Android Compose 实现输入4位自动添加空格或横杠

// Making XXXX-XXXX-XXXX-XXXX string.

class TextSpaceVisualTransformation : VisualTransformation {
    override fun filter(text: AnnotatedString): TransformedText {
        val trimmed = if (text.text.length >= 16) text.text.substring(0..15) else text.text
        var out = ""
        for (i in trimmed.indices) {
            out += trimmed[i]
            if (i % 4 == 3 && i != 15) out += "-" //此处换空格
        }

        val numberOffsetTranslator = object : OffsetMapping {
            override fun originalToTransformed(offset: Int): Int {
                if (offset <= 3) return offset
                if (offset <= 7) return offset + 1
                if (offset <= 11) return offset + 2
                if (offset <= 16) return offset + 3
                return 19
            }
            override fun transformedToOriginal(offset: Int): Int {
                if (offset <= 4) return offset
                if (offset <= 9) return offset - 1
                if (offset <= 14) return offset - 2
                if (offset <= 19) return offset - 3
                return 16
            }
        }
        return TransformedText(
            AnnotatedString(out),
            numberOffsetTranslator
        )
    }
}

使用

BasicTextField(
value=""
.
.
visualTransformation =  TextSpaceVisualTransformation(),

)