Maui Mvvm working with Observable Property Class Model, how to call a class object correctly in a method - mvvm

Question

Still pretty new to maui and mvvm, I'm trying to figure out of to access elements in a observable property class in a method. For example I have a login class like below:
public class LoginModel
{
public string Failmessage { get; set; } = string.Empty;
public string Username { get; set; } = string.Empty;
public string Password { get; set; } = string.Empty;
public bool Validusername { get; set; } = true;
public bool Vaildpassword { get; set; } = true;
}
In my modelview I call the observable property LoginModel loginModel
[ObservableProperty]
LoginModel LoginModel
public LoginPageViewModel()
{
LoginModel login= new();
}
I want to check the property value in a method like below but it keeps giving me errors. like Fields with [ObservableProperty] should not be directly referenced, and the generated properties should be used instead.
if ((string.IsNullOrEmpty(LoginModel.Username)) || (string.IsNullOrWhiteSpace(LoginModel.Username)))
{
IsBusy = false;
LoginModel.Validusername = false;
return;
}
Am I doing something wrong here?
I want to be able to access the element of the class in a method.

Answer 1

From your code, I found that you should have used nuget CommunityToolkit.Mvvm.
And the problem is that you didn't use CommunityToolkit.Mvvm correctly.
You can try to add prefix partial before class LoginPageViewModel and declare loginmodel starting with small letter,thenLoginmodel property will be generated for you by MVVM Toolkit.
You can refer to the following code:
public partial class LoginPageViewModel:ObservableObject
{
[ObservableProperty]
LoginModel loginmodel;
public LoginPageViewModel() {
//LoginModel login = new();
Loginmodel = new LoginModel();
}
public void Test() {
if ((string.IsNullOrEmpty(Loginmodel.Username)) || (string.IsNullOrWhiteSpace(Loginmodel.Username)))
{
//IsBusy = false;
Loginmodel.Validusername = false;
return;
}
}
}
Update
now the if statement is working but when I set
Loginmodel.Validusername = false; the view is not updating with this
new value.
If you want the UI update automatically once changing the value of model Loginmodel, you also need to implement interface INotifyPropertyChanged for class LoginModel.
Please refer to the following code:
public class LoginModel: INotifyPropertyChanged
{
public string Failmessage { get; set; } = string.Empty;
public string Username { get; set; } = string.Empty;
public string Password { get; set; } = string.Empty;
// public bool Validusername { get; set; } = true;
// modify code as follows
private bool _validusername;
public bool Validusername
{
get => _validusername;
set
{
SetProperty(ref _validusername, value);
}
}
public bool Vaildpassword { get; set; } = true;
bool SetProperty<T>(ref T storage, T value, [CallerMemberName] string propertyName = null)
{
if (Object.Equals(storage, value))
return false;
storage = value;
OnPropertyChanged(propertyName);
return true;
}
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
public event PropertyChangedEventHandler PropertyChanged;
}

Answer 2

ViewModels are ObservableObjects, not ObservableProperties.
They contain ObservableProperties.
Do not construct manually your ViewModels. Use dependency injection and register them as services.
For this what you call "check property value", that are actually ObservableProperties in ObservableObject, there is ObservableValidator class.
https://learn.microsoft.com/en-us/dotnet/communitytoolkit/mvvm/observablevalidator
Fix this, and ask if you have any questions.