WPF
===

# MVVM

## ViewModel:
* Doesn't need reference to a view.
* The bindings between view and ViewModel are simple to construct, because a ViewModel object is set as the DataContext of a view.
* The bindings between view and ViewModel is reactive.
* Works on Event-EventHandler architecture.
* ViewModels perform any and all mutations on the model data

### DataContext
* Mechanism for allowing elements to inherit info from thier parent elements.

#### DataContext in xaml file

1. Import all the name spaces
* ` xmlns:<namespace>` declares a namespace

<!-- MainWindow.xaml -->
<Window
     
    xmlns:views="clr-namespace:<Views Namespace>"
    xmlns:viewModels="clr-namespace:<ViewModel Namespace>"
    ...
    ...
>

2. Define ViewModel Resource and alias it
* `<Element.Resource>` defines resources for the element.
* `x:Key="ViewModelAlias"` defines alias for ViewModel

        <Element.Resource>
            <viewModels:ViewModel x:Key="ViewModelAlias"/>
        </Element.Resource>

3. Bind ViewModel Resource to the element DataContext

        <Element.DataContext>
            <Binding Source="{ StaticResource ViewModelAlias }"/>
        </Element.DataContext>

4. Binding Resource attributes to child element

        <ChildElement Value="{ Binding ViewModelAttribute }">

__Note__ Window element is the root element and all subsequent elements would be contained in the `Element` tag.

### `ObservableCollection<T> _V`

* can be used as a XAML object element in WPF.
* Must be a `private readonly` attribute
* Exposed by `public IEnumerable<T> V => _V ` which is exposed to the View Template via the DataContext.

## View

### Templates and Styling

* Global Styles are specified in the `App.xml` file.

<!-- App.xml -->
<Application.Resources>
    <Style TargetType="<TargetElementName>">
        <Setter Property="<PropertyName>" Value="<PropertyName>">
        ...
        <Setter Property="<AnotherPropertyName>" Value="<AnotherPropertyName>">
    </Style>
</Application.Resources>

* Defining a list view using a ListBox element

<!-- ListView.xaml -->
    <Element.Resources>
        ...
        <DataTemplate x:Key="<ListItemTemplate>">
            <!-- StackPanel is a layout Element -->
            <StackPanel>
                <TextBlock Text="{ Binding <ItemSourceAttribute> }">
            </StackPanel>
        </DataTemplate>
    </Element.Resources>
...
    <!-- ItemSource = ObservableCollection<T> -->
    <ListBox ItemsSource="{Binding <ListOfItems>}" ItemTemplate="{StaticResource <ListItemTemplate>}"

### Commands
* Basically mutators (actions),

###### tags: c# csharp mvvm wpf