SpannableString添加ImageSpan居中处理

Android图文混排可以通过SpannableString来实现，但是imageSpan只提供了两种对齐方式：ALIGN_BOTTOM，ALIGN_BASELINE两种方式，并没有居中对齐方式。

自定义ImageSpan

public class CenterImageSpan extends ImageSpan {

    public CenterImageSpan(Drawable drawable) {
        super(drawable);

    }

    public CenterImageSpan(Bitmap bitmap) {
        super(bitmap);
    }

    @Override
    public void draw(@NonNull Canvas canvas, CharSequence text, int start, int end, float x, int top, int y, int bottom,
            @NonNull Paint paint) {

        Drawable b = getDrawable();
        Paint.FontMetricsInt fm = paint.getFontMetricsInt();
        int transY = (y + fm.descent + y + fm.ascent) / 2 - b.getBounds().bottom / 2;//计算y方向的位移
        canvas.save();
        canvas.translate(x, transY);//绘制图片位移一段距离
        b.draw(canvas);
        canvas.restore();
    }
}

使用方式

 
  if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
  			   //创建SpannableString对象
               val sp = SpannableString("Test String")
             
  				//拿到所加图片的drawable对象
                val drawable =context.getDrawable(R.drawable.iv_to_add)
                drawable.setBounds(0, 0, drawable.minimumWidth, drawable.minimumHeight)
				
				//给SpannableString设置ImageSpan
                val imageSpan = CenterImageSpan(drawable)
                sp.setSpan(imageSpan, sp.length - 1, sp.length, ImageSpan.ALIGN_BASELINE)
    
    			textview.text=sp
     }