Android 自定义View可拖动移动位置及边缘拉伸放大缩(转)

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;

 

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();

   
    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;
    }

   
    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);