Android 利用Matrix实现图片随手指平移、旋转、缩放

一、链接
Android 利用Matrix实现图片随手指平移、旋转、缩放—旋转

Android 利用Matrix实现图片随手指平移、旋转、缩放 —平移

Android 利用Matrix实现图片随手指平移、旋转、缩放—缩放

这篇是用来记录图片随手指缩放的。代码如下：

/**
 * 使用矩阵（Matrix）来设置图片的属性
 * 平移、旋转、放大缩小
 * 

 * 本类的效果：縮放
 * Created by lby on 2017/7/24.
 */

public class CropImageViewZoom extends AppCompatImageView {
    private Matrix matrix = new Matrix();
    private Matrix currentMatrix = new Matrix();
    private Bitmap bitmap;
    private float oldLength; //  按下時兩個落點的距離
    private PointF midPoint = new PointF();
    private boolean isMorePoint; // 是否是多根手指

    public CropImageViewZoom(Context context) {
        this(context, null);

    }

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

    }

    public CropImageViewZoom(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.aaa);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.save();
        canvas.drawBitmap(bitmap, matrix, null);
        canvas.restore();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // 注意：要想监听到ACTION_POINTER_DOWN和ACTION_POINTER_UP，必须有 MotionEvent.ACTION_MASK
        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
                isMorePoint = false;
                break;
            case MotionEvent.ACTION_POINTER_DOWN:
                isMorePoint = true;
                currentMatrix.set(matrix);
                oldLength = getLength(event);
                getMidPoint(midPoint, event);
                break;
            case MotionEvent.ACTION_MOVE:
                if (isMorePoint) {
                    matrix.set(currentMatrix);
                    // 计算缩放比例
                    float length = getLength(event) / oldLength;
                    matrix.postScale(length, length, midPoint.x, midPoint.y);
                }
                invalidate();
                break;
            case MotionEvent.ACTION_POINTER_UP:
                isMorePoint = false;
                break;
            case MotionEvent.ACTION_UP:
                break;
            default:
                break;
        }
        return true;
    }

    /**
     * 取手势中心点
     */
    private void getMidPoint(PointF point, MotionEvent event) {
        float x = event.getX(0) + event.getX(1);
        float y = event.getY(0) + event.getY(1);
        point.set(x / 2, y / 2);
    }

    /**
     * 获取两个落点之间的距离
     */
    private float getLength(MotionEvent event) {
        // 获取两个手指的点
        float pointX1 = event.getX(0);
        float pointX2 = event.getX(1);
        float pointY1 = event.getY(0);
        float pointY2 = event.getY(1);

        return (float) Math.sqrt(Math.pow(pointX1 - pointX2, 2) + Math.pow(pointY1 - pointY2, 2));
    }
}