WPF TabControl only load the selected TabItem

 public class TabItemViewModel
 {
        public string Header { get; set; }
        public FrameworkElement Content { get; set; }
 }

xmlns:sc="clr-namespace:System.Collections;assembly=mscorlib"
<Window.Resources>
    <sc:ArrayList x:Key="Datas">
        <local:TabItemViewModel Header="uer1">
            <local:TabItemViewModel.Content>
                <local:UserControl1 />
            </local:TabItemViewModel.Content>
        </local:TabItemViewModel>
        <local:TabItemViewModel Header="uer2">
            <local:TabItemViewModel.Content>
                <local:UserControl2 />
            </local:TabItemViewModel.Content>
        </local:TabItemViewModel>
    </sc:ArrayList>
</Window.Resources>

<TabControl ItemsSource="{StaticResource Datas}">
    <TabControl.ItemContainerStyle>
        <Style TargetType="TabItem">
            <Setter Property="Header" Value="{Binding Header}"/>
            <Setter Property="Content" Value="{Binding Content}"/>
        </Style>
    </TabControl.ItemContainerStyle>
</TabControl>

<TabControl SelectionChanged="TabControl_SelectionChanged">
    <TabItem Header="zzu Red"">
        <Grid Background="Red"/>
    </TabItem>
    <TabItem Header="zzu Orange">
        <Grid Background="Orange"/>
    </TabItem>
</TabControl>

private void TabControl_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    TabControl tabControl = sender as TabControl;
    for (int i = 0; i < tabControl.Items.Count; i++)
    {
        TabItem item = tabControl.Items[i] as TabItem;
        if (item.IsSelected)
        {
            if (item.Content == null)
            {
                item.Content = item.Tag;
            }
            else
            {
                item.Tag = item.Content;
            }
        }
        else
        {
            item.Tag = item.Content;
            item.Content = null;
        }
    }
}