Android TextView前增加红色必填项星号*的示例代码

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="NecessaryTextView">
        <attr name="necessary" format="boolean" />
    </declare-styleable>
</resources>

import android.content.Context
import android.graphics.Color
import android.text.Spannable
import android.text.SpannableString
import android.text.style.ForegroundColorSpan
import android.util.AttributeSet
import androidx.appcompat.widget.AppCompatTextView
// TextView that start with a red char of *
class NecessaryTextView : AppCompatTextView {
    private var necessary = false
    constructor(context: Context, attrs: AttributeSet?) : super(context, attrs) {
        val typedArray = context.obtainStyledAttributes(attrs, R.styleable.NecessaryTextView)
        necessary = typedArray.getBoolean(R.styleable.NecessaryTextView_necessary, false)
        typedArray.recycle()
        setText(text, null)
    }
    override fun setText(text: CharSequence?, type: BufferType?) {
        if (necessary) {
            val span = SpannableString("*$text")
            span.setSpan(ForegroundColorSpan(Color.RED), 0, 1, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE)
            super.setText(span, type)
        } else {
            super.setText(text, type)
        }
    }
}