android 图片的浏览、缩放、拖动和自动居中示例

android OpenGL 知识汇总
http://www.eoeandroid.com/thread-203299-1-1.html

检测手机wifi的状态
http://www.eoeandroid.com/thread-203307-1-1.html

GridView + ViewFlipper布局界面，模仿“机锋市场”
http://www.eoeandroid.com/thread-203252-1-1.html

直接上代码吧！文中写了比较详细的注释。

/** * 图片浏览、缩放、拖动、自动居中 */  

public class ImageTouch extends Activity implements OnTouchListener {  

    Matrix matrix = new Matrix();  

    Matrix savedMatrix = new Matrix();  

    DisplayMetrics dm;  

    ImageView imgView;  

    Bitmap bitmap;  

    float minScaleR;// 最小缩放比例  

    static final float MAX_SCALE = 4f;// 最大缩放比例  

    static final int NONE = 0;// 初始状态  

    static final int DRAG = 1;// 拖动  

    static final int ZOOM = 2;// 缩放  

    int mode = NONE;  

    PointF prev = new PointF();  

    PointF mid = new PointF();  

    float dist = 1f;  

  

    @Override  

    public void onCreate(Bundle savedInstanceState) {  

        super.onCreate(savedInstanceState);  

        setContentView(R.layout.main);  

        imgView = (ImageView) findViewById(R.id.imag);// 获取控件  

        // bitmap = BitmapFactory.decodeResource(getResources(),  

        // this.getIntent()  

        // .getExtras().getInt("IMG"));// 获取图片资源  

        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.image);// 获取图片资源  

        imgView.setImageBitmap(bitmap);// 填充控件  

        imgView.setOnTouchListener(this);// 设置触屏监听  

        dm = new DisplayMetrics();  

        getWindowManager().getDefaultDisplay().getMetrics(dm);// 获取分辨率  

        minZoom();  

        center();  

        imgView.setImageMatrix(matrix);  

    }  

  

    /** * 触屏监听 */  

    public boolean onTouch(View v, MotionEvent event) {  

        switch (event.getAction() & MotionEvent.ACTION_MASK) { // 主点按下  

        case MotionEvent.ACTION_DOWN:  

            savedMatrix.set(matrix);  

            prev.set(event.getX(), event.getY());  

            mode = DRAG;  

            break; // 副点按下  

        case MotionEvent.ACTION_POINTER_DOWN:  

            dist = spacing(event); // 如果连续两点距离大于10，则判定为多点模式  

            if (spacing(event) > 10f) {  

                savedMatrix.set(matrix);  

                midPoint(mid, event);  

                mode = ZOOM;  

            }  

            break;  

        case MotionEvent.ACTION_UP:  

        case MotionEvent.ACTION_POINTER_UP:  

            mode = NONE;  

            break;  

        case MotionEvent.ACTION_MOVE:  

            if (mode == DRAG) {  

                matrix.set(savedMatrix);  

                matrix.postTranslate(event.getX() - prev.x, event.getY()  

                        - prev.y);  

            } else if (mode == ZOOM) {  

                float newDist = spacing(event);  

                if (newDist > 10f) {  

                    matrix.set(savedMatrix);  

                    float tScale = newDist / dist;  

                    matrix.postScale(tScale, tScale, mid.x, mid.y);  

                }  

            }  

            break;  

        }  

        imgView.setImageMatrix(matrix);  

        CheckView();  

        return true;  

    }  

  

    /** * 限制最大最小缩放比例，自动居中 */  

    private void CheckView() {  

        float p[] = new float[9];  

        matrix.getValues(p);  

        if (mode == ZOOM) {  

            if (p[0] < minScaleR) {  

                matrix.setScale(minScaleR, minScaleR);  

            }  

            if (p[0] > MAX_SCALE) {  

                matrix.set(savedMatrix);  

            }  

        }  

        center();  

    }  

  

    /** * 最小缩放比例，最大为100% */  

    private void minZoom() {  

        minScaleR = Math.min(  

                (float) dm.widthPixels / (float) bitmap.getWidth(),  

                (float) dm.heightPixels / (float) bitmap.getHeight());  

        if (minScaleR < 1.0) {  

            matrix.postScale(minScaleR, minScaleR);  

        }  

    }  

  

    private void center() {  

        center(true, true);  

    }  

  

    /** * 横向、纵向居中 */  

    protected void center(boolean horizontal, boolean vertical) {  

        Matrix m = new Matrix();  

        m.set(matrix);  

        RectF rect = new RectF(0, 0, bitmap.getWidth(), bitmap.getHeight());  

        m.mapRect(rect);  

        float height = rect.height();  

        float width = rect.width();  

        float deltaX = 0, deltaY = 0;  

        if (vertical) {  

            // 图片小于屏幕大小，则居中显示。大于屏幕，上方留空则往上移，下放留空则往下移  

            int screenHeight = dm.heightPixels;  

            if (height < screenHeight) {  

                deltaY = (screenHeight - height) / 2 - rect.top;  

            } else if (rect.top > 0) {  

                deltaY = -rect.top;  

            } else if (rect.bottom < screenHeight) {  

                deltaY = imgView.getHeight() - rect.bottom;  

            }  

        }  

        if (horizontal) {  

            int screenWidth = dm.widthPixels;  

            if (width < screenWidth) {  

                deltaX = (screenWidth - width) / 2 - rect.left;  

            } else if (rect.left > 0) {  

                deltaX = -rect.left;  

            } else if (rect.right < screenWidth) {  

                deltaX = screenWidth - rect.right;  

            }  

        }  

        matrix.postTranslate(deltaX, deltaY);  

    }  

  

    /** * 两点的距离 */  

    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);  

    }  

  

    /** * 两点的中点 */  

    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);  

    }  

} 

main.xml

<?xml version="1.0" encoding="utf-8"?>  

    <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"  

        android:layout_width="fill_parent" android:layout_height="fill_parent"  

        android:layout_gravity="center">  

        <ImageView android:id="@+id/imag" android:layout_width="fill_parent"  

            android:layout_height="fill_parent" android:layout_gravity="center"  

            android:scaleType="matrix">  

        </ImageView>  

    </FrameLayout>