Develop Reference

C# WPF add character to textbox without binding

Can i simply add characters without binding this characters to my ViewModel?
I need these to show physical units like cm, mm, m, cm^3, ...
XAML:
<TextBox
Text="{Binding value_top}" //sth. like + "cm"
HorizontalAlignment="Left"
VerticalAlignment="Top"
Width="50"/>
VW:
value_top = 22.9
Output aim:
22.9 cm
I know, I can overlay a Label, but i would like to know if there is another possibility.

Create a converter which will take the double and return a string. Here is an untested example to get you started:
public class DoubleToString: IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var dbl = (double) value;
return $"{dbl} cm";
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return Double.Parse(Regex.Match(value.ToString(), "[\d.]+").Value);
}
}

Binding to last array element

So far, i have an ObservableCollection<T> for objects.
I always want to display the last inserted element into a TextBlock. I implemented two solutions in XAML, but both not working:
<TextBlock Text="{Binding Path=entries.Last().message, FallbackValue=...}" />
<TextBlock Text="{Binding Path=entries[entries.Length-1].message, FallbackValue=...}" />
This one works, but references the first entry:
<TextBlock Text="{Binding Path=entries[0].message, FallbackValue=...}" />
Am i missing something? Is it possible to do with pure XAML?

Solution 1 :
You can use a custom converter to achieve this :
Converter class :
class LastItemConverter : IValueConverter
{
public object Convert(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
IEnumerable<object> items = value as IEnumerable<object>;
if (items != null)
{
return items.LastOrDefault();
}
else return Binding.DoNothing;
}
public object ConvertBack(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new System.NotImplementedException();
}
}
Xaml :
<Application.Resources>
<local:LastItemConverter x:Key="LastItemConverter" />
</Application.Resources>
<TextBlock Text="{Binding Path=entries, Converter={StaticResource LastItemConverter}}" />
Solution 2 :
The other way is to create a new property in your model that returns the entry :
public Object LastEntry => entries.LastOrDefault();
Xaml :
<TextBlock Text="{Binding Path=LastEntry, ... " />

How to bind 2 textboxes to one property?

I have a propery PhoneNumber and in the UI, I have 2 textboxes, one is the prefix, and the other one is the postfix, how can I bind it to the property? (The property inside the DataContext).
<TextBox Grid.Column="0" MaxLength="3" /> //Prefix
<TextBlock Grid.Column="1" Text="-" />
<TextBox Grid.Column="2" /> //Postfix
The only way I see it work is with code behind using textbox1.Text + textbox2.Text... Is there a better way?
Thanks in advance :)

Just use two more properties in the data context
code is not complied or tested
public string PhoneNumber { get; set; }
public string Prefix
{
get
{
return PhoneNumber.Substring(0, 3);
}
set
{
// replace the first three chars of PhoneNumber
PhoneNumber = value + PhoneNumber.Substring(3);
}
}
public string Postfix
{
get
{
return PhoneNumber.Substring(3);
}
set
{
// replace the chars of starting from index 3 of PhoneNumber
PhoneNumber = PhoneNumber.Substring(0, 3) + value;
}
}

I think uou can use Converter for this purpose, the example going one way can look like this:
In this my Number is a string 000-000000, but you can surely change it.
In XAML:
<Window.Resources>
<conv:PostixConverter x:Key="PostfixConv" xmlns:conv="clr-namespace:Example.Converters"/>
<conv:PrefixConverter x:Key="PrefixConv" xmlns:conv="clr-namespace:Example.Converters"/>
</Window.Resources>
<StackPanel>
<TextBox MaxLength="3" Text="{Binding Number, Converter={StaticResource PrefixConv}}"/>
<TextBlock Text="-" />
<TextBox Text="{Binding Number, Converter={StaticResource PostfixConv}}"/>
</StackPanel>
And in code behind:
namespace Example.Converters
{
public class PrefixConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value == null) return null;
else return ((string)value).Substring(0, 3);
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
public class PostixConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value == null) return null;
else return ((string)value).Substring(4);
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
}

An exception of type 'System.Exception' using a converter XAML

I am using a IValueConverter in XAML in my Windows Phone app. My code
<TextBlock Margin="0,0,10,0"
Text="{Binding Score, Converter={StaticResource SecondsToMinutesHour}}"
Foreground="{Binding DeviceID, Converter={StaticResource FontForegroundConverter}}"
FontWeight="{Binding DeviceID, Converter={StaticResource FontWeightConverter}}"
Grid.Column="3" />
However the Converter raised this error
An exception of type 'System.Exception' occurred in System.Windows.ni.dll and wasn't handled before a managed/native boundary
Score is a type string and my converter class is as follow
public class SecondsToMinutesHour : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
int secs = int.Parse(value.ToString());
TimeSpan ts = TimeSpan.FromSeconds(secs);
return String.Format("{0:D2}:{1:D2}:{2:D2}",
ts.Hours,
ts.Minutes,
ts.Seconds);
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
What am I missing?

I figured it out.. I have to include a reference of the SecondsToMinutesHour converter in the Application.Resources section
....
<Application.Resources>
<settings:AppSettings x:Key="AppSettings" />
<app:SecondsToMinutesHour x:Key="SecondsToMinutesHour" />
....

How to pass a static value to IValueConverter in XAML

I would like to use static texts fetched from a web service in my WP7 app. Each text has a Name (the indetifier) and a Content property.
For example a text could look like this:
Name = "M43";
Content = "This is the text to be shown";
I would then like to pass the Name (i.e. the identifier) of the text to an IValueConverter, which would then look up the the Name and return the text.
I figured the converter to look something like this:
public class StaticTextConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value != null)
{
return App.StaticTexts.Items.SingleOrDefault(t => t.Name.Equals(value)).Content;
}
return null;
}
}
Then in the XAML:
<phone:PhoneApplicationPage.Resources>
<Helpers:StaticTextConverter x:Name="StaticTextConverter" />
</phone:PhoneApplicationPage.Resources>
...
<TextBlock Text="{Binding 'M43', Converter={StaticResource StaticTextConverter}}"/>
However, this does not seem to work and I am not sure that I pass in the value to the converter correctly.
Does anyone have some suggestions?

I finally found the answer. The answer was a mix between that of #Shawn Kendrot and another question I asked here: IValueConverter not getting invoked in some scenarios
To summarize the solution for using the IValueConverter I have to bind my control in the following manor:
<phone:PhoneApplicationPage.Resources>
<Helpers:StaticTextConverter x:Name="TextConverter" />
</phone:PhoneApplicationPage.Resources>
<TextBlock Text="{Binding Converter={StaticResource TextConverter}, ConverterParameter=M62}" />
Since the ID of the text is passed in with the converter parameter, the converter looks almost the same:
public class StaticTextConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (parameter != null && parameter is string)
{
return App.StaticTexts.Items.SingleOrDefault(t => t.Name.Equals(parameter)).Content;
}
return null;
}
}
However, as it turns out, the binding and thus the converter is not invoked if it does not have a DataContext. To solve this, the DataContext property of the control just has to be set to something arbitrary:
<TextBlock DataContext="arbitrary"
Text="{Binding Converter={StaticResource TextConverter}, ConverterParameter=M62}" />
And then everything works as intended!

The problem lies in your binding. It will check the DataContext, and on this object, it will try to evaluate the properties M62 and ValueboxConsent on that object.
You might want to add static keys somewhere in your application where you can bind to:
<TextBlock Text="{Binding Source="{x:Static M62.ValueboxConsent}", Converter={StaticResource StaticTextConverter}}" />
Where M62 is a static class where your keys are located.. like so:
public static class M62
{
public static string ValueboxConsent
{
get { return "myValueBoxConsentKey"; }
}
}

If you want to use a value converter, you'll need to pass the string to the parameter of value converter
Xaml:
<TextBlock Text="{Binding Converter={StaticResource StaticTextConverter}, ConverterParameter=M43}"/>
Converter:
public class StaticTextConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (parameter != null)
{
return App.StaticTexts.Items.SingleOrDefault(t => t.Name.Equals(parameter)).Content;
}
return null;
}
}

xmlns:prop="clr-namespace:MyProj.Properties;assembly=namespace:MyProj"
<TextBlock Text="{Binding Source={x:Static prop:Resources.MyString}, Converter={StaticResource StringToUpperCaseConverter}}" />