How to avoid zoomed ImageView from being dragged out of the screen?

Question

I have an ImageView whose Drawable can be zoomed in or out. The Drawable can be dragged inside the ImageView, but it can be dragged out of the screen so that for example the left border of the Drawable may be place at the center of the screen. I tried the solution given by Benito Bertoli and it works perfectly for the initial image which is not zoomed. How can I use this solution when the image is zoomed?

Answer 1

I do this:

if (event.getAction()==MotionEvent.ACTION_POINTER_UP || event.getAction()==MotionEvent.ACTION_UP) {
        float[] matrixValues=new float[9];
        matrix.getValues(matrixValues);
        PointF coordenadas = validatePosition(matrixValues);
        if (coordenadas.x!=0 || coordenadas.y!=0){
            matrix.postTranslate(coordenadas.x,coordenadas.y);
            //view is a imageView
            view.setImageMatrix(matrix);
        }
}

and this is the methods:

private PointF validatePosition(float[] matrixValues){
    SizeF pantalla=getDisplaySize();
    SizeF zoomed=getImagenZoomSize(matrixValues[Matrix.MSCALE_X],matrixValues[Matrix.MSCALE_Y]);
    //System.out.println("M_TRANS: "+matrixValues[Matrix.M TRANS_X]+","+matrixValues[Matrix.M TRANS_Y]+"  Pantalla:"+pantalla.getWidth()+","+pantalla.getHeight()+"   Imagen:"+zoomed.getWidth()+","+zoomed.getHeight());
    PointF respuesta=new PointF(0,0);
    respuesta.set(calculateAbsolutePosition(matrixValues[Matrix.MTRANS_X],zoomed.getWidth(),pantalla.getWidth()),respuesta.y);
    respuesta.set(respuesta.x,calculateAbsolutePosition(matrixValues[Matrix.MTRANS_Y],zoomed.getHeight(),pantalla.getHeight()));
    return respuesta;
}

private SizeF getDisplaySize(){
    Point dimension=new Point();
    Display display=getWindowManager().getDefaultDisplay();
    display.getSize(dimension);
    pantalla=new SizeF(dimension.x,dimension.y);
    return pantalla;
}

private SizeF getImagenZoomSize(float scaleX, float scaleY){
    SizeF original=getOriginalImageSize();
    return new SizeF(original.getWidth()*scaleX,original.getHeight()*scaleY);
}

private float calculateAbsolutePosition(float actual, float medidaImagen, float medidaPantalla){
    float max, min;
    float desplazamiento;
    if (medidaPantalla>medidaImagen){
        max=(medidaPantalla-medidaImagen)/2;
        min=max;
    }
    else{
        max=0;
        min=medidaPantalla-medidaImagen;
    }
    if (actual<min){
        desplazamiento=-actual+min;
    }
    else if (actual>max){
        desplazamiento=-actual+max;
    }
    else{ //no movemos la imagen (desplazamiento=0)
        desplazamiento=0;
    }
    return desplazamiento;
}