图片缩放

package bawei.com.myapplication;

import android.graphics.Matrix;
import android.graphics.PointF;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {
private ImageView picture;
private float xl;
private float yl;
private final int MODE_DRAG = 1;
private final int MODE_ZOOM = 2;
private final int MODE_NONE = 0;
private int currentMode = MODE_NONE;
private double distanceStart;

@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    initView();}Matrix matrix = new Matrix();Matrix matrixNew = new Matrix();private void initView() {    picture = (ImageView) findViewById(R.id.picture);    picture.setOnTouchListener(new View.OnTouchListener() {        @Override        public boolean onTouch(View v, MotionEvent event) {            switch (event.getAction() & MotionEvent.ACTION_MASK) {                case MotionEvent.ACTION_DOWN:                    currentMode = MODE_DRAG;                    xl = event.getX();                    yl = event.getY();                    matrix.set(picture.getImageMatrix());                    break;                case MotionEvent.ACTION_POINTER_DOWN:                    //计算两个手指间的距离                    distanceStart = spacing(event);                    if (distanceStart > 20) {                        currentMode = MODE_ZOOM;                        matrix.set(picture.getImageMatrix());                    }                    break;                case MotionEvent.ACTION_MOVE:                    if (currentMode == MODE_DRAG) {                        matrixNew.set(matrix);                        float xn = event.getX();                        float yn = event.getY();                        //matrix.setTranslate(xn,yn);                        matrixNew.postTranslate(xn - xl, yn - yl);                    } else if (currentMode == MODE_ZOOM) {                        if (spacing(event) > 20) {                            matrixNew.set(matrix);                            double distance = spacing(event);                            float scale = (float) (distance / distanceStart);                            PointF pointF = myPointF(event);                            matrixNew.postScale(scale, scale, pointF.x, pointF.y);                        }                    }                    break;                case MotionEvent.ACTION_UP:                    currentMode = MODE_NONE;                    break;            }            picture.setImageMatrix(matrixNew);            return true;        }    });}//计算两点之间的距离private double spacing(MotionEvent event) {    float x = 0;    float y = 0;    try {        x = event.getX(0) - event.getX(1);        y = event.getY(0) - event.getY(1);    } catch (IllegalArgumentException e) {}    return Math.sqrt(x * x + y * y);}public PointF myPointF(MotionEvent event){    float x1 = event.getX(0);    float x2 = event.getX(1);    float y1 = event.getY(0);    float y2 = event.getY(1);    float x = (x1+x2)/2;    float y = (y1+y2)/2;    PointF pointF = new PointF(x, y);    return pointF;}

}

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xml布局