SpannableString实现渐变文字

1. 编写LinearGradientFontSpan继承ReplacementSpan

public class LinearGradientFontSpan extends ReplacementSpan {
    private int mSize;
    private int startColor;
    private int endColor;

    public LinearGradientFontSpan(int startColor, int endColor) {
        this.startColor = startColor;
        this.endColor = endColor;
    }

    @Override
    public int getSize(@NonNull Paint paint, CharSequence text, int start, int end, @Nullable Paint.FontMetricsInt fm) {
        mSize = (int) paint.measureText(text , start , end);
        Paint.FontMetricsInt metrics = paint.getFontMetricsInt();
        if (fm != null) {
            fm.top = metrics.top;
            fm.ascent = metrics.ascent;
            fm.descent = metrics.descent;
            fm.bottom = metrics.bottom;
        }
        return mSize;
    }

    @Override
    public void draw(@NonNull Canvas canvas, CharSequence text, int start, int end, float x, int top, int y, int bottom, @NonNull Paint paint) {
        LinearGradient lg = new LinearGradient(0, 0, 0, paint.descent() - paint.ascent(),
                startColor,
                endColor,
                Shader.TileMode.REPEAT); //从上到下渐变
        paint.setShader(lg);
        canvas.drawText(text, start, end, x, y, paint);//绘制文字
    }
}

2. 使用

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView textView = findViewById(R.id.text_view);
        //这里使用刚创建的工具类
        LinearGradientFontSpan linearGradientFontSpan = new LinearGradientFontSpan(Color.RED, Color.BLUE);
        SpannableString spannableString = new SpannableString("hello");
        //第一个参数是格式，第二个参数起始位置，第三个结束位置（但不包括结束位置），,第四个模式，共有四种
        spannableString.setSpan(linearGradientFontSpan , 2 , 5 , Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
        textView.setText(spannableString);//设置spann
    }
}

原文链接：https://blog.csdn.net/csdn_zxw/article/details/108306276