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;

@Override
protected 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