Android:处理 InputFilter 上的退格键

Question

我为 EditText 组件创建了一个 InputFilter，它只允许在一个范围内(例如从 1.5 到 5.5)出现 double 值。一切正常，直到我删除了小数点:

我输入了 1.68，然后删除了小数点。文本域中的值变成了168，明显超出了范围。

这是我的过滤器的简化版本

public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) {
        if (isValid(dest.toString() + source.toString())) {
            //input is valid
            return null;
        }else{
          //The input is not valid
            return "";
        }
}
private boolean isValid(String input) {
    Double inputValue = Double.parseDouble(input);
    boolean isMinValid = (1.5 <= inputValue);
    boolean isMaxValid = (5.5 >= inputValue);

    return  isMinValid && isMaxValid;
}

Answer 1

我解决了我的问题。这是解决方案，以防其他人需要它:

public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) {
    if (isValid(dest.toString() + source.toString())) {
        //input is valid
        return null;
    }else{
      //The input is not valid
       if (source.equals("") && dest.toString().length() != 1) {
            //backspace was clicked, do not accept that change, 
            //unless user is deleting the last char
            CharSequence deletedCharacter = dest.subSequence(dstart, dend);
            return deletedCharacter;
        }
        return "";
    }