Set value to null in WPF binding - wpf

please take a look at the following line
<TextBox Text="{Binding Price}"/>
This Price property from above is a Decimal? (Nullable decimal).
I want that if user deletes the content of the textbox (i.e. enters empty string, it should automatcally update source with null (Nothing in VB).
Any ideas on how I can do it 'Xamly'?

I am using .NET 3.5 SP1 so it's very simple:
<TextBox Text="{Binding Price, TargetNullValue=''}"/>
Which stands for (thanks Gregor for your comment):
<TextBox Text="{Binding Price, TargetNullValue={x:Static sys:String.Empty}}"/>
sys is the imported xml namespace for System in mscorlib:
xmlns:sys="clr-namespace:System;assembly=mscorlib"
Hope that helped.

This value converter should do the trick :
public class StringToNullableDecimalConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter,
CultureInfo culture)
{
decimal? d = (decimal?)value;
if (d.HasValue)
return d.Value.ToString(culture);
else
return String.Empty;
}
public object ConvertBack(object value, Type targetType,
object parameter, CultureInfo culture)
{
string s = (string)value;
if (String.IsNullOrEmpty(s))
return null;
else
return (decimal?)decimal.Parse(s, culture);
}
}
Declare an instance of this converter in the ressources :
<Window.Resources>
<local:StringToNullableDecimalConverter x:Key="nullDecimalConv"/>
</Window.Resources>
And use it in your binding :
<TextBox Text="{Binding Price, Converter={StaticResource nullDecimalConv}}"/>
Note that TargetNullValue is not appropriate here : it is used to define which value should be used when the source of the binding is null. Here Price is not the source, it's a property of the source...

You can try using a ValueConverter (IValueConverter)
http://msdn.microsoft.com/en-us/library/system.windows.data.ivalueconverter.aspx
Of the back of my head here, something like:
public class DoubleConverter : IValueConverter
{
public object Convert(object value, Type targetType,
object parameter, CultureInfo culture)
{
return (double)value;
}
public object ConvertBack(object value, Type targetType,
object parameter, CultureInfo culture)
{
var doubleValue = Convert.ToDouble(value);
return (doubleValue == 0 ? null : doubleValue);
}
}
(Might need some tweaking though)

Related

xaml Binding to enum. Display value instead of "ToString"

I have a property of an enum type. I bind the content of a wpf control to this property. This will display the name of the enum value. So the ToString Method of enum is called.
But I need to display the value, not the string value. Does anyone know how to do this?
This is my C# code:
public enum Animal
{
cat = 0,
dog = 1,
mouse = 2
}
public Animal MyAnimal { get; set; }
void SomeMethod() { MyAnimal = dog; }
This is in my XAML:
<Label Content="{Binding MyAnimal}">
When you bind to a value of one type and want to display it in another format than the default ToString() method provides you should either use a DataTemplate or an IValueConverter. Since XAML is a markup language you cannot really cast the enumeration value to an int in your markup so you should use a converter:
public class EnumConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
animals enumValue = (animals)value;
return System.Convert.ToInt32(enumValue);
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
<Window.Resources>
<local:EnumConverter x:Key="conv" />
</Window.Resources>
...
<ContentControl Content="{Binding TheEnumProperty, Converter={StaticResource conv}}" />
I have found a solution:
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (!(value is Enum)) return value;
return Enum.IsDefined(value.GetType(), value) ? value : System.Convert.ToInt32(value);
}

How to use specific properties of a Value converter in wpf xaml

I have a enum to string converter
public class EnumToStringConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter,
CultureInfo culture)
{
MailSettingsStateEnum enumValue = (MailSettingsStateEnum)value;
// extension method on the enum, to return a string based on enum.
return enumValue.Description();
}
// ConvertBack not relevant here.
}
I am using this in wpf xaml easily as follows to set the Content property of a label.
<Label Content="{Binding MailSettingState, Converter={StaticResource
EnumConverterString}}"
BorderBrush="{Binding MailSettingState, Converter={StaticResource
EnumConverterBorderBrush}}" />
Now as you can see, I have another property BorderBrush. I also have to set this based on the same enum. And so I had to write another converter EnumConverterBorderBrush
So is there a way by which I have only one converter, and it return an object which has two properties and i can use these properties in the xaml? I can create the converter, its easy, but I dont know how to use it in xaml. Say the converter returned an object and has tow property called MessageString(of type string), and another BorderBrush of the type Brush, how do I use it the xaml?
You can switch the output based on the targetType you receive in your converter.
So you could do something like this:
public class EnumToStringConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter,
CultureInfo culture)
{
var enumValue = (MailSettingsStateEnum)value;
switch(targetType)
{
case typeof(string)
return enumValue.Description();
case typeof(Brush)
return enumValue.GetBrush();
default:
throw new NotSupportedException("Type not supported")
}
}
// ConvertBack not relevant here.
}
Now you'll have one converter to rule them all!
converter should return object which match requested targetType. converter can return different values for input enum value depending on parameter. I think it is more flexible than relying on targetType only.
public class SpecEnumConverter: IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value is Enum)
{
if ((string) parameter == "brush")
return "Red"; // return brush here!
// if not pre-defined parameter (null or any other), return description
return (int) value; // return enum description here!
}
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
usage:
<Label Content="{Binding MailSettingState, Converter={StaticResource
EnumConverterSpec}}"
BorderBrush="{Binding MailSettingState, Converter={StaticResource
EnumConverterSpec}, ConverterParameter='brush'}" />
I already commented above, but here's the solution.
<Label DataContext="{Binding MailSettingState, Converter={converters:EnumConverter}}" Content="{Binding Label}" BorderBrush="{Binding BorderBrush}"/>
public class EnumConverter: MarkupExtension, IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var enumValue = (MailSettingsStateEnum) value;
return new ConvertedEnum { Label = enumValue.Description(),
BorderBrush = new BorderBrush()};
}
// ConvertBack not relevant here.
public override object ProvideValue(IServiceProvider serviceProvider)
{
return this;
}
}
public class ConvertedEnum
{
public string Label {get; set;}
public BorderBrush {get; set;}
}
Separate converters still look prettier to me.

DatePicker databinding sets default value to 1/1/0001 WPF c# for a Not-Nullable date

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}}"/>

textbox visibility/collapsed in silverlight mvvm

I Silverlight5 with mvvm pattern i have one doubt.
In xaml i have used one textblock and i bind some id in it.
If the textblock content value is 1 or 2 means
yet another textbox is visible or else that is collapsed.. how to acheive that..
my code:
<TextBlock Name="textBlock1" Text="{Binding id}" Loaded="textBlock1_Loaded" Visibility="Collapsed" />
<TextBox Text="{Binding name,Mode=TwoWay}" x:Name="t1" Visibility="{Binding IsVisible,Converter={StaticResource visibilityconverter}}" />
in view model i had created the property for id and raised the event and bind the value to textblock.
to convert the value to visible i have a visibilityconverter class in one separate folder named "Converters"
public class visibilityconverter:IValueConverter
{
public object Convert(object value, Type targetType,
object parameter, CultureInfo culture)
{
if (id==1 && id==2)
{
return Visibility.Visible;
}
return Visibility.Collapsed;
}
public object ConvertBack(object value, Type targetType,
object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
in the above visibleconverter class how i cna get the id value from viewmodel and check it..
If i got the value from viewmodel to visibilityconverter means i will proceed further.
tell me if u can..!
Hi i have found the solution..
In xaml give the following:
<TextBox Text="{Binding name,Mode=TwoWay}" x:Name="t1" Visibility="{Binding id,Converter={StaticResource visibilityconverter}}" />
In visibilityConverter class:
public class visibilityconverter:IValueConverter
{
public object Convert(object value, Type targetType,
object parameter, CultureInfo culture)
{
string v = value.ToString();
if (v =="1" || v=="2")
{
return Visibility.Visible;
}
return Visibility.Collapsed;
}
public object ConvertBack(object value, Type targetType,
object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
Problem Solved... !

WPF Ivalueconverter empty values

I use a Ivalueconverter to convert a string to a boolean using an xml datasource. This works fine until I manually change the xml like so:
myelement.InnerXml = "true"
I then receive a formatexception saying the string is not a valid boolean, I check the value that goes in to my converter and it is equal to ""
Here is my converter:
[ValueConversion(typeof(string), typeof(bool))]
public class StringToBoolConverter : IValueConverter {
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
return TypeDescriptor.GetConverter(typeof(bool)).ConvertFrom(value); }
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
return value.ToString();
}
}
I bind the converter like so:
<local:StringToBoolConverter x:Key="stringbool"></local:StringToBoolConverter>
And apply it in the binding:
IsChecked="{Binding Mode=TwoWay, UpdateSourceTrigger=PropertyChanged, XPath=myelement, Converter={StaticResource stringbool}}"
I'm not sure, but if you use "XPath=myelement", the string should be
myCheckBox.DataContext="<myelement>true</myelement>";

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