<Slider Maximum="{Binding ElementName=flowControl, Path=Items.Count}" />
I need to return a Items.Count - 1 for the slider's maximum. How do I define this in xaml?
Many Thanks,
I think in this case you have to use a Value Converter.
e.g.
public class MaxCountConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return (int)value - 1;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
You will probably need to do error handling and stuff and this is just give you a start point.
Use a converter that substracts the 1.
Related
This is an "extension" question to the 1/1/0001 question:
Original Question
The original Q. Solution -
To set the DateTime field to be nullable (DateTime?) solves this problem.
What is the solution when the underlying field must be NOT NULL ?
(In that case, the binding cause the DataGrid column Date Time Picker to set it's self to 01/01/0001)
The Actual Entity in my case is generate by Entity Framework 6.
correct me if I am wrong. You fill your not-null-field with 01/01/0001 to indicate that it's null. (not recommended)
One solution is to define a converter. something like this :
public class NotNullDateConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
var aDateTime = value as DateTime;
if (aDateTime != null && aDateTime == .... )
return null
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
Then you can define a static field to a converter to use it later in xaml.
public static NotNullDateConverter NotNullDateConverter = new NotNullDateConverter();
Then you use this convert inside your xaml for binding:
SelectedDate="{Binding Path=DueDate, Converter={x:Static local:SomeClass.NotNullDateConverter}}"
I had the exact same problem, so I wrote a converter that could weed out non-dates.
//Just weeds out non-dates. Format should be set with StringFormat on the binding
public class DateConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
DateTime date = (DateTime)value;
if (date != null && date.Year != 1)
{
return date;
}
return null;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
I use it like so:
<DataTemplate.Resources>
<logic:DateConverter x:Key="DateConverter"/>
</DataTemplate.Resources>
<TextBlock Text="{Binding LastUpdateTime, StringFormat={}{0:MM/dd/yyyy H:mm:ss}, Converter={StaticResource DateConverter}}"/>
If i use an IValueConverter it works, while with an IMultiValueConverter returning the same value it does not, why is that?
<Border Background="Red" Width="100" Height="100"
CornerRadius="{Binding Converter={vc:SingleAndMultiConverter}}" />
<Border Background="Red" Width="100" Height="100"
CornerRadius="{MultiBinding Converter={vc:SingleAndMultiConverter}}" />
public class SingleAndMultiConverter : MarkupExtension, IValueConverter, IMultiValueConverter
{
public override object ProvideValue(IServiceProvider serviceProvider)
{
return this;
}
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return Convert();
}
public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return Convert();
}
private object Convert()
{
return 15;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotSupportedException();
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotSupportedException();
}
}
The multi-binding throws this error:
Value produced by BindingExpression is not valid for target property.; Value='15'
Border.CornerRadius is of type CornerRadius. Value converters should always return the right type for the property.
It is hard to tell why they behave differently, presumably there is no default value conversion using type converters when using a multi-binding for some unexplained reason. If you were to dig into the source code you might find something but it probably won't be a pleasant journey.
What H.B. said +1
[ValueConversion(typeof(object[]),typeof(CornerRadius))]
public class Multi : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
return new CornerRadius(Double.Parse("15"));
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
I use to bind a bool variable of a class to a IsChecked property of Checkbox. What i want to do is to bind 'NOT' of the original value, like IsChecked = Binding Not(IsSelected), please let me know how this can be done.
Thanks
You need to use a Convertor. A convertor class implements IValueConverter and can convert the binding value into something else, in your case, negate it. You can do it like this:
public class BoolInverseConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value is bool)
return !(bool)value;
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
I want to convert a System.Windows.Media.Color value to a System.Windows.Media.Brush. The color value is databound to a Rectangle object's Fill property. The Fill property takes a Brush object, so I need an IValueConverter object to perform the conversion.
Is there a built-in converter in WPF or do I need to create my own? How do I go about creating my own if it becomes necessary?
I know I am really late to the party, but you don't need a converter for this.
You could do
<Rectangle>
<Rectangle.Fill>
<SolidColorBrush Color="{Binding YourColorProperty}" />
</Rectangle.Fill>
</Rectangle>
It seems that you have to create your own converter. Here a simple example to start:
public class ColorToSolidColorBrushValueConverter : IValueConverter {
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
if (null == value) {
return null;
}
// For a more sophisticated converter, check also the targetType and react accordingly..
if (value is Color) {
Color color = (Color)value;
return new SolidColorBrush(color);
}
// You can support here more source types if you wish
// For the example I throw an exception
Type type = value.GetType();
throw new InvalidOperationException("Unsupported type ["+type.Name+"]");
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
// If necessary, here you can convert back. Check if which brush it is (if its one),
// get its Color-value and return it.
throw new NotImplementedException();
}
}
To use it, declare it in the resource-section.
<local:ColorToSolidColorBrushValueConverter x:Key="ColorToSolidColorBrush_ValueConverter"/>
And the use it in the binding as a static resource:
Fill="{Binding Path=xyz,Converter={StaticResource ColorToSolidColorBrush_ValueConverter}}"
I have not tested it. Make a comment if its not working.
A Converter is not needed here. You can define a Brush in XAML and use it. It would be better to define the Brush as a Resource so it can be used other places required.
XAML is as below:
<Window.Resources>
<SolidColorBrush Color="{Binding ColorProperty}" x:Key="ColorBrush" />
</Window.Resources>
<Rectangle Width="200" Height="200" Fill="{StaticResource ColorBrush}" />
I wanted to do this HCL's way rather than Jens' way because I have a lot of things bound to the Color, so there's less duplication and boiler-plate .Fill nodes.
However when trying to write it, ReSharper pointed me to the WPF Toolkit's implementation of the ColorToSolidColorBrushConverter. You need to include the following namespace declaration in the main Window/UserControl node:
xmlns:Toolkit="clr-namespace:Microsoft.Windows.Controls.Core.Converters;assembly=WPFToolkit.Extended"
Then a static resource in the Window/UserControl resources:
<Toolkit:ColorToSolidColorBrushConverter x:Key="colorToSolidColorBrushConverter" />
Then you can do it like HCL's answer:
<Rectangle Fill="{Binding Color, Converter={StaticResource colorToSolidColorBrushConverter}}" />
With some more enhancment to HCL answer, I tested it - it works.
public class ColorToSolidColorBrushValueConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value == null)
return null;
if (value is Color)
return new SolidColorBrush((Color)value);
throw new InvalidOperationException("Unsupported type [" + value.GetType().Name + "], ColorToSolidColorBrushValueConverter.Convert()");
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value == null)
return null;
if (value is SolidColorBrush)
return ((SolidColorBrush)value).Color;
throw new InvalidOperationException("Unsupported type [" + value.GetType().Name + "], ColorToSolidColorBrushValueConverter.ConvertBack()");
}
}
Converter:
[ValueConversion(typeof(SolidColorBrush), typeof(Color))]
public class SolidBrushToColorConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (!(value is SolidColorBrush)) return null;
var result = (SolidColorBrush)value;
return result.Color;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
XAML:
//...
<converters:SolidBrushToColorConverter x:Key="SolidToColorConverter" />
//...
<Color>
<Binding Source="{StaticResource YourSolidColorBrush}"
Converter="{StaticResource SolidToColorConverter}">
</Binding>
</Color>
//...
In addition to HCLs answer: If you don't want to care if System.Windows.Media.Color is used or System.Drawing.Color you can use this converter, which accepts both:
public class ColorToSolidColorBrushValueConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
switch (value)
{
case null:
return null;
case System.Windows.Media.Color color:
return new SolidColorBrush(color);
case System.Drawing.Color sdColor:
return new SolidColorBrush(System.Windows.Media.Color.FromArgb(sdColor.A, sdColor.R, sdColor.G, sdColor.B));
}
Type type = value.GetType();
throw new InvalidOperationException("Unsupported type [" + type.Name + "]");
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
Using Pattern matching there's no need for neither null checking and double casting:
public class ColorToSolidBrushValueConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value is Color color) return new SolidColorBrush(color);
throw new InvalidOperationException(nameof(color));
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) => new NotImplementedException();
}
Optional implementation for ConvertBack:
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value is SolidColorBrush brush)
{
return brush.Color;
}
throw new InvalidOperationException(nameof(brush));
}
Is there any way so that i can show only first character of a Bound string on a textblock..?
For eg;If i Bind 'Male', my textblock should only show 'M'.....
You might use a value converter to return a string prefix:
class PrefixValueConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
string s = value.ToString();
int prefixLength;
if (!int.TryParse(parameter.ToString(), out prefixLength) ||
s.Length <= prefixLength)
{
return s;
}
return s.Substring(0, prefixLength);
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotSupportedException();
}
}
And in XAML:
<Window.Resources>
...
<local:PrefixValueConverter x:Key="PrefixValueConverter"/>
</Window.Resources>
...
...{Binding Path=TheProperty, Converter={StaticResource PrefixValueConverter},
ConverterParameter=1}...