Android下图片的放大和缩小代码

/**
 *
 * @author chrp
 *
 *图片 的放大  缩小
 */
 
public class TouchImageViewActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        TouchImageView img = (TouchImageView) findViewById(R.id.snoop);
        img.setImageResource(R.drawable.snoopy);
        img.setMaxZoom(4f);
    }
}

public class TouchImageView extends ImageView {
 
    Matrix matrix;
 
    // We can be in one of these 3 states
    static final int NONE = 0;
    static final int DRAG = 1;
    static final int ZOOM = 2;
    int mode = NONE;
 
    // Remember some things for zooming
    PointF last = new PointF();
    PointF start = new PointF();
    float minScale = 1f;
    float maxScale = 3f;
    float[] m;
 
 
    int viewWidth, viewHeight;
    static final int CLICK = 3;
    float saveScale = 1f;
    protected float origWidth, origHeight;
    int oldMeasuredWidth, oldMeasuredHeight;
 
 
    ScaleGestureDetector mScaleDetector;
 
    Context context;
 
    public TouchImageView(Context context) {
        super(context);
        sharedConstructing(context);
    }
 
    public TouchImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        sharedConstructing(context);
    }
     
    private void sharedConstructing(Context context) {
        super.setClickable(true);
        this.context = context;
        mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
        matrix = new Matrix();
        m = new float[9];
        setImageMatrix(matrix);
        setScaleType(ScaleType.MATRIX);
 
        setOnTouchListener(new OnTouchListener() {
 
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                mScaleDetector.onTouchEvent(event);
                PointF curr = new PointF(event.getX(), event.getY());
 
                switch (event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        last.set(curr);
                        start.set(last);
                        mode = DRAG;
                        break;
                         
                    case MotionEvent.ACTION_MOVE:
                        if (mode == DRAG) {
                            float deltaX = curr.x - last.x;
                            float deltaY = curr.y - last.y;
                            float fixTransX = getFixDragTrans(deltaX, viewWidth, origWidth * saveScale);
                            float fixTransY = getFixDragTrans(deltaY, viewHeight, origHeight * saveScale);
                            matrix.postTranslate(fixTransX, fixTransY);
                            fixTrans();
                            last.set(curr.x, curr.y);
                        }
                        break;
 
                    case MotionEvent.ACTION_UP:
                        mode = NONE;
                        int xDiff = (int) Math.abs(curr.x - start.x);
                        int yDiff = (int) Math.abs(curr.y - start.y);
                        if (xDiff < CLICK && yDiff < CLICK)
                            performClick();
                        break;
 
                    case MotionEvent.ACTION_POINTER_UP:
                        mode = NONE;
                        break;
                }
                 
                setImageMatrix(matrix);
                invalidate();
                return true; // indicate event was handled
            }
 
        });
    }
 
    public void setMaxZoom(float x) {
        maxScale = x;
    }
 
    private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
        @Override
        public boolean onScaleBegin(ScaleGestureDetector detector) {
            mode = ZOOM;
            return true;
        }
 
        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            float mScaleFactor = detector.getScaleFactor();
            float origScale = saveScale;
            saveScale *= mScaleFactor;
            if (saveScale > maxScale) {
                saveScale = maxScale;
                mScaleFactor = maxScale / origScale;
            } else if (saveScale < minScale) {
                saveScale = minScale;
                mScaleFactor = minScale / origScale;
            }
 
            if (origWidth * saveScale <= viewWidth || origHeight * saveScale <= viewHeight)
                matrix.postScale(mScaleFactor, mScaleFactor, viewWidth / 2, viewHeight / 2);
            else
                matrix.postScale(mScaleFactor, mScaleFactor, detector.getFocusX(), detector.getFocusY());
 
            fixTrans();
            return true;
        }
    }
 
    void fixTrans() {
        matrix.getValues(m);
        float transX = m[Matrix.MTRANS_X];
        float transY = m[Matrix.MTRANS_Y];
         
        float fixTransX = getFixTrans(transX, viewWidth, origWidth * saveScale);
        float fixTransY = getFixTrans(transY, viewHeight, origHeight * saveScale);
 
        if (fixTransX != 0 || fixTransY != 0)
            matrix.postTranslate(fixTransX, fixTransY);
    }
 
    float getFixTrans(float trans, float viewSize, float contentSize) {
        float minTrans, maxTrans;
 
        if (contentSize <= viewSize) {
            minTrans = 0;
            maxTrans = viewSize - contentSize;
        } else {
            minTrans = viewSize - contentSize;
            maxTrans = 0;
        }
 
        if (trans < minTrans)
            return -trans + minTrans;
        if (trans > maxTrans)
            return -trans + maxTrans;
        return 0;
    }
     
    float getFixDragTrans(float delta, float viewSize, float contentSize) {
        if (contentSize <= viewSize) {
            return 0;
        }
        return delta;
    }
 
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        viewWidth = MeasureSpec.getSize(widthMeasureSpec);
        viewHeight = MeasureSpec.getSize(heightMeasureSpec);
         
        //
        // Rescales image on rotation
        //
        if (oldMeasuredHeight == viewWidth && oldMeasuredHeight == viewHeight
                || viewWidth == 0 || viewHeight == 0)
            return;
        oldMeasuredHeight = viewHeight;
        oldMeasuredWidth = viewWidth;
 
        if (saveScale == 1) {
            //Fit to screen.
            float scale;
 
            Drawable drawable = getDrawable();
            if (drawable == null || drawable.getIntrinsicWidth() == 0 || drawable.getIntrinsicHeight() == 0)
                return;
            int bmWidth = drawable.getIntrinsicWidth();
            int bmHeight = drawable.getIntrinsicHeight();
             
            Log.d("bmSize", "bmWidth: " + bmWidth + " bmHeight : " + bmHeight);
 
            float scaleX = (float) viewWidth / (float) bmWidth;
            float scaleY = (float) viewHeight / (float) bmHeight;
            scale = Math.min(scaleX, scaleY);
            matrix.setScale(scale, scale);
 
            // Center the image
            float redundantYSpace = (float) viewHeight - (scale * (float) bmHeight);
            float redundantXSpace = (float) viewWidth - (scale * (float) bmWidth);
            redundantYSpace /= (float) 2;
            redundantXSpace /= (float) 2;
 
            matrix.postTranslate(redundantXSpace, redundantYSpace);
 
            origWidth = viewWidth - 2 * redundantXSpace;
            origHeight = viewHeight - 2 * redundantYSpace;
            setImageMatrix(matrix);
        }
        fixTrans();
    }
}