WPF Discussion Boards

MemberDotNetting6-May-12 3:41

6-May-12 3:41

i try to change the size of text in ritchbox with code behind

TextRange tr = new TextRange(rtb.Document.ContentStart, rtb.Document.ContentEnd);
tr.ApplyPropertyValue(FontSizeProperty, (double)9);

but i want to change

tr.ApplyPropertyValue(FontSizeProperty, (double)9)

double size=Convert.ToDouble(comboboxfontsize.selectedItem)// or selected value;
tr.ApplyPropertyValue(FontSizeProperty, size)

i get an exception

Impossible d'effectuer un cast d'un objet de type 'System.Windows.Controls.ComboBoxItem' en type 'System.IConvertible'.

so how can i get the value selected item?

Re: WPF RichTextBox

Wayne Gaylard6-May-12 21:07

Wayne Gaylard

6-May-12 21:07

I don't know how you are populating the ComboBox, but I assume it is in the XAML. In this case the SelectedItem would be a ComboBoxItem which does not implement the IConvertible interface and so cannot be converted to a double. Personally, I would use WPF's binding mechanism to implement this using 2 properties, and ObservableCollection<int> to hold the allowed font sizes, and an int property to hold the selected font size, something like this:-

public ObservableCollection<int> Fonts
{
get
{
    return new ObservableCollection<int>() { 8, 9, 10, 12, 14 };
}
}

int selectedFontSize;
public int SelectedFontSize
{
get
{
    return selectedFontSize;
}
set
{
    if (selectedFontSize != value)
    {
        selectedFontSize = value;
        OnPropertyChanged("SelectedFontSize");
    }
}
}

(this assumes you user control / window implements INotifyPropertyChanged). Then you can just create the bindings in your XAML like this:

XML

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto"/>
        <RowDefinition />
    </Grid.RowDefinitions>
    <ComboBox ItemsSource="{Binding Fonts}" SelectedItem="{Binding SelectedFontSize}" Width="200" HorizontalAlignment="Left"/>
    <RichTextBox Grid.Row="1">
        <FlowDocument FontSize="{Binding SelectedFontSize}">
            <Paragraph >
                Hello World!
            </Paragraph>
        </FlowDocument>
    </RichTextBox>
</Grid>

and that is all there is to it, not forgetting to set the DataContext of your user control / window to itself like this in the constructor:

public MainWindow()
{
    InitializeComponent();
    this.DataContext = this;
}

Hope this helps

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