I have a class with a List<string> Tags that I want to display in a TextBox. For this I use a IValueConverter.
ListToStringConverter:
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var list = value as List<string>;
var returnvalue = string.Empty;
if(list != null)
list.ForEach(item => returnvalue += item + ", ");
return returnvalue;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
var strValue = value as string;
if(strValue != null)
return strValue.Split(new char[] { ',' });
return null;
}
Class Test:
public class Test : IDataErrorInfo
{
public Test()
{
Tags = new List<string>();
}
public List<string> Tags { get; set; }
string errors;
const string errorsText = "Error in Test class.";
public string Error
{
get { return errors; }
}
public string this[string propertyName]
{
get
{
errors = null;
switch (propertyName)
{
case "Tags":
if (Tags.Count <= 1)
{
errors = errorsText;
return "...more tags plz..";
}
break;
}
return null;
}
}
}
Now I want to Validate the Tags:
<TextBox Text="{Binding Test.Tags, Converter={StaticResource ListToStringConverter}, Mode=TwoWay, ValidatesOnDataErrors=True}" />
But there is no error displayed. Maybe because of the conversion but how can i still accomplish a validation?
I don't see why it shouldn't work. If you will run this at first time - SL will highlight the TextBox with red border. But if you will try to change the list of tags - you will see nothing, because you in your converter you have a bug in ConvertBack you return type array of strings (string[]), but property expects object with type List, so you just need to update the ConvertBack method to:
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
var strValue = value as string;
if (strValue != null)
return strValue.Split(new char[] { ',' }).ToList();
return null;
}
One more note about Convert method, you can use Join method:
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var list = value as List<string>;
if (list != null)
return String.Join(", ", list);
return null;
}
And one more thing about combining the strings. Don't use operator +, because you can have performance issues with it, use StringBuilder instead.
Related
I have a combo-box im populating with a collection of objects in my ViewModel.
<ComboBox x:Name="ChangelistComboBox"
SelectedIndex="{Binding MyObjectSelectionIndex, Mode=TwoWay}"
ItemsSource="{Binding MyObjectList, Mode=OneWay}"
Margin="5"
Grid.Column="0">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Converter={StaticResource MyObjectToComboBoxConverter}}"/>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
Im using a Converter to convert parameters from the object to a displaystring that shows up in the ComboBox
[ValueConversion(typeof(MyObject), typeof(string))]
class MyObjectToComboBoxConverter : ValueConverterBase
{
public override object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
try {
MyObject theObject = (MyObject)value;
int id = theObject.Id;
return (((id != -1) ? id.ToString() : "default") + " : " + theObject.Description);
} catch(InvalidCastException e) {
return (String)value;
}
}
public override object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
return new MyObject(); //Not used
}
}
abstract class ValueConverterBase : IValueConverter
{
public virtual object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
return DependencyProperty.UnsetValue;
}
public virtual object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
return DependencyProperty.UnsetValue;
}
}
In the Model the list is defined as:
private ObservableCollection<MyObject> _MyObjectList;
public ObservableCollection<MyObject> MyObjectList {
get
{
if (_MyObjectList != null) { return _MyObjectList; } else { return new ObservableCollection<MyObject>(); }
}
set
{
if (_MyObjectList != value) {
_MyObjectList = value;
NotifyPropertyChanged("MyObjectList");
}
}
}
In the ViewModel the MyObjectList is simply referenced from the model through the interface:
public ObservableCollection<MyObject> MyObjectList {
get
{
if (Model != null) {
return Model.MyObjectList;
} else {
return new ObservableCollection<MyObject>();
}
}
}
Without the TryCatch, this converter crashes when my MyObjectList is updated. It gives an error like Cannot cast type string to object on the MyObject theObject = (MyObject)value; line
With the TryCatch the converter works as intended. It even returns a correctly assembled string. The problem is I get InvalidCastExceptions in the error log, which isnt good. Also I have no idea why it works despite the exception.
The only hunch I have is that for some reason the object is being converted twice, once from object to string and then it tries to convert the string to string and fails there. I cant figure out why it would be doing that though.
MVVM IValueConverter Convert method getting empty string argument when expecting a float
Just found this which seems to be the same issue that I'm experiencing. I dont fully understand the explanation for it given there, but if modifying the Convert to accept an empty string is a viable solution i can live with that
Still feels like a hack but beggars cant be choosers i guess
You bind the ComboBox source to a list of MyObject, so the value should never be of type string. I guess there is a problem in your model state.
The way you are binding your view is correct, also the first version of the converter:
[ValueConversion(typeof(MyObject), typeof(string))]
class MyObjectToComboBoxConverter : IValueConverter
{
public override object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
try {
var theObject = (MyObject)value;
var id = theObject.Id;
return (((id != -1) ? id.ToString() : "default") + " : " + theObject.Description);
} catch(InvalidCastException e) {
return (string)value;
}
}
public override object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
throw new NotImplementedException();
}
}
Please start to change your ViewModel to:
public ObservableCollection<MyObject> MyObjectList { get; set; } = new ObservableCollection<MyObject>();
You need to implement the OnPropertyChangeEvent on the properties of the MyObject model (https://learn.microsoft.com/en-us/dotnet/framework/wpf/data/how-to-create-and-bind-to-an-observablecollection)
so you only need to set the ObservableCollection in your ViewModel to an empty instance by default.
Then adding items:
MyObjectList.Add(new MyObject{ id=1, Description="First"});
I'm using a Type Converter to do some string manipulations on text being bound to TextBlocks in a UWP app. I used a type converter class that I have used in a number of UWP apps with no issues. But in a new UWP app I keep seeing the issue where the Binding value gets passed back and no changes have been made in the type converter to my passed values. I had been using a type converter that takes parameters to take custom actions and that isn't working as well as a simple new type converter I created. The odd thing is that the type converters work at run-time but as ignored at design-time.
Here are the parts of my code and XAML:
This is a data class that creates sample data for this repro to use for my bindings:
public class Alerts_DataClass
{
public string id { get; set; }
public string severity { get; set; }
public string status { get; set; }
public string title { get; set; }
public DateTime lastEventTime { get; set; }
}
public class AlertsSampleData : Alerts_DataClass
{
public AlertsSampleData()
{
Alerts_DataClass myAlert = new Alerts_DataClass { id = "636531490526731751_2124891065", title = "Category Type XVI", severity = "Medium", lastEventTime = new DateTime(2018, 2, 02) };
this.id = myAlert.id;
this.status = myAlert.status;
this.title = myAlert.title;
this.lastEventTime = myAlert.lastEventTime;
this.severity = myAlert.severity;
}
}
Here is the XAML:
<Page
x:Class="NestedBindingsTester.TypeConverterTest"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:NestedBindingsTester"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:sys="using:System"
mc:Ignorable="d">
<Page.Resources>
<local:StringFormatConverterWithChangeType x:Key="StringFormatConverter"/>
<local:DebugDataBindingConverter x:Key="DebugBinding"/>
<local:ValueToStringConverter x:Key="valueToStringConverter" />
<local:AlertsSampleData x:Key="data2"/>
</Page.Resources>
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<Grid.RowDefinitions>
<RowDefinition Height="103*"/>
<RowDefinition Height="897*"/>
</Grid.RowDefinitions>
<StackPanel Grid.Row="1" d:DataContext="{StaticResource data2}">
<TextBlock Text="{Binding title, ConverterParameter=lower, Converter={StaticResource StringFormatConverter}, Mode=TwoWay}" Style="{StaticResource BaseTextBlockStyle}" Margin="50,0,0,0" />
<TextBlock Text="{Binding title, Converter={StaticResource valueToStringConverter}, Mode=TwoWay}" Style="{StaticResource BaseTextBlockStyle}" Margin="50,0,0,0" />
</StackPanel>
</Grid>
</Page>
And finally here are the two Type Converter modules. The first is the simple one, valueToStringConverter which I just have take any String text passed and return it as lower case:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Windows.UI.Xaml.Data;
namespace NestedBindingsTester
{
public sealed class ValueToStringConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, string language)
{
//return value?.ToString();
string strThisTest = value.ToString().ToLower();
return strThisTest;
}
public object ConvertBack(object value, Type targetType, object parameter, string language)
{
throw new NotImplementedException("Converting from string is not supported.");
}
}
}
And the original type converter I was using that takes parameters as switches for various actions called StringFormatConverter. In my XAML example I am passing the parameter of 'lower' to tell it to convert the string value to lowercase:
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
using System.Linq;
using System.Runtime.Serialization;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using Windows.UI.Xaml.Data;
namespace NestedBindingsTester
{
public class DebugDataBindingConverter : IValueConverter
{
public object Convert(object value, Type targetType,
object parameter, CultureInfo culture)
{
Debugger.Break();
return "This is";
////return value;
}
public object ConvertBack(object value, Type targetType,
object parameter, CultureInfo culture)
{
Debugger.Break();
return "it";
////return value;
}
public object Convert(object value, Type targetType, object parameter, string language)
{
////throw new NotImplementedException();
return "Hello moto";
}
public object ConvertBack(object value, Type targetType, object parameter, string language)
{
throw new NotImplementedException();
}
}
/// <summary>
/// Sample usage:
/// Text="{Binding Budget, Mode=TwoWay, Converter={StaticResource StringFormatConverterWithChangeType}, ConverterParameter='\{0:C2\}'}"
/// </summary>
public class StringFormatConverterWithChangeType : IValueConverter
{
#region IValueConverter Members
public object Convert(object value, Type targetType, object parameter, string language)
{
// Used in UWP app
//
if (value != null)
{
// Arbitrarily remove dollar sign.
//value = value.ToString().Replace("$", "");
}
else
{
value = "**NULL**";
}
if (parameter != null)
{
string formatString = parameter.ToString();
if (!string.IsNullOrEmpty(formatString))
{
string strValue = value.ToString();
if (strValue != null && !string.IsNullOrWhiteSpace(strValue))
{
switch (formatString)
{
case "%": // Add %
return String.Format("{0}%", value);
case "mi": // Add miles
return String.Format("{0} miles", value);
case "caps": // Convert to Initial caps
return UpperCaseFirstCharacter(value.ToString());
case "lower": // Convert to Initial caps
return value.ToString().ToLower();
case "LiGa": // Convert from Liters to Gallons
{
//
// Convert kilometers to miles.
// 1 liter = 0.264172052 US gallons
//
double lConversion = 0.264172052;
double liters = System.Convert.ToDouble(strValue);
double gallons = lConversion * liters;
return String.Format("{0:N1} gallons", gallons);
}
case "TimeMath": // Compute time remaining until fully charged
{
int Minutes = System.Convert.ToInt16(value);
DateTime currentTime = DateTime.Now;
TimeSpan twoAndAHalfHours = new TimeSpan(0, Minutes, 0);
DateTime estimatedFullChargedTime = DateTime.Now.AddMinutes(Minutes);
string formattedTime = estimatedFullChargedTime.ToString("HH:mm");
return formattedTime;
}
case "UTCtoShortDate": // 02/03.2018
{
string utcDate = value.ToString(); // "2018-01-26T02:17:23.5099802Z";
DateTime dateTime;
DateTime.TryParse(utcDate, CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal, out dateTime);
Debug.WriteLine(dateTime.ToString());
string strWDATP_Date = String.Format("{0:MM.dd.yyyy}", dateTime);
return strWDATP_Date;
}
case "{0:d}": // Short date.
case "{0:D}": // Long date.
////return String.Format(culture, formatString, System.Convert.ChangeType(value, typeof(DateTime), null));
return String.Format("US", formatString, System.Convert.ChangeType(value, typeof(DateTime), null));
}
}
else
{
return String.Format("US", formatString, value);
}
}
}
return value.ToString();
}
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value != null)
{
// Arbitrarily remove dollar sign.
//value = value.ToString().Replace("$", "");
}
if (parameter != null)
{
string formatString = parameter.ToString();
if (!string.IsNullOrEmpty(formatString))
{
string strValue = value.ToString();
if (strValue != null && !string.IsNullOrWhiteSpace(strValue))
{
switch (formatString)
{
case "%": // Add %
return String.Format("{0}%", value);
case "mi": // Add miles
return String.Format("{0} miles", value);
case "caps": // Convert to Initial caps
return UpperCaseFirstCharacter(value.ToString());
case "LiGa": // Convert from Liters to Gallons
{
//
// Convert kilometers to miles.
// 1 liter = 0.264172052 US gallons
//
double lConversion = 0.264172052;
double liters = System.Convert.ToDouble(strValue);
double gallons = lConversion * liters;
return String.Format("{0:N1} gallons", gallons);
}
case "TimeMath": // Compute time remaining until fully charged
{
int Minutes = System.Convert.ToInt16(value);
DateTime currentTime = DateTime.Now;
TimeSpan twoAndAHalfHours = new TimeSpan(0, Minutes, 0);
DateTime estimatedFullChargedTime = DateTime.Now.AddMinutes(Minutes);
string formattedTime = estimatedFullChargedTime.ToString("HH:mm");
return formattedTime;
}
case "{0:d}": // Short date.
case "{0:D}": // Long date.
return String.Format(culture, formatString, System.Convert.ChangeType(value, typeof(DateTime), null));
}
}
else
{
return String.Format(culture, formatString, value);
}
}
}
return value.ToString();
}
public object ConvertBack(object value, Type targetType, object parameter, string language)
{
throw new NotImplementedException();
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return value;
}
public string UpperCaseFirstCharacter(string text)
{
//return Regex.Replace(text, "^[a-z]", m => m.Value.ToUpper());
return text.First().ToString().ToUpper() + text.Remove(0, 1).ToLower();
}
#endregion
};
}
I am using Visual Studio 2017 and targeting the Windows 10 Fall Creators Update SDK (16299).
I just can't spot why it's no longer working as these type converters have been working fine in two other UWP projects.
NOTE: I am using Binding in my binding for the TextBlocks since x:Bind does not work with design-time data.
Thanks for taking a look, I have been staring at this code for a while and can't find the problem.
Rick
Using a TextBox in WPF I have the problem that if I use ',' instead of '.' every time I try to get the value, the text inside the TextBox is transformed with the same number without comma..
How can I disable this automatic transformation?
<TextBox
x:Name="XValue"
Text="{Binding XInitValue, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
Width="80" VerticalAlignment="Center"
TextChanged="XValue_TextChanged"
</TextBox>
private void XValue_TextChanged(object sender, TextChangedEventArgs e)
{
double a = XInitValue;
}
I solved it using an converter
public class DecimalConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if(CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator == ".")
return value.ToString().Replace(",", ".");
else
return value.ToString().Replace(".", ",");
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
if (CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator == ".")
return value.ToString().Replace(".", ",");
else
return value.ToString().Replace(",", ".");
}
}
It really works! Thanks!
I have change it a bit to be more general, not use the CurrentCulture in the converter itself and return error if the entered value is ended with decimal separator. Without last part I could not enter the decimal separator at all if the UpdateSourceTrigger=PropertyChanged.
public class DecimalConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value == null)
{
return null;
}
if (value is string stringValue && targetType == typeof(decimal))
{
var decSeparator = culture.NumberFormat.NumberDecimalSeparator;
var normString = decSeparator == "."
? stringValue.Replace(",", ".")
: stringValue.Replace(".", ",");
if (!normString.EndsWith(decSeparator) && decimal.TryParse(normString, out var decResult))
{
return decResult;
}
}
return DependencyProperty.UnsetValue;
}
}
Certainly the CurrentCulture should be set in App.xml.cs or somewhere else on starting the application:
var culture = CultureInfo.GetCultureInfo("de-DE");
Thread.CurrentThread.CurrentCulture = culture;
Thread.CurrentThread.CurrentUICulture = culture;
FrameworkElement.LanguageProperty.OverrideMetadata(
typeof(FrameworkElement),
new FrameworkPropertyMetadata(
XmlLanguage.GetLanguage(culture.IetfLanguageTag)));
I'm pretty new to XAML and WPF, and I'm trying to build a Converter, which converts an integer to a month (string)
I know the code below doesn't work because it gets an object rather than a string to process, but I have no idea how to handle this object?
public class NumberToMonthConverter : IValueConverter
{
public object Convert(object value, Type targetType,
object parameter, CultureInfo culture)
{
if (value is int)
{
string strMonthName = CultureInfo.CurrentCulture.DateTimeFormat.GetMonthName(value);
return strMonthName;
}
}
}
You are pretty close, just cast value to int after you checked it is an int:
if (value is int)
{
return CultureInfo.CurrentCulture.DateTimeFormat.GetMonthName((int)value);
}
else // you need this since you need to return a value
{ // throw an exception if the value is unexpected
throw new ArgumentException("value is not an int", "value");
}
why dont use TryParse?
int i;
if (int.TryParse(value, out i)) {
string strMonthName = CultureInfo.CurrentCulture.DateTimeFormat.GetMonthName(i);
return strMonthName;
}
else {
throw new Exception("value is not int!");
--OR--
return "Jan"; //For example
}
Lets say i have an activity with InArgument<int> ProductId
I'd like to expose in the activity designer a combobox to show all Products and the user can select a product.
I can show the list of product in the combo no problem. But how do I bind the selected product to the InArgument<int> of my custom activity?
I suppose I need some kind of ValueConverter? Not sure how to code the value converter for this case, if anybody has an idea, suggestion, will be helpful. I have to convert the InArgument<int> to an int? and the convert back from int to InArgument<int>
Thanks,
public class ArgumentToInt32Converter: IValueConverter {
object IValueConverter.Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
object convertedValue = null;
if (value != null) {
ModelItem argumentModelItem = value as ModelItem;
if (argumentModelItem != null && argumentModelItem.Properties["Expression"] != null && argumentModelItem.Properties["Expression"].Value != null) {
if (argumentModelItem.Properties["Expression"].ComputedValue.GetType() == typeof(Literal <Int32> )) {
convertedValue = (argumentModelItem.Properties["Expression"].ComputedValue as Literal <Int32> ).Value;
} else {
convertedValue = null
}
}
}
return convertedValue;
}
object IValueConverter.ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
// Convert Int32 value to InArgument<Int32>
Int32 itemContent = (Int32) value;
VisualBasicValue <Int32> vbArgument = new VisualBasicValue <Int32> (itemContent);
InArgument <Int32> inArgument = new InArgument <Int32> (vbArgument);
return inArgument;
}
}
Modified from this answer
This is my attempt at making a more generic solution to this. I have several properties - some IEnumerable, some string, some int, and to make a value converter for each seems like the wrong approach. I'd be interested to know what cases I haven't caught here because I am relatively new to WF. Hopefully this helps someone.
public class ArgumentConverter : IValueConverter
{
#region IValueConverter Members
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
object convertedValue = null;
if(value != null)
{
var argumentModelItem = value as ModelItem;
if(argumentModelItem != null)
{
ModelProperty argumentModelProperty = argumentModelItem.Properties["Expression"];
if(argumentModelProperty != null && argumentModelProperty.Value != null)
{
var computedValue = argumentModelProperty.ComputedValue;
var activity = (Activity) computedValue;
convertedValue = WorkflowInvoker.Invoke(activity)["Result"];
}
}
}
return convertedValue;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
// here targetType should be InArgument<T>
// assume a single generic argument
Type arg0 = targetType.GetGenericArguments()[0];
ConstructorInfo argConstructor = targetType.GetConstructor(new[] {arg0});
var argument = argConstructor.Invoke(new[] { value });
return argument;
}
#endregion
}