WPF ListView与ObservableCollection的绑定问题

Question

I have a ListView which binds to an ObservableCollection named GunsCollection

<Grid>
<ListView x:Name="lstView" Height="300" ItemsSource="{Binding GunsCollection}">
    <ListView.View>
        <GridView>
            <GridViewColumn Header="Gun Name" Width="120" DisplayMemberBinding="{Binding ModelName}"/>
            <GridViewColumn Header="Price" Width="120" DisplayMemberBinding="{Binding UnitCost}"/>
        </GridView>
    </ListView.View>
</ListView>

When I create the instance of GunsCollection in the constructor of MainWindow , my ListView doesn't show anything and is empty.

public partial class MainWindow : Window
{
    public ObservableCollection<Gun> GunsCollection { get; set; } 
    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = this;
        var GunsCollection = new ObservableCollection<Gun>() // doesn't work!
        {
            new Gun() {ModelName = "AK-47", UnitCost = 2700 },
            new Gun() {ModelName = "M4A4", UnitCost = 3100 },
        };
    }
}

But when I create the instance of GunsCollection on the same line with its declaration, the ListView works and shows all of the items contained.

public partial class MainWindow : Window
{
    public ObservableCollection<Gun> GunsCollection { get; set; } = new ObservableCollection<Gun>(); 
    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = this;
        GunsCollection.Add(new Gun() { ModelName = "AK-47", UnitCost = 2700 });
        GunsCollection.Add(new Gun() { ModelName = "M4A4", UnitCost = 3100 });
    }
}

Why is this happening?

Answer 1

In your first example the GunsCollection you fill with data will no longer exist after the constructor has been executed. You've created a new variable which has nothing to do with your class property (even if it has the same name).

Answer 2

The first example you display, you create a new local variable and don't assign it to your public collection which is bound to your view.

public partial class MainWindow : Window
{
    public ObservableCollection<Gun> GunsCollection { get; set; } 
    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = this;
        GunsCollection = new ObservableCollection<Gun>() 
        {
            new Gun() {ModelName = "AK-47", UnitCost = 2700 },
            new Gun() {ModelName = "M4A4", UnitCost = 3100 },
        };
    }
}

Remove var