Android图片处理总结四:双击图片,保持点击位置不变放大

双击ImageView，需要保持图片点击点相对布局的位置不变，然后放大图片，因为项目大量的ImageView都需要这个功能，所以扩展了ImageView。主要是：

1.扩展ImageView类

2.重写手势控制类GestureDetector.SimpleOnGestureListener 中的onDoubleTap()方法

3.利用Matrix进行放大和平移图片

详细代码如下，有详细注释：

//扩展ImageView类
public class ScaleImageView extends ImageView{
private Drawable nullDrawable;
//定义手势控制类
private GestureDetectorCompat mDetector;
private float initX,initY;
private Matrix matrix;
private float defaultScale = 1.0f;
private float preScaleX = 1.0f,preScaleY = 1.0f;
public LocalImageView(Context context) {
super(context);
}

public ScaleImageView (Context context, AttributeSet attrs) {
super(context, attrs);
init(context, attrs);
}

public ScaleImageView (Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init(context, attrs);
}

private void init(Context context, AttributeSet attrs)
{
nullDrawable = null;
if(attrs != null) {
TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.ImageStyle);

nullDrawable = typedArray.getDrawable(R.styleable.ImageStyle_nullDrawable);
typedArray.recycle();

}
mDetector = new GestureDetectorCompat(context, new MyGestureListener());
matrix = new Matrix();
}

@Override
protected void onFinishInflate() {
super.onFinishInflate();
}

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
if(nullDrawable != null)
nullDrawable.setBounds((getWidth() - nullDrawable.getIntrinsicWidth())/2,(getHeight() - nullDrawable.getMinimumHeight())/2,(getWidth() - nullDrawable.getIntrinsicWidth())/2+ nullDrawable.getIntrinsicWidth(),(getHeight() - nullDrawable.getMinimumHeight())/2 + nullDrawable.getMinimumHeight());
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}

@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
}

@Override
protected void onDraw(Canvas canvas) {
if(this.getDrawable() == null) {
canvas.drawColor(getResources().getColor(R.color.clr_grey));
if (nullDrawable != null)
nullDrawable.draw(canvas);
}
super.onDraw(canvas);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();
//使用手势控制类处理MotionEvent
mDetector.onTouchEvent(event);
return true;
}
//扩展GestureDetector.SimpleOnGestureListener类
class MyGestureListener extends GestureDetector.SimpleOnGestureListener {
//重写onDoubleTap方法
@Override
public boolean onDoubleTap(MotionEvent e) {
//获取双击坐标
float clickX = e.getX();
float clickY = e.getY();

//H获取上一次的方法系数
float oldScale = getScale();
//每次双击放大倍数加0.1
float scale = oldScale + 0.1f;

//获取上一次的平移量,
float oldTranX = -getTranX();
float oldTranY = -getTranY();

//设置放大系数
matrix.setScale(scale,scale);

/*
计算新的平移量：
1.算出点击点相对于目前图片的坐标:
clickX和clickY是点击坐标，相对于图片(已经被放大)的坐标需要加上平移量clickX + oldTranX
2.算出点击点相对于原图片的坐标(注意是原始图片)：
(clickX + oldTranX)/oldScale
3.算出此次放大，点击点相对于放大图片的坐标(注意是放大后的图片)：
((clickX + oldTranX)/oldScale)*scale
4..计算新的平移量：
((clickX + oldTranX)/oldScale)*scale - clickX
*/
float tranX  = -(((clickX - oldTranX)/oldScale)*scale - clickX);
float tranY  = -(((clickY - oldTranY)/oldScale)*scale - clickY);
//设置平移,因为是要向左和向上平移，所以是负数
matrix.postTranslate(-tranX,-tranY);
//设置矩阵
setImageMatrix(matrix);
return super.onDoubleTap(e);
}
}
public float getScale()
{
float[] values = new float[9];
matrix.getValues(values);
return values[Matrix.MSCALE_X];
}

public float getTranX()
{
float[] values = new float[9];
matrix.getValues(values);
return values[Matrix.MTRANS_X];
}

public float getTranY()
{
float[] values = new float[9];
matrix.getValues(values);
return values[Matrix.MTRANS_Y];
}