ViewModels

The ViewModel is the centre of Aspid.MVVM. The Source Generator emits the binding code for every field marked with an attribute.

Contents

• Creating a ViewModel
• The [Bind] attribute
• Shorthand attributes
• The [BindAlso] attribute
• The [BindId] attribute
• The [Access] attribute
• Change handlers
• MonoViewModel
• ScriptableViewModel
• NotifyAll

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Creating a ViewModel

The smallest ViewModel:

using Aspid.MVVM;

[ViewModel]
public partial class PlayerViewModel
{
    [OneWayBind] private string _name;
    [OneWayBind] private int _health;
}

Requirements:

1. The class is partial: the Source Generator completes it
2. The [ViewModel] attribute marks it for the generator
3. At least one field with a [Bind] attribute

The Source Generator implements IViewModel and emits:

• A property for every marked field
• BindableMember<T> for every binding
• FindBindableMember() for dispatch
• NotifyAll() for bulk notification

Three flavours of ViewModel

Type	Base class	When to use
POCO	None	The default. Plain C# without Unity dependencies
MonoViewModel	MonoBehaviour	When the ViewModel must be editable in the Inspector
ScriptableViewModel	ScriptableObject	Data shared between scenes

---

The [Bind] attribute

Marks a field for binding generation. The mode is detected or set explicitly:

[ViewModel]
public partial class ExampleViewModel
{
    // Automatic mode:
    [Bind] private const string Title = "Hello";  // → OneTime (const)
    [Bind] private readonly int _id;                // → OneTime (readonly)
    [Bind] private string _name;                    // → TwoWay  (mutable)

    // Explicit mode:
    [Bind(BindMode.OneWay)] private int _score;
    [Bind(BindMode.TwoWay)] private string _input;
}

Naming rules

The Source Generator understands the common field naming styles:

Field	Generated property
_outText	OutText
m_outText	OutText
s_outText	OutText
outText	OutText

---

Shorthand attributes

A shorter way to set the mode:

[ViewModel]
public partial class ShortcutExample
{
    [OneWayBind] private string _label;          // BindMode.OneWay
    [TwoWayBind] private float _volume;          // BindMode.TwoWay
    [OneTimeBind] private IRelayCommand _save;   // BindMode.OneTime
    [OneWayToSourceBind] private string _input;  // BindMode.OneWayToSource
}

---

The [BindAlso] attribute

When the field changes, the named property is notified as well. Used for computed properties:

[ViewModel]
public partial class PersonViewModel
{
    [BindAlso(nameof(Nickname))]
    [BindAlso(nameof(FullName))]
    [Bind] private string _name;

    [BindAlso(nameof(FullName))]
    [Bind] private string _family;

    // Computed properties, refreshed when _name or _family changes
    private string Nickname => Name.ToLower();
    private string FullName => $"{Name} {Family}";
}

When Name changes, binders attached to Nickname and FullName are notified too.

---

The [BindId] attribute

Overrides the binding id (by default the generated property name):

[ViewModel]
public partial class CustomIdViewModel
{
    // The _text1 field binds under the id "Text2"
    [BindId("Text2")]
    [Bind] private string _text1;

    // The Do method binds as the command "OtherDoCommand"
    [RelayCommand]
    [BindId("OtherDoCommand")]
    private void Do() { }
}

Useful when the View field name does not match the ViewModel member name.

---

The [Access] attribute

Controls the visibility of the generated property:

[ViewModel]
public partial class AccessExample
{
    // private string Text1 { get; set; }  (default)
    [Bind] private string _text1;

    // public string Text2 { get; set; }
    [Access(Access.Public)]
    [Bind] private string _text2;

    // protected string Text3 { get; set; }
    [Access(Access.Protected)]
    [Bind] private string _text3;

    // public string Text4 { get; private set; }
    [Access(Get = Access.Public)]
    [Bind] private string _text4;

    // public string Text5 { get; protected set; }
    [Access(Get = Access.Public, Set = Access.Protected)]
    [Bind] private string _text5;

    // protected string Text6 { private get; set; }
    [Access(Get = Access.Protected, Set = Access.Public)]
    [Bind] private string _text6;
}

Access levels

• Access.Private: the default for get and set
• Access.Protected: visible to subclasses
• Access.Public: visible to everyone

Get and Set are configured independently, so properties like public get / private set are possible.

---

Change handlers

The Source Generator declares partial methods called when a property changes:

[ViewModel]
public partial class HandlerExample
{
    [Bind] private string _name;

    // Called BEFORE Name changes
    partial void OnNameChanging(string oldValue, string newValue)
    {
        // Validation or logging
    }

    // Called AFTER Name changes
    partial void OnNameChanged(string newValue)
    {
        // Update dependent data
    }
}

Pattern: react to input immediately

[ViewModel]
public partial class MomentSpeakerViewModel
{
    [TwoWayBind] private string _inputText;

    private readonly Speaker _speaker;

    // Every change of the InputField text
    // updates the model at once
    partial void OnInputTextChanged(string newValue)
    {
        _speaker.Say(newValue);
    }
}

---

MonoViewModel

For ViewModels edited in the Inspector:

using UnityEngine;
using Aspid.MVVM;

[ViewModel]
public partial class SettingsViewModel : MonoViewModel
{
    [SerializeField] [OneWayBind] private float _musicVolume = 0.8f;
    [SerializeField] [OneWayBind] private float _sfxVolume = 1.0f;
}

Details:

• Inherits MonoBehaviour
• OnValidate() calls NotifyAll(), so Inspector edits show up immediately
• Dispose() calls Destroy(this)

---

ScriptableViewModel

For ViewModels shared between scenes:

using UnityEngine;
using Aspid.MVVM;

[ViewModel]
public partial class GameConfigViewModel : ScriptableViewModel
{
    [SerializeField] [OneWayBind] private string _gameName;
    [SerializeField] [OneWayBind] private int _maxPlayers;
}

Details:

• Inherits ScriptableObject
• OnValidate() calls NotifyAll()
• Can be created through CreateAssetMenu

---

NotifyAll

A generated method that pushes the current values to every binding:

var viewModel = new PlayerViewModel();
viewModel.Health = 100;
viewModel.Name = "Hero";
viewModel.Armor = 50;

// Notify every binder of the current values at once
viewModel.NotifyAll();

When to use:

• After a bulk update of several fields
• After deserialization / loading data
• In MonoViewModel.OnValidate() (called automatically)

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See also

• Binding Modes, details of BindMode
• Commands, the [RelayCommand] attribute
• Views, creating a View for a ViewModel
• Dynamic ViewModel, a ViewModel without code generation