Android小應用----圖片的拖動、縮放

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matrix
	private Matrix newMatrix = new Matrix();//記錄手指正在拖動和縮放的matrix
	private 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
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		operImage= (ImageView) findViewById(R.id.before);
		operImage.setOnTouchListener(new OnTouchListener() {
			@Override
			public 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);
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

}