Android小應用----圖片的拖動、縮放

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public class MainActivity extends Activity {private ImageView operImage;private PointF point = new PointF();//記錄手指的位置private PointF midPoint = new PointF();//記錄手指間的中點的位置private Matrix matrix = new Matrix();//記錄拖動和縮放前手指按下的matrixprivate Matrix newMatrix = new Matrix();//記錄手指正在拖動和縮放的matrixprivate int type = 0;//操作類型private float pointerDistance;//兩個手指的距離private static final int DRAG = 1;//拖動private static final int SCALE = 2;//縮放@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);operImage= (ImageView) findViewById(R.id.before);operImage.setOnTouchListener(new OnTouchListener() {@Overridepublic boolean onTouch(View v, MotionEvent event) {int action = event.getAction()&MotionEvent.ACTION_MASK;switch (action) {case MotionEvent.ACTION_DOWN:float startX =  event.getX();float startY =  event.getY();//記錄手指的位置point.set(startX, startY);//得到當前圖片的位置matrix.set(operImage.getImageMatrix());type = DRAG;//拖動break;case MotionEvent.ACTION_POINTER_1_DOWN://記錄圖片沒有縮放前的大小matrix.set(operImage.getImageMatrix());//記錄兩個手指的距離pointerDistance = getDistance(event);//記錄兩個手指距離的中點midPoint= getMidPoint(event);type = SCALE;//縮放break;case MotionEvent.ACTION_MOVE:switch (type) {case DRAG://拖動float newX =  event.getX();float newY =  event.getY();newMatrix.set(matrix);float dx = newX - point.x;float dy = newY - point.y;newMatrix.postTranslate(dx, dy);break;case SCALE://縮放newMatrix.set(matrix);float nowDistance = getDistance(event);//根據此時的兩個手指間的距離除以開始的兩個手指間的距離計算縮放比float scale = nowDistance/pointerDistance;//根據中心點進行縮放newMatrix.postScale(scale, scale, midPoint.x, midPoint.y);break;default:break;}break;case MotionEvent.ACTION_UP:type = 0;break;case MotionEvent.ACTION_POINTER_1_UP:type = 0;break;}operImage.setImageMatrix(newMatrix);return true;}});}/* * 計算兩個手指的中點 */protected PointF getMidPoint(MotionEvent event) {float x = (event.getX(1) + event.getX(0))/2;float y = (event.getY(1) + event.getY(0))/2;return new PointF(x, y);}/* * 計算兩點間的距離 */protected float getDistance(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);}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {getMenuInflater().inflate(R.menu.main, menu);return true;}}