根據圖片的寬高和ImageView的寬高，實現圖片不壓縮、不裁剪顯示圖片。

自定義控制元件繼承ImageView,在onDraw中計算圖片和控制元件的寬高比，按最小的寬高比進行縮放。

 @Override
    protected void onDraw(Canvas canvas) {
        Drawable drawable = getDrawable();

        if (drawable == null) {
            return;
        }


        if (getWidth() == 0 || getHeight() == 0) {
            return;
        }
        this.measure(0, 0);

        if (drawable.getClass() == NinePatchDrawable.class) {
            return;
        } else if (drawable instanceof AsyncDrawable) {
            return;
        }
        Bitmap b = ((BitmapDrawable) drawable).getBitmap();

        Bitmap bitmap = b.copy(Bitmap.Config.ARGB_8888, true);

        if (bitmap.getWidth() == 0 || bitmap.getHeight() == 0) {

            return;
        }


        if (defaultWidth == 0) {
            defaultWidth = getWidth();

        }

        if (defaultHeight == 0) {
            defaultHeight = getHeight();

        }

        float scaleHeght = (float) defaultHeight / (float) bitmap.getHeight();
        float scaleWight = (float) defaultWidth / (float) bitmap.getWidth();
        if (scaleHeght >= scaleWight) {
            scale = scaleWight;
        } else {
            scale = scaleHeght;
        }
//        scale = (float) defaultHeight / (float) bitmap.getHeight();

        defaultWidth = Math.round(bitmap.getWidth() * scale);
        defaultHeight = Math.round(bitmap.getHeight() * scale);

        LayoutParams params = this.getLayoutParams();

        params.width = defaultWidth;

        params.height = defaultHeight;

        this.setLayoutParams(params);


        super.onDraw(canvas);


    }