi, hi, you you !"            android:padding="10dp"            android:background="#4400ccaa"            android:layout_marginTop="10dp"/>    </com.stone.android_demo2.DragContainerLayout></LinearLayout>

创建一个Activity, 使用上述布局, 运行, 试试拖拽TextView

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