前几天做项目用到相机拍照，之后能对图片进行缩放，拖拽，在此我将其单独抽取出来，后面用到时直接拿来用就行了！
效果图：
注：这里不仅能按钮缩放，还能多点触摸缩放和拖拽功能！
1.布局：
2.就一个类：
import android.app.Activity;import android.content.Intent;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.Matrix;import android.graphics.PointF;import android.os.Bundle;import android.util.FloatMath;import android.util.Log;import android.view.MotionEvent;import android.view.View;import android.view.View.OnClickListener;import android.view.View.OnTouchListener;import android.widget.Button;import android.widget.FrameLayout;import android.widget.ImageView;import android.widget.LinearLayout;/** * 缩放图片界面 * @author ZHF * */public class MainActivity extends Activity { public static final String TAG = "ImgDisplayActivity"; //控件声明 private Button btnZoomin, btnZoomout; private ImageView imgDisPlay; private LinearLayout lLayoutDisplay; private FrameLayout fLayoutDisplay; private Bitmap bitmap; private int imgId = 0; private double scale_in = 0.8;//缩小比例 private double scale_out = 1.25;//放大比例 private float scaleWidth = 1; private float scaleHeight = 1; //模式：0：什么都不干；1：拖拽； 2：缩放 public static final int NONE = 0; public static final int DRAG = 1; public static final int ZOOM = 2; //声明触发的事件模式 private int mode = NONE; private Matrix matrix; //矩阵 private Matrix currMatrix; //当前矩阵 private PointF starPoint; private PointF midPoint; private float startDistance; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); //初始化 fLayoutDisplay = (FrameLayout) findViewById(R.id.flayout_img_display); lLayoutDisplay = (LinearLayout) findViewById(R.id.linearLayout_img_display); imgDisPlay = (ImageView) findViewById(R.id.img_display); btnZoomin = (Button) findViewById(R.id.btn_min); btnZoomout = (Button) findViewById(R.id.btn_out); matrix = new Matrix(); //保存拖拽变化 currMatrix = new Matrix();// 当前的 starPoint = new PointF();//开始点的位置 btnZoomin.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { zoomIn(); } }); btnZoomout.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { zoomOut();//放大 } }); imgDisPlay.setImageResource(R.drawable.img); //给图片绑定监听器哦 imgDisPlay.setOnTouchListener(new ImageViewOnTouchListener()); } /**放大操作**/ private void zoomOut() { reSizeBmp(scale_out); btnZoomin.setEnabled(true); } /**缩小操作**/ private void zoomIn() { reSizeBmp(scale_in); } /**接收传入的缩放比例实现缩放**/ private void reSizeBmp(double scale) { //缩放比例 scaleWidth = (float) (scaleWidth * scale); scaleHeight = (float) (scaleHeight * scale); Matrix matrix = new Matrix(); matrix.postScale(scaleWidth, scaleHeight); //设计缩放比例 imgDisPlay.setImageMatrix(matrix); } /**计算触摸实现缩放**/ final class ImageViewOnTouchListener implements OnTouchListener{ @Override public boolean onTouch(View v, MotionEvent event) { switch (event.getAction() & MotionEvent.ACTION_MASK) { case MotionEvent.ACTION_DOWN: //一只手指按下 Log.i(TAG,"一只手指按下"); currMatrix.set(matrix); starPoint.set(event.getX(), event.getY()); mode = DRAG; break; case MotionEvent.ACTION_POINTER_DOWN: //如果有一只手指按下屏幕，后续又有一个手指按下 // 两只手指按下 Log.i(TAG,"又有一只手指按下"); startDistance = distance(event);//记下两点的距离 Log.i(TAG, startDistance+""); if(startDistance > 5f) { //两个手指之间的最小距离像素大于5，认为是多点触摸 mode = ZOOM; currMatrix.set(matrix); midPoint = getMidPoint(event); //记下两个点之间的中心点 } break; case MotionEvent.ACTION_MOVE: if(mode == DRAG) { //拖拽模式 Log.i(TAG,"一只手指在拖拽"); //开始--》结束点的距离 float dx = event.getX() - starPoint.x; float dy = event.getY() - starPoint.y; matrix.set(currMatrix); matrix.postTranslate(dx, dy);//移动到指定点：矩阵移动比例；eg:缩放有缩放比例 } else if(mode == ZOOM) { //缩放模式 Log.i(TAG,"正在缩放"); float distance = distance(event); //两点之间的距离 if(distance > 5f) { matrix.set(currMatrix); float cale = distance / startDistance; matrix.preScale(cale, cale, midPoint.x, midPoint.y); //进行比例缩放 } } break; case MotionEvent.ACTION_UP: //最后一只手指离开屏幕后触发此事件 case MotionEvent.ACTION_POINTER_UP: //一只手指离开屏幕，但还有一只手指在上面会触此事件 //什么都没做 mode = NONE; break; default: break; } imgDisPlay.setImageMatrix(matrix); //两只手指的缩放 return true; } } /**计算两点之间的距离像素**/ private float distance(MotionEvent e) { float eX = e.getX(1) - e.getX(0); //后面的点坐标 - 前面点的坐标 float eY = e.getY(1) - e.getY(0); return FloatMath.sqrt(eX * eX + eY * eY); } /**计算两点之间的中心点**/ private 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); }}
ok！主要的算法就在ImageViewOnTouchListener监听器当中，要考虑那三种情况（缩放、拖拽、什么都不干），另外需要注意的就是，单个手指和两个以上手指的情况。
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