设置文字的 Alpha 值

AlphaForegroundColorSpan.java

public class AlphaForegroundColorSpan extends ForegroundColorSpan {

    private float mAlpha;

    public AlphaForegroundColorSpan(int color) {
        super(color);
        }
        […]

        @Override
        public void updateDrawState(TextPaint ds) {
                ds.setColor(getAlphaColor());
        }

    public void setAlpha(float alpha) {
        mAlpha = alpha;
    }

    public float getAlpha() {
        return mAlpha;
    }

    private int getAlphaColor() {
        int foregroundColor = getForegroundColor();
        return Color.argb((int) (mAlpha * 255), Color.red(foregroundColor), Color.green(foregroundColor), Color.blue(foregroundColor));
    }
}