CODEWITHSUNDEEP
c#mvvmxamarin.forms
krcarbo
krcarbo

Reputation: 25

How to work with a model in viewModel

I'm having a problem with using MVVM for a Xamarin project.

I can not refresh the user interface if one of my objects in my viewModel is updated (after a PUT request, for example).

Let me explain :

My model : 

public class MyObject
{
    public string Id { get; private set; }
    public string Name { get; private set; }
}

My viewmodel : 

public class MyViewModel : BaseViewModel
{
    public MyObject MyObject { get; private set; }

    public string IdMvvm
    {
        set
        {
            if (this.MyObject.Id != value)
            {
                MyObject.Id = value;
                OnPropertyChanged(nameof(IdMvvm));
            }
        }
        get { return MyObject.Id; }
    }

    public string NameMvvm
    {
        set
        {
            if (this.MyObject.Name != value)
            {
                MyObject.Name = value;
                OnPropertyChanged(nameof(NameMvvm));
            }
        }
        get { return MyObject.Name; }
    }
}

BaseViewModel implements INotifyPropertyChanged

public class BaseViewModel : INotifyPropertyChanged
{
    public string PageTitle { get; protected set; }
    LayoutViewModel() {}

    // MVVM ----------------------------------------------------------------------------------------
    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    protected void SetValue<T>(ref T backingField, T value, [CallerMemberName] string propertyName = null)
    {
        if (EqualityComparer<T>.Default.Equals(backingField, value))
            return;

        backingField = value;

        OnPropertyChanged(propertyName);
    }

MyViewModel is defined as BindingContext for my page My properties IdMvvm and NameMvvm are bind in Entry in my page in xaml

When I modify an Entry then the value is raised but if my MyModel object changes value, for example update (click on a button) then the value of the different Entry is not updated

Can you help me please? Because it seems that I missed something ... If you need more explanation, tell me to know

Sorry if my english is not good

Upvotes: 0

Views: 85

Answers (1)

Dipen Shah
Dipen Shah

Reputation: 26095

It is because when you change the model, your view is not aware about the change. Update your code so that you explicitly notify property changes when your model changes.

public class MyViewModel : BaseViewModel
{
    private MyObject _myObject;
    public MyObject MyObject 
    { 
       get { return _myObject; }
       private set { _myObject = value; NotifyModelChange(); }
    }

    public string IdMvvm
    {
        set
        {
            if (this.MyObject.Id != value)
            {
                MyObject.Id = value;
                OnPropertyChanged(nameof(IdMvvm));
            }
        }
        get { return MyObject.Id; }
    }

    public string NameMvvm
    {
        set
        {
            if (this.MyObject.Name != value)
            {
                MyObject.Name = value;
                OnPropertyChanged(nameof(NameMvvm));
            }
        }
        get { return MyObject.Name; }
    }

    private void NotifyModelChange()
    {
         OnPropertyChanged(nameof(IdMvvm));
         OnPropertyChanged(nameof(NameMvvm));
    }
}

Upvotes: 1

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