flutter - value.isEmpty 在我尝试编译代码时抛出错误

Question

 TextFormField(
                        obscureText: true,
                        decoration: InputDecoration(
                          hintText: "Enter password",
                          labelText: "Password",
                        ),
                        validator: (value) {
                          if (value.isEmpty) {
                            return "Password can't be empty";
                          }
                          null;
                        },
                      ),

我正在看一个关于颤振的教程，我知道它太基础了，但似乎无法修复这个错误但不适合我，我还不明白它显示The property 'isEmpty' can't be unconditionally accessed because the receiver can be 'null'. Try making the access conditional (using '?.') or adding a null check to the target ('!'). 这个错误

标签： flutterdart

Answer 1

这是因为valueis 类型String?并且可以为 null。在你的情况下，你必须检查 if valueis null。

 TextFormField(
                        obscureText: true,
                        decoration: InputDecoration(
                          hintText: "Enter password",
                          labelText: "Password",
                        ),
                        validator: (String? value) {
                          if (value!.isEmpty) {
                            return "Password can't be empty";
                          }
                          null;
                        },
                      ),