bitmap无限制放大,该怎么解决

import android.content.Context;import android.graphics.Matrix;import android.graphics.PointF;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.util.AttributeSet;import android.util.FloatMath;import android.view.GestureDetector;import android.view.MotionEvent;import android.view.View;import android.view.View.OnTouchListener;import android.widget.ImageView;public class DragImageView extends ImageView implements OnTouchListener {    // To get an GestureDetector will be used to get DoubleClickEvent    GestureDetector gd;    // These matrices will be used to move and zoom image    Matrix matrix = new Matrix();    Matrix savedMatrix = new 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;    // Dragable && Moveable    boolean Moveable = false;    boolean Dragable = false;    boolean Zoomable = false;    // Remember some things for zooming    PointF start = new PointF();    PointF end = new PointF();    PointF mid = new PointF();    float oldDist = 1f;    // size of drawable    float drawable_width;    float drawable_height;    // the point in the left and top on the screen    float x_point = 0.0f;    float y_point = 0.0f;    // the changed size of x and y    float x_change = 0.0f;    float y_change = 0.0f;    // the size of imageview    float imageview_width;    float imageview_height;    public DragImageView(Context context, AttributeSet attrs, int defStyle) {        super(context, attrs, defStyle);    }    public DragImageView(Context context, AttributeSet attrs) {        super(context, attrs);        this.setOnTouchListener(this);        gd = new GestureDetector(new mGesture());        setScaleType(ScaleType.MATRIX);        drawable_height = this.getDrawable().getIntrinsicHeight();        drawable_width = this.getDrawable().getIntrinsicWidth();//        Log.i("", "drawable_width=" + drawable_width);//        Log.i("", "drawable_height=" + drawable_height);    }    public DragImageView(Context context) {        super(context);    }    @Override    public boolean onTouch(View v, MotionEvent event) {        // To deal GestureEvent        gd.onTouchEvent(event);        imageview_width = v.getWidth();        imageview_height = v.getHeight();        // Handle touch events here...        switch (event.getAction() & MotionEvent.ACTION_MASK)/* 如果想监听多触点事件必须与Action_MASK相与 */{        case MotionEvent.ACTION_DOWN:            start.set(event.getX(), event.getY());            matrix.set(this.getImageMatrix());            savedMatrix.set(matrix);            mode = DRAG;            break;        case MotionEvent.ACTION_POINTER_DOWN:            oldDist = spacing(event);            if (oldDist > 10f) {                savedMatrix.set(matrix);                midPoint(mid, event);                mode = ZOOM;            }            break;        case MotionEvent.ACTION_UP:            if (Dragable) {/* 用来区分是单击还是拖动 */                x_point += (end.x - start.x);                y_point += (end.y - start.y);                Dragable = false;                decideAnimation(x_point, y_point);            }            mode = NONE;            break;        case MotionEvent.ACTION_POINTER_UP:            mode = NONE;            decideAnimation(x_point, y_point);            break;        case MotionEvent.ACTION_MOVE:            if (Moveable) {                if (mode == DRAG) {                    // ...                    matrix.set(savedMatrix);                    matrix.postTranslate(event.getX() - start.x, event.getY()                            - start.y);                    end.set(event.getX(), event.getY());                    Dragable = true;                } else if (mode == ZOOM) {                    Zoomable = true;                    float newDist = spacing(event);                    if (newDist > 10f) {                        matrix.set(savedMatrix);                        float scale = newDist / oldDist;                        matrix.postScale(scale, scale, mid.x, mid.y);                        // get the current size of drawable after zoomed                        if (scale > 1) {// When Enlarge                            drawable_width = drawable_width * scale                                    + drawable_width;                            drawable_height = drawable_height * scale                                    + drawable_height;                        } else { // When Narrow                            drawable_height = drawable_height - drawable_width                                    * scale;                            drawable_height = drawable_height - drawable_width                                    * scale;                        }                    }                }            }            break;        }        this.setImageMatrix(matrix);        return true;    }    // 两点间的距离    /**     * @param event     * @return float the distance of two point     * */    private float spacing(MotionEvent event) {        float x = event.getX(0) - event.getX(1);        float y = event.getY(0) - event.getY(1);        return FloatMath.sqrt(x * x + y * y);    }    // 两点的中心坐标    /**     * @param PointF     *            to record one point     * @param event     * */    private void midPoint(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);    }    /**     * the class extends GestureDetector to deal double tap     * */    private class mGesture extends GestureDetector.SimpleOnGestureListener {        @Override        public boolean onDoubleTap(MotionEvent e) {            Moveable = true;            return super.onDoubleTap(e);        }    }    // 判断有没有越界    /**     * @param x2     * @param y2     * @Descript the point in top and left     * */    public void decideAnimation(float x2, float y2) {        float top = imageview_height - drawable_height;        float left = imageview_width - drawable_width;//        Log.i("", "imageview_height=" + imageview_height + " imageview_width="//                + imageview_width);//        Log.i("", "drawable_height=" + drawable_height + " drawable_width="//                + drawable_width);//        Log.i("", "x2=" + x2 + "y2=" + y2);//        Log.i("", "left=" + left + "top=" + top);        if (drawable_width > imageview_width) {            if (x2 < left) {                x_point = left;            }            if (x2 > 0) {                x_point = 0;            }        }        if (drawable_height > imageview_height) {            if (y2 < top) {                y_point = top;            }            if (y2 > 0) {                y_point = 0;            }        }        if (drawable_width < imageview_width) {            if (x2 > left) {                x_point = left;            }            if (x2 < 0) {                x_point = 0;            }        }        if (drawable_height < imageview_height) {            if (y2 > top) {                y_point = top;            }            if (y2 < 0) {                y_point = 0;            }        }        // 发送动画请求        Message msg = new Message();        Bundle b = new Bundle();        b.putFloat("x_point", x_point);        b.putFloat("y_point", y_point);        msg.setData(b);        handler.sendMessageAtTime(msg, 100);    }    // 实现动画效果    Handler handler = new Handler() {        float temp_x;        float temp_y;        @Override        public void handleMessage(Message msg) {            super.handleMessage(msg);            Bundle b = msg.getData();            temp_x = b.getFloat("x_point");            temp_y = b.getFloat("y_point");//            Log.i("", "temp_x: " + temp_x + "temp_y: " + temp_y);            matrix.setTranslate(temp_x, temp_y);            setImageMatrix(matrix);        }    };}