android中图片的拖拉和缩放

落日映苍穹つ 2022-08-06 11:07 148阅读 0赞

首先是布局文件，引入图片

activity

package cn.wonders.drag;
    
    import android.support.v7.app.ActionBarActivity;
    import android.view.MotionEvent;
    import android.view.View;
    import android.view.View.OnTouchListener;
    import android.widget.ImageView;
    import android.graphics.Matrix;
    import android.graphics.PointF;
    import android.os.Bundle;
    
    public class MainActivity extends ActionBarActivity {
    	private ImageView imageView;
    	
    	@Override
    	protected void onCreate(Bundle savedInstanceState) {
    		super.onCreate(savedInstanceState);
    		setContentView(R.layout.activity_main);
    
    		imageView = (ImageView) findViewById(R.id.imageView);
    		imageView.setOnTouchListener(new TonchListener());
    	}
    
    	private final class TonchListener implements OnTouchListener {
    		private PointF startPoint = new PointF();
    		private Matrix matrix = new Matrix();
    		//照片当前的移动位子
    		private Matrix currentMatrix = new Matrix();
    		//模式
    		private int mode = 0;
    		//拖拉
    		private final static int GRAG = 1;
    		//多点触摸
    		private final static int ZOOM = 2;
    		//开始时2根手指的距离
    		private float startDis;
    		//中间点
    		private PointF midPoint;
    		
    		@Override
    		public boolean onTouch(View v, MotionEvent event) {
    			//取后8位
    			switch (event.getAction() & MotionEvent.ACTION_MASK) {
    			case MotionEvent.ACTION_DOWN:
    				//第一次按下时记录坐标
    				mode = GRAG;
    				currentMatrix.set(imageView.getImageMatrix());
    				startPoint.set(event.getX(), event.getY());
    				break;
    				
    			case MotionEvent.ACTION_MOVE:
    				if(mode == GRAG) {
    					float dx = event.getX() - startPoint.x;
    					float dy = event.getY() - startPoint.y;
    					//实现位子的移动,在上一次的基础上移动
    					matrix.set(currentMatrix);
    					matrix.postTranslate(dx, dy);
    				}else if (mode == ZOOM) {//缩放
    					float endDis = distance(event);
    					//得到缩放倍数
    					if(endDis > 10f) {
    						float scale = endDis/startDis;
    						//参数：x和y轴的放大倍数，以及中心点
    						matrix.postScale(scale, scale, midPoint.x, midPoint.y);
    					}
    				}
    				break;
    				
    			case MotionEvent.ACTION_UP:
    				
    				break;
    				//在此前已经有手指按下，屏幕上至少有2根手指
    			case MotionEvent.ACTION_POINTER_DOWN:
    				mode = ZOOM;
    				startDis = distance(event);
    				//距离大于10个像素才处理，防止有手指分叉或有茧；
    				if(startDis > 10f) {
    					midPoint = mid(event);
    					//记录当前的放大倍数
    					currentMatrix.set(imageView.getImageMatrix());
    				}
    				break;
    			case MotionEvent.ACTION_POINTER_UP:
    				mode = 0;
    				break;
    			default:
    				break;
    			} 
    			imageView.setImageMatrix(matrix);
    			//消费掉事件
    			return true;
    		}
    	}
    	
    	//返回2个手指间的距离
    	private static float distance(MotionEvent event) {
    		float dx = event.getX(1) - event.getX(0);
    		float dy = event.getY(1) - event.getY(0);
    		return (float) Math.sqrt(dx*dx+dy*dy);
    	}
    
    	//计算中心点,为2根手指的中心点
    	private static PointF mid(MotionEvent event) {
    		float dx = event.getX(1) + event.getX(0);
    		float dy = event.getY(1) + event.getY(0);
    		return new PointF(dx/2, dy/2);
    	}
    }