Flutter条件语句未按预期执行：API返回匹配值却进入else分支

我有一段Flutter代码，其中的条件语句未按预期执行，代码如下：

onPressed: () async {
  if ((_formKey.currentState != null && _formKey.currentState!.validate()) ||
      (_formKey1.currentState != null && _formKey1.currentState!.validate())) {
    
    String apiResponse = await loginAPI(email, password);
    print("api response is: $apiResponse");

    if (apiResponse == 'false') {
      setState(() {
        isError = true;
        isErroremail = false;
        print("isError variable is set to true");
      });
    } else if (apiResponse == 'username false') {
      setState(() {
        isErroremail = true;
        isError = false;
        print("isErroremail variable is set to true");
      });
    } else {
      setState(() {
        isError = false;
        isErroremail = false;
        print("isError and isErroremail variables are reset.");
      });
    }

    if (!isError && !isErroremail) {
      ScaffoldMessenger.of(context).showSnackBar(
        const SnackBar(content: Text("processing Data")),
      );
    }
  }
  print("button has been pressed");
},

尽管API返回内容为flutter: api response is: "username false"，但代码并未进入else if (apiResponse == 'username false')分支，打印日志验证如下：

flutter: api response is: "username false"
flutter: isError and isErroremail variables are reset.
flutter: button has been pressed

问题原因 #

API返回的字符串包含首尾双引号（实际值为"username false"），但判断条件是和不带双引号的'username false'做全等比较，两者不匹配，因此代码直接走到else分支。

解决方法 #

方法一：去除API返回字符串的首尾双引号

在获取API响应后，先处理字符串移除多余引号，兼容性更强：

String apiResponse = await loginAPI(email, password);
// 精准去除首尾的双引号
apiResponse = apiResponse.trim();
if (apiResponse.startsWith('"') && apiResponse.endsWith('"')) {
  apiResponse = apiResponse.substring(1, apiResponse.length - 1);
}
print("api response is: $apiResponse");

方法二：修改判断条件匹配带引号的字符串

直接将判断条件中的字符串改为带双引号的形式：

else if (apiResponse == '"username false"') {
  setState(() {
    isErroremail = true;
    isError = false;
    print("isErroremail variable is set to true");
  });
}

内容的提问来源于stack exchange，提问作者Zak345