How do I change the background color of a textblock in MVVM-WPF

Question

I am new to WPF technology. i am using MVVM architecture. I want to change the background of textblock based on viewmodel's attribute. e.g If i am using 'brush' object, I want to bind it to background color of textblock.

<TextBlock Margin="0,1"
                    HorizontalAlignment="Center"
                    FontFamily="Arial"
                    FontSize="16"
                    Text="{Binding Line}"
                    TextWrapping="Wrap"
                    Background="{Binding brushobj}"/>

How to implement it?

eandersson · Accepted Answer · 2011-12-05 19:06:30Z

2

You could define it like this, inside your ViewModel.

private Brush _brushobj;
/// <summary>
/// Gets or sets the BrushObject.
/// </summary>
public Brush BrushObj
{
    get
    {
        return _brushobj;
    }
    set
    {

        // Set value
        _brushobj = value;

        // Notify UI that the value has changed.
        RaisePropertyChanged("BrushObj");
        // OnPropertyChanged("BrushObj"); // Use the appropriate function to notify the UI.
    }
}

Then simply set the value with something like this:

BrushObj = (Brush)new BrushConverter().ConvertFromString("Green");

Last you bind it to your View like you did in your question:

Background="{Binding BrushObj}"

Edit: I tried to make a project myself just to verify that this was indeed working and the following code worked fine. If it's still not working it's more likely to be something with your MVVM setup causing problem.

MainWindowViewModel:

namespace WpfApplication1
{
        public class MainWindowViewModel : ObservableObject
        {
           private Brush _brushobj = (Brush)new BrushConverter().ConvertFromString("Red");
           public Brush BrushObj
           {
                get
                {
                     return _brushobj;
                }
                set
                {
                     _brushobj = value; // Set value
                     RaisePropertyChanged("BrushObj"); // Notify UI that the value has changed.
                }
           }
      }
}

MainWindow:

    <Window x:Class="WpfApplication1.MainWindow"
            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
            Title="MainWindow" Height="350" Width="525">
        <Grid>
            <TextBlock Margin="0,1"
                        VerticalAlignment="Center"
                        HorizontalAlignment="Center"
                        FontFamily="Arial"
                        FontSize="16"
                        Text="Testing a lot of stuff here! important stuff!"
                        TextWrapping="Wrap"
                        Background="{Binding BrushObj}"/>
        </Grid>
    </Window>

edited Dec 5, 2011 at 19:06

answered Dec 5, 2011 at 8:28

eandersson

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13 Comments

deathrace Over a year ago

Thanks, I tried the same. But its still not working. Background color haven't changed yet.

eandersson Over a year ago

Make sure that you have INotifyPropertyChanged implemented properly in your ViewModel if it isn't updating. You could also try to add UpdateSourceTrigger=PropertyChanged to your XAML code. Background="{Binding BrushObj, UpdateSourceTrigger=PropertyChanged}"

deathrace Over a year ago

should I have to uncomment //OnPropertyChanged("BrushObj") event?

eandersson Over a year ago

It depends on how you implement INotifyPropertyChanged. If the first code compiled without problems it should be fine, depends on what framework and such you use for MVVM; like for example PRISM or MVVM Light.

eandersson Over a year ago

If you are having problems, feel free to post some additional code from your ViewModel and I'll take a look. :)

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