WPF binding to variable in different class

Question

Hey guys I have the following issue,

I'm trying to bind a variable to a listbox to show a list of strings. This should change automatically when a new item is added to the list so I used an ObservableCollection. However I can't seem to bind the variable to the Listbox.

GroupPage.xaml.cs:

private readonly GroupController groupController;
private Group group;

public GroupPage(GroupController groupController)
{
    InitializeComponent();
    this.groupController = groupController;
    LoadData();
}

private void LoadData()
{
    group = groupController.GetGroup();
    LblGroupName.Content = group.Name;
}

private void BtnDetails_OnClick(object sender, RoutedEventArgs e)
{
    throw new NotImplementedException();
}

private void btnSend_Click(object sender, RoutedEventArgs e)
{
    string message = "[Chat] " + group.GroupId + " " + DataLayer.Instance.CurrentLoggedInUser.FirstName + " " + tbChat.Text;
    MainController.Instance.SendToServer(message);
}

Group.cs:

public int GroupId { get; set; }

public string Name { get; set; }

public string InterestId { get; set; }

public DateTime Creation { get; set; }

public string Description { get; set; }

public ObservableCollection<string> Chat { get; set; } = new ObservableCollection<string>();

public Group()
{

}

public Group(string name, string description, string interestId)
{
    Name = name;
    Description = description;
    InterestId = interestId;
}

public Group(MySqlDataReader reader)
{
    GroupId = reader.GetInt32("group_id");
    Name = reader.GetString("group_name");
    Description = reader.GetString("group_description");
    Creation = reader.GetDateTime("creation_date");
}

GroupPage.xaml

<Page x:Class="TeamRockstarPlatform.View.GroupPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:TeamRockstarPlatform.View"
    mc:Ignorable="d" d:DesignHeight="1080" d:DesignWidth="1920"
    Title="Group Page">
<Grid>
    <Rectangle Fill="#FFFFE000" Height="86" VerticalAlignment="Top" Width="Auto" HorizontalAlignment="Stretch"/>
    <Rectangle Fill="#FF232323" Height="86" VerticalAlignment="Top" Width="28" HorizontalAlignment="Left"/>
    <Ellipse x:Name="ImgGroup" Fill="White" HorizontalAlignment="Left" Height="125" Margin="125,24,0,0" Stroke="#FF232323" VerticalAlignment="Top" Width="125" StrokeThickness="3"/>
    <Label x:Name="LblGroupName" Content="Management" HorizontalAlignment="Left" Margin="255,51,0,0" VerticalAlignment="Top" FontSize="24" FontFamily="Microsoft Sans Serif"/>

    <Button x:Name="BtnDetails" Content="Details" Click="BtnDetails_OnClick" HorizontalAlignment="Right" Margin="0,102,1563,0" VerticalAlignment="Top" Width="102" Background="#FFFFE000" BorderBrush="{x:Null}" Foreground="White" FontFamily="Microsoft Sans Serif" FontSize="20" Height="35"/>


    <Grid x:Name="Chat" Margin="0,150,0,0">


    </Grid>
    <Grid x:Name="Details" Margin="0,150,0,0">
        <Grid>
            <!-- BASIC INFO -->
            <TextBox x:Name="TbxGroupName" MaxLength="50" HorizontalAlignment="Left" Height="35" Margin="257,20,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="519" FontFamily="Microsoft Sans Serif" FontSize="22" BorderBrush="Black"/>
            <RichTextBox x:Name="TbxDescription" HorizontalAlignment="Left" Height="146" Margin="257,71,0,0" VerticalAlignment="Top" Width="519" FontFamily="Microsoft Sans Serif" FontSize="22" BorderBrush="Black"/>
            <Button x:Name="BtnSave" Content="Save" HorizontalAlignment="Left" Margin="257,244,0,0" VerticalAlignment="Top" Width="103" Background="#FFFFE000" BorderBrush="{x:Null}" Foreground="White" FontFamily="Microsoft Sans Serif" FontSize="20" Height="35"/>
            <Label Content="Name: " HorizontalAlignment="Left" Margin="145,20,0,0" VerticalAlignment="Top" FontFamily="Microsoft Sans Serif" FontSize="22"/>
            <Label Content="Description: " HorizontalAlignment="Left" Margin="94,71,0,0" VerticalAlignment="Top" FontFamily="Microsoft Sans Serif" FontSize="22"/>

            <Button x:Name="btnSend" Content="Send" HorizontalAlignment="Left" VerticalAlignment="Top" Width="287" Margin="257,508,0,0" Height="38" Click="btnSend_Click"/>
            <TextBox x:Name="tbChat" HorizontalAlignment="Left" Height="23" Margin="257,480,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="287"/>
            <ListBox HorizontalAlignment="Left" Height="171" Margin="257,304,0,0" VerticalAlignment="Top" Width="287"/>
        </Grid>
    </Grid>

</Grid>

So I'm trying to bind the Chat property from Group to this Listbox.

Further to mm8's answer, once group is your DataContext, you should be binding LblGroupName.Content as well: <Label Content="{Binding Name, FallbackValue=Management}" />, rather than assigning it in codebehind. — 15ee8f99-57ff-4f92-890c-b56153
– 15ee8f99-57ff-4f92-890c-b56153, Commented May 16, 2018 at 14:09

mm8 · Accepted Answer · 2018-05-16 14:04:55Z

3

If you set the DataContext of the Page to an instance of your Group class:

public GroupPage(GroupController groupController)
{
    InitializeComponent();
    this.groupController = groupController;
    LoadData();
    DataContext = group;
}

...you should be able to bind to any property of it:

<ListBox ... ItemsSource="{Binding Chat}" />

answered May 16, 2018 at 14:04

mm8

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