I'm trying to implement the MVVM design pattern in my WPF application but I have some problems to bind my Views with my ViewModels.
In one of my ViewModels, I have the following property :
public IPEndPoint EndPoint
{
get { return _serverInfos.EndPoint; }
private set
{
_serverInfos.EndPoint = value;
RaisePropertyChanged("EndPoint");
}
}
I want to bind this property in the related View like that :
<TextBox Text="{Binding EndPoint.Address}" />
<TextBox Text="{Binding EndPoint.Port}" />
The EndPoint.Port binding works as expected but the other one doesn't because EndPoint.Address is not a string (it's an IPAddress). Of course, I could define two string properties instead of one IPEndPoint but I think that it's not a good solution.
I also have the same problem using Enums when I want to convert them into int :
<ComboBox SelectedIndex="{Binding MyEnumProperty}" />
How could I solve these problems ?
Thank you for your help.
Normally you want a view model to take things from the model and expose them in a way that the view can consume. As such
MyEnumProperty should be an System.Int32 (int) for ComboBox.SelectedIndex to consumer
You should probably implement two separate properties for EndPointPort and EndPointAddress, and EndPointAddress should be a string that converts to an IPAddress when working with the model
You can use IValueConverters for both of those, but then you are reducing some of the utility of a separate view model in the first place if all it does is act like the model.
A converter you can use for converting between IPAddress and string.
public class IPAddressConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var ipAddress = value as IPAddress;
if (ipAddress != null)
{
return ipAddress.ToString();
}
return DependencyProperty.UnsetValue;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
var text = value as string;
IPAddress ipAddress;
if (text != null && IPAddress.TryParse(text, out ipAddress))
{
return ipAddress;
}
return DependencyProperty.UnsetValue;
}
}
And then in a ResourceDictionary or a Resources collection of a FrameworkElement
<IPAddressConverter x:Key="IpAddressConverter" />
And in the binding:
<TextBox Text="{Binding EndPoint.Address, Converter={StaticResource IpAddressConverter}}" />
As far as the IPEndPoint type, this is a perfect case for a type converter (IValueConverter). It would look something like this, assuming your type has a valid ToString implementation:
public class IPEndPointConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
IPEndPoint endPoint = (IPEndPoint)value;
return endPoint.ToString();
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
You could then add the converter to your XAML file with a ResourceDictionary as follows (assuming you've added the relevant namespace, here called "converters", to your XAML):
<Window.Resources>
<converters:IPEndPointConverter x:Key="ipEndPointConverter" />
</Window.Resources>
You would then simply use this anywhere you need it within your XAML by adding it to the binding:
<TextBox Text="{Binding Path=EndPoint.Address, Converter={StaticResource ResourceKey=ipEndPointConverter}}" />
Related
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.
I have created a class named "BoundProperty" which contains a property "Value".
Binding to a property which is an instance of that class looks this way
(Age is a BoundProperty):
<TextBox Text="{Binding MyModel.Age.Value, Mode=TwoWay}" />
Is there a way to make the binding look this way and additionally still retain it two-way?
<TextBox Text="{Binding MyModel.Age, Mode=TwoWay}" />
I can't use implicit/explicit conversion operators, for this "BoundProperty" initialization requires special parameters, which need to be copied from original object.
Thanks,
AD
If Value is public you can use ValueConverter:
public class BoundPropertyConverter:IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
var age = value as BoundProperty;
if (age == null)
return string.Empty;
return age.Value;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
int age;
if (int.TryParse(value.ToString(), out age))
return new BoundProperty() {Value = age};
return null;
}
}
Then in xaml define namespace to this converter
xmlns:converters="clr-namespace:Your.Namespace"
And then in Resources area write something like this:
<converters:BoundPropertyConverter x:Key="BoundPropertyConverter"/>
And last but not least:
<TextBox Text="{Binding MyModel.Age, Mode=TwoWay, Converter={StaticResource BoundPropertyConverter}" />
I have a bit defined in my database 0=no, 1=yes. I have a silverlight combo with the values "Yes" and "No" in it. How can I bind my bit value to the combo?
You don't state what data access machinary you are using but the typical tools will expose a bit field as a boolean property. The easiest approach would be to use a value converter.
Here is the basic idea (might need some more defensive coding):-
public class BoolToStringConverter : IValueConverter
{
public String FalseString { get; set; }
public String TrueString { get; set; }
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value == null)
return FalseString;
else
return (bool)value ? TrueString : FalseString;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return value.Equals(TrueString);
}
}
With that in your application you can now add it to a Resources property (typically the App.xaml)
<Resources>
<local:BoolToStringConverter x:Key="CvtYesNo" FalseString="No" TrueString="Yes" />
</Resources>
Now you would create your combobox like this:-
<ComboBox SelectedItem="{Binding YourBitField, Converter={StaticResource CvtYesNo}, Mode=TwoWay}">
<sys:String>Yes<sys:String>
<sys:String>No<sys:String>
</ComboBox>
I just started playing around with Silverlight and a supposedly simple thing like binding a Combobox is driving me nuts. I read a bunch of articles now but none really address the issue that I'm after or were made for Silverlight 2 and don't seem to work.
Let's say I have an entity object "User" which has a "UserStatus" field. In the database UserStatus field is defined as byte and in code it's defined as:
public enum UserStatus : byte
{
Active = 1,
Locked = 2,
Suspended = 3,
}
When ADO.NET entity framework creates the user entity it leaves the UserStatus field as byte. So, to address this I stumbled across IValueConverter and implemented the following:
public class EnumConverter : IValueConverter
{
#region IValueConverter Members
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
switch (parameter.ToString())
{
case "UserStatus":
return ((UserStatus)value).ToString();;
}
return "?";
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
#endregion
}
Now, I also need to supply the Combobox an ItemSource, so I implemented this:
internal static class EnumValueCache
{
private static readonly IDictionary<Type, object[]> Cache = new Dictionary<Type, object[]>();
public static object[] GetValues(Type type)
{
if (!type.IsEnum)
throw new ArgumentException("Type '" + type.Name + "' is not an enum");
object[] values;
if (!Cache.TryGetValue(type, out values))
{
values = type.GetFields()
.Where(f => f.IsLiteral)
.Select(f => f.GetValue(null))
.ToArray();
Cache[type] = values;
}
return values;
}
}
public class EnumValuesConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value == null)
return null;
switch (parameter.ToString())
{
case "UserStatus":
return EnumValueCache.GetValues(typeof(UserStatus));
}
return null;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
And then finally, this is how I added it to my XAML:
<ComboBox ItemsSource="{Binding UserStatus, Mode=TwoWay, Converter={StaticResource EnumValuesConverter}, ConverterParameter='UserStatus'}"
SelectedItem="{Binding UserStatus, Mode=TwoWay, Converter={StaticResource EnumConverter}, ConverterParameter='UserStatus'}" />
What happens now though is that the ItemsSource gets correctly bound and I see all the options in the dropdown, however, the SelectedItem is not set.
Even when I try to manually set SelectedItem to ="1" or "Active", none of them work.
Can anyone help me out and tell me what's wrong, why I can't seem to get the SelectedItem set?
Thanks,
Tom
I can see two problems with your code.
First, in silverlight 3 the ComboBox matches the object in the SelectedItem to the set of objects in the ItemsSource via the object.Equals method. However your GetValues method returns an array of Boxed enum values. Whereas your EnumConverter returns a string. Hence you asking Silverlight to compare a byte with a string, these are never equal.
Secondly, you need to place some code in the ConvertBack method if you are going to two way bind the SelectedItem (BTW there is no need for a twoway binding the ItemsSource).
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)