Android 自定义View可拖动移动位置及边缘拉伸放大缩小

　　一.首先说一下定义这样一个View有什么用?在一些app中,需要设置头像,而用户选择的图片可能是使用摄像头拍摄,也可能是选择的相册里面的图片,总之,这样的图片大小不一,就比如在使用某个聊天软件的时候,设置头像,需要对图片进行截取.

　　要实现这样一个功能,首先,需要分析用户的操作,即用户所点击的View的位置,如下图,我把View分为9个区域,

• 当ACTION_DOWN时如果坐标为1.2.3.4四个区域,则对View进行相应的左上/右上/左下/右下拉伸;
• 当ACTION_DOWN时如果坐标为5.6.7.8四个区域,则分别对上/右/下/左四个方向进行拉伸;
• 当ACTION_DOWN时如果坐标为9这个区域,则对View进行移动;

　　理论分析完成,下面来看具体实现;

　　在下面的类中,有五个方法center/left/top/bottom/right分别对应移动/向左拉伸/向上拉伸/向下拉伸/向右拉伸,当Action_down为1-4所在的区域时,组合前面的对应的两个拉伸方法即可,如左上角拉伸则对应执行left+top方法,这也是把四个单独一条边的边缘拉伸独立出来的原因;

　　在View中,我设定了View的最小宽度和高度,都是200,所以当用户点击边缘进行缩小操作时,能缩小的最小值也就是200;分别在left/top/bottom/right中体现;

/**
 * @see http://www.cnblogs.com/a284628487/
 * @author Cj
 *
 */
public class DragScaleView extends View implements OnTouchListener {
    protected int screenWidth;
    protected int screenHeight;
    protected int lastX;
    protected int lastY;
    private int oriLeft;
    private int oriRight;
    private int oriTop;
    private int oriBottom;
    private int dragDirection;
    private static final int TOP = 0x15;
    private static final int LEFT = 0x16;
    private static final int BOTTOM = 0x17;
    private static final int RIGHT = 0x18;
    private static final int LEFT_TOP = 0x11;
    private static final int RIGHT_TOP = 0x12;
    private static final int LEFT_BOTTOM = 0x13;
    private static final int RIGHT_BOTTOM = 0x14;
    private static final int CENTER = 0x19;
    private int offset = 20;
    protected Paint paint = new Paint();

    /**
     * 初始化获取屏幕宽高
     */
    protected void initScreenW_H() {
        screenHeight = getResources().getDisplayMetrics().heightPixels - 40;
        screenWidth = getResources().getDisplayMetrics().widthPixels;
    }

    public DragScaleView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        setOnTouchListener(this);
        initScreenW_H();
    }

    public DragScaleView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setOnTouchListener(this);
        initScreenW_H();
    }

    public DragScaleView(Context context) {
        super(context);
        setOnTouchListener(this);
        initScreenW_H();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        paint.setColor(Color.RED);
        paint.setStrokeWidth(4.0f);
        paint.setStyle(Style.STROKE);
        canvas.drawRect(offset, offset, getWidth() - offset, getHeight()
                - offset, paint);
    }

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        int action = event.getAction();
        if (action == MotionEvent.ACTION_DOWN) {
            oriLeft = v.getLeft();
            oriRight = v.getRight();
            oriTop = v.getTop();
            oriBottom = v.getBottom();
            lastY = (int) event.getRawY();
            lastX = (int) event.getRawX();
            dragDirection = getDirection(v, (int) event.getX(),
                    (int) event.getY());
        }
        // 处理拖动事件
        delDrag(v, event, action);
        invalidate();
        return false;
    }

    /**
     * 处理拖动事件
     *
     * @param v
     * @param event
     * @param action
     */
    protected void delDrag(View v, MotionEvent event, int action) {
        switch (action) {
        case MotionEvent.ACTION_MOVE:
            int dx = (int) event.getRawX() - lastX;
            int dy = (int) event.getRawY() - lastY;
            switch (dragDirection) {
            case LEFT: // 左边缘
                left(v, dx);
                break;
            case RIGHT: // 右边缘
                right(v, dx);
                break;
            case BOTTOM: // 下边缘
                bottom(v, dy);
                break;
            case TOP: // 上边缘
                top(v, dy);
                break;
            case CENTER: // 点击中心-->>移动
                center(v, dx, dy);
                break;
            case LEFT_BOTTOM: // 左下
                left(v, dx);
                bottom(v, dy);
                break;
            case LEFT_TOP: // 左上
                left(v, dx);
                top(v, dy);
                break;
            case RIGHT_BOTTOM: // 右下
                right(v, dx);
                bottom(v, dy);
                break;
            case RIGHT_TOP: // 右上
                right(v, dx);
                top(v, dy);
                break;
            }
            if (dragDirection != CENTER) {
                v.layout(oriLeft, oriTop, oriRight, oriBottom);
            }
            lastX = (int) event.getRawX();
            lastY = (int) event.getRawY();
            break;
        case MotionEvent.ACTION_UP:
            dragDirection = 0;
            break;
        }
    }

    /**
     * 触摸点为中心->>移动
     *
     * @param v
     * @param dx
     * @param dy
     */
    private void center(View v, int dx, int dy) {
        int left = v.getLeft() + dx;
        int top = v.getTop() + dy;
        int right = v.getRight() + dx;
        int bottom = v.getBottom() + dy;
        if (left < -offset) {
            left = -offset;
            right = left + v.getWidth();
        }
        if (right > screenWidth + offset) {
            right = screenWidth + offset;
            left = right - v.getWidth();
        }
        if (top < -offset) {
            top = -offset;
            bottom = top + v.getHeight();
        }
        if (bottom > screenHeight + offset) {
            bottom = screenHeight + offset;
            top = bottom - v.getHeight();
        }
        v.layout(left, top, right, bottom);
    }

    /**
     * 触摸点为上边缘
     *
     * @param v
     * @param dy
     */
    private void top(View v, int dy) {
        oriTop += dy;
        if (oriTop < -offset) {
            oriTop = -offset;
        }
        if (oriBottom - oriTop - 2 * offset < 200) {
            oriTop = oriBottom - 2 * offset - 200;
        }
    }

    /**
     * 触摸点为下边缘
     *
     * @param v
     * @param dy
     */
    private void bottom(View v, int dy) {
        oriBottom += dy;
        if (oriBottom > screenHeight + offset) {
            oriBottom = screenHeight + offset;
        }
        if (oriBottom - oriTop - 2 * offset < 200) {
            oriBottom = 200 + oriTop + 2 * offset;
        }
    }

    /**
     * 触摸点为右边缘
     *
     * @param v
     * @param dx
     */
    private void right(View v, int dx) {
        oriRight += dx;
        if (oriRight > screenWidth + offset) {
            oriRight = screenWidth + offset;
        }
        if (oriRight - oriLeft - 2 * offset < 200) {
            oriRight = oriLeft + 2 * offset + 200;
        }
    }

    /**
     * 触摸点为左边缘
     *
     * @param v
     * @param dx
     */
    private void left(View v, int dx) {
        oriLeft += dx;
        if (oriLeft < -offset) {
            oriLeft = -offset;
        }
        if (oriRight - oriLeft - 2 * offset < 200) {
            oriLeft = oriRight - 2 * offset - 200;
        }
    }

    /**
     * 获取触摸点flag
     *
     * @param v
     * @param x
     * @param y
     * @return
     */
    protected int getDirection(View v, int x, int y) {
        int left = v.getLeft();
        int right = v.getRight();
        int bottom = v.getBottom();
        int top = v.getTop();
        if (x < 40 && y < 40) {
            return LEFT_TOP;
        }
        if (y < 40 && right - left - x < 40) {
            return RIGHT_TOP;
        }
        if (x < 40 && bottom - top - y < 40) {
            return LEFT_BOTTOM;
        }
        if (right - left - x < 40 && bottom - top - y < 40) {
            return RIGHT_BOTTOM;
        }
        if (x < 40) {
            return LEFT;
        }
        if (y < 40) {
            return TOP;
        }
        if (right - left - x < 40) {
            return RIGHT;
        }
        if (bottom - top - y < 40) {
            return BOTTOM;
        }
        return CENTER;
    }

    /**
     * 获取截取宽度
     *
     * @return
     */
    public int getCutWidth() {
        return getWidth() - 2 * offset;
    }

    /**
     * 获取截取高度
     *
     * @return
     */
    public int getCutHeight() {
        return getHeight() - 2 * offset;
    }
}

　　二.使用View,如果想要对View进行移动,需要在xml中配置android:clickable="true"属性;

    <xxx.DragScaleView
        android:id="@+id/ds"
        android:layout_width="180dip"
        android:layout_height="180dip"
        android:clickable="true" />

　　三.效果图,右图是拉伸后的效果
  

　　四.关于MotionEvent.getX()和MotionEvent.getRawX()的区别

　　getX表示触摸点距离View的左边缘的距离,而getRawX表示触摸点距离手机屏幕左侧的距离;