如何实现Imageview图片进行缩放

几个重要知识点：

1、布局文件中android:scaleType=”matrix” 设置图片动态缩放

2、matrix.postTranslate(dx,dy); 平移图片 matrix.postScale(sx,sy,p.x,p.y); 缩放图片

3、两点的中点、距离计算方式，限制缩放范围函数，在指定区域内移动图片方法

(以下代码网上很多地方有类似的，仅供参考)

public class Main extends Activity

{

private static final int NONE = 0;

private static final int DRAG = 1;

private static final int ZOOM = 2;

private int mode = NONE;
private float oldDist;
private Matrix matrix = new Matrix();
private Matrix savedMatrix = new Matrix();
private PointF start = new PointF();
private PointF mid = new PointF();

ImageView view;
Bitmap bitmap;
DisplayMetrics dm;
float minScaleR=0.1f;  //最少缩放比例
static final float MAX_SCALE = 4f; //最大缩放比例
float dist = 1f;

@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
view = (ImageView) findViewById(R.id.image_view);
bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.test);

dm = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(dm); //获取分辨率

matrix.setScale(minScaleR, minScaleR); //开始先缩小
matrix.postTranslate(120, 120);     //图片的位置相对于imageview的左上角往右往下各偏移120个像素
view.setImageMatrix(matrix);

view.setOnTouchListener(new OnTouchListener()
{
@Override
public boolean onTouch(View v, MotionEvent event)
{
ImageView view = (ImageView) v;
switch (event.getAction() & MotionEvent.ACTION_MASK)
{
case MotionEvent.ACTION_DOWN:  //单点
Toast.makeText(Main.this, bitmap.getWidth()+"*"+bitmap.getHeight(), Toast.LENGTH_LONG).show();
savedMatrix.set(matrix);
start.set(event.getX(), event.getY());
mode = DRAG;
break;
case MotionEvent.ACTION_UP:  //单点弹起
case MotionEvent.ACTION_POINTER_UP:  //多点弹起
mode = NONE;
break;
case MotionEvent.ACTION_POINTER_DOWN:  //多点
oldDist = spacing(event);
if (oldDist > 10f)
{
savedMatrix.set(matrix);
midPoint(mid, event);
mode = ZOOM;
}
break;
case MotionEvent.ACTION_MOVE: //按下且在拖动
if (mode == DRAG)
{
matrix.set(savedMatrix);
matrix.postTranslate(event.getX() - start.x,event.getY() - start.y);  //xy方向都可以拖动
//matrix.postTranslate(event.getX() - start.x,0); //只在x轴方向拖动 即左右拖动  上下不动
//matrix.postTranslate(0,event.getY() - start.y);  //只在y轴方向拖动 即上下拖动  左右不动
}
else if (mode == ZOOM)
{
float newDist = spacing(event);
if (newDist > 10f)
{
matrix.set(savedMatrix);
float scale = newDist / oldDist;
matrix.postScale(scale, scale, mid.x, mid.y);
}
}
break;
}

view.setImageMatrix(matrix);

CheckScale();  //限制缩放范围
center();  //居中控制

return true;
}

//两点的距离
private float spacing(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);
}

//两点的中点
private void midPoint(PointF point, MotionEvent event)
{
float x = event.getX(0) + event.getX(1);
float y = event.getY(0) + event.getY(1);
point.set(x / 2, y / 2);
}
});
}

//限制最大最小缩放比例
protected void CheckScale()
{
float p[] = new float[9];
matrix.getValues(p);
if (mode == ZOOM)
{
if (p[0] < minScaleR)
{
matrix.setScale(minScaleR, minScaleR);
}
if (p[0] > MAX_SCALE)
{
matrix.set(savedMatrix);
}
}
}

//自动居中  左右及上下都居中
protected void center()
{
center(true,true);
}

private void center(boolean horizontal, boolean vertical)
{
Matrix m = new Matrix();
m.set(matrix);
RectF rect = new RectF(0, 0, bitmap.getWidth(), bitmap.getHeight());
m.mapRect(rect);
float height = rect.height();
float width = rect.width();
float deltaX = 0, deltaY = 0;
if (vertical)
{
//int screenHeight = dm.heightPixels;  //手机屏幕分辨率的高度
int screenHeight = 400;
if (height < screenHeight)
{
deltaY = (screenHeight - height)/2 - rect.top;
}else if (rect.top > 0)
{
deltaY = -rect.top;
}else if (rect.bottom < screenHeight)
{
deltaY = view.getHeight() - rect.bottom;
}
}

if (horizontal)
{
//int screenWidth = dm.widthPixels;  //手机屏幕分辨率的宽度
int screenWidth = 400;
if (width < screenWidth)
{
deltaX = (screenWidth - width)/2 - rect.left;
}else if (rect.left > 0)
{
deltaX = -rect.left;
}else if (rect.right < screenWidth)
{
deltaX = screenWidth - rect.right;
}
}
matrix.postTranslate(deltaX, deltaY);
}

}