I have a user control containing a text box and a label, the label display the length of the input text (with some formatting). I want to change the background color of the text box if the text is longer than 160 characters.
I was thinking of achieving this with bindings, but since the length of the text contain tag to be replaced I'm not willing to have 2 different binding making the same computing.
I don't succeed in changing
I can think of three way to achieves this :
1) create a hidden label with all tags replaced in his text, then have two simple converter to bind display the message length and change the background color. 3 converter for such a basic task seems too much to me.
2) Use the text_changed event to do the work. This work but it seems to me its not the way to do things in WPF.
3) Use a multibinding and pass my form as a source, this should work but looks too much 'god object' approach to me.
What do you think of that ? Am I missing a cleaner/simpler solution ?
Any suggestion is welcome, Thanks in advance.
You can create another property TBBackColor, and bind your textbox BackgroundColor to it.
Something like:
Public System.Windows.Media.Brush TBBackColor
{
get
{
return (TBText.Length>160)? new SolidColorBrush(Color.Red): new SolidColorBrush(Color.White);
}
}
And remember in your TBText property (if that is the one bind to your TextBox: Text) you need to raise propertychanged event for TBBackColor too.
Using a converter is a good idea in this case, but you won't need multiple converters. Instead, we define one converter with multiple parameters:
public class TextBoxValueConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value == null || string.IsNullOrEmpty(parameter as string))
throw new ArgumentException("Invalid arguments specified for the converter.");
switch (parameter.ToString())
{
case "labelText":
return string.Format("There are {0} characters in the TextBox.", ((string)value).Count());
case "backgroundColor":
return ((string)value).Count() > 20 ? Brushes.SkyBlue : Brushes.White;
default:
throw new ArgumentException("Invalid paramater specified for the converter.");
}
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
And then in your XAML you use it like this:
<TextBox Name="textBox" Background="{Binding RelativeSource={RelativeSource Self}, Path=Text, Converter={StaticResource converter}, ConverterParameter=backgroundColor}"/>
<Label Content="{Binding ElementName=textBox, Path=Text, Converter={StaticResource converter}, ConverterParameter=labelText}"/>
Related
I'm sitting in front of the following unit test without getting it to work properly
[TestMethod]
public void EvenIndexesZeroShouldHaveWhiteBackground()
{
var converterBinding = new Binding("BackgroundConverter");
converterBinding.Converter = new BackgroundConverter();
var lvi0 = new ListViewItem() { Background = Brushes.Gray };
var lv = new ListView();
lvi0.SetBinding(ListViewItem.BackgroundProperty, converterBinding);
lv.Items.Add(lvi0);
Assert.AreEqual(Brushes.White, converterBinding.Converter.Convert(lvi0, null, null, CultureInfo.InvariantCulture));
}
I was able to get another converter tested by directly calling the Convert(...) method, but it received a simple data type.
I have the feeling that I somehow need to trigger the converter when adding lvi0to the ListView(or manually afterwards) but I don't know how to do it.
Can anyone point me in the right direction?
I'm new to WPF and haven't fully gotten my head around the Bindings and Dependency Properties yet :(
[UPDATE]
The current problem is that the Convertmethod isn't called. It's not the content of the converter or the result it is giving back.
[UPDATE 2]
#Tatranskymedved comment pointed me into the right direction and calling the converter directly (as proposed by #PeterDuniho) now works. I have updated the code snippet above accordingly.
[UPDATE 3]
Here is the Converter. I HAVE to pass in a ListViewItem since this is what the it is working on. Changing it is currently not an option.
public class BackgroundConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
ListViewItem item = value as ListViewItem;
if (item == null) return Brushes.White;
ListView listView = ItemsControl.ItemsControlFromItemContainer(item) as ListView;
// Get the index of a ListViewItem
if (listView == null)
return Brushes.White;
int index = listView.ItemContainerGenerator.IndexFromContainer(item);
if (index % 2 == 0)
{
return Brushes.WhiteSmoke;
}
return Brushes.White;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotSupportedException();
}
}
The basic idea is: In WPF You are using some Window/UserControl, where are layouts and controls. If any of the controls should have binded its property to the ViewModel, property of the Control must be defined as DependencyProperty. If You are just using some already defined controls, You do not need to known them.
When You are creating own UserControl, it has to have a DependencyProperty, so You can bind one end to it.
Now You have to realize, what do You want to test. Is it the binding? Or the converter itself?
For the binding test, You can refer to this: Unit test WPF Bindings
Or: http://www.wpf-tutorial.com/data-binding/debugging/
However, talking about unit tests, You should test the Converter directly instead of putting them to the complicated chain objects like Binding. That is the basic motivation if the test won't work, You can say "the problem is with the Converter", not with the binding or the object You will bind to.
Only thing You need to check if the type of value You setting is the correct one. For WPF Control's BackgroundProperty it should be System.Windows.Media.Brush as on MSDN.
I have a TextBox that whenever a user types into it I want the text to only be uppercase. For example, if I type in "abc" the actual text in the TextBox and in the backend binding should be "ABC".
In WPF there is the CharacterCasing property, but I can't seem to find that in Windows XAML (or whatever you call a Windows 8 app).
I tried making a converter, but that didn't seem to work:
Converter:
public class UpperCaseConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, string language)
{
return value.ToString().ToUpper();
}
public object ConvertBack(object value, Type targetType, object parameter, string language)
{
return value.ToString().ToUpper();
}
}
XAML:
<TextBox Text="{Binding ElementName=uiMainPage, Path=Company, Mode=TwoWay, Converter={StaticResource ToUpper}}"/>
This is the code I made for it in VB.Net but it should be easy to translate to C#
Make a textchanged event for your textboxes and call a method giving it your sender as a textbox
Private Sub AnyTextBox_TextChanged(sender As Object, e As TextChangedEventArgs)
TextBoxToChange = (CType(sender,Textbox))
TextBoxToChange.Text = TextBoxToChange.Text.ToUpper()
TextBoxToChange.SelectionStart = TextBoxToChange.Text.Length
End Sub
The TextChanged event takes the textbox and changes the text to uppercase (The selectionstart is to stop the selection of the textbox to go back to 0 which causes to write backwards )
You will have XAML looking like this
<TextBox x:Name="txtTest1"
TextChanged="AnyTextBox_TextChanged"/>
<TextBox x:Name="txtTest2"
TextChanged="AnyTextBox_TextChanged"/>
It is not exactly a converter as you wish but it will do the trick just fine and this will only be 1 method per page
After searching and trying several options over the last week, I can't seem to find what I am looking for; maybe someone here can help. While reading through this, please keep in mind that I am attempting to utilize MVVM as strictly as possible, though I am relatively new to WPF. As a side note, I am using Mahapps.Metro to style my window and controls, found here.
I have an XML file that my application uses for configuration (I cannot use the app.config file because the application cannot install on the users' systems). The application will look for this file at start-up and if it does not find the file, it will create it. Below is a snippet of the XML:
<?xml version="1.0" encoding="utf-8"?>
<prefRoot>
<tabReport>
<cbCritical>True</cbCritical>
</tabReport>
</prefRoot>
I reference the XML file in my Window.Resources:
<Controls:MetroWindow.Resources>
<XmlDataProvider x:Key="XmlConfig"
Source="%appdata%\Vulnerator\Vulnerator_Config.xml"
XPath="prefRoot"
IsAsynchronous="False"
IsInitialLoadEnabled="True"/>
</Controls:MetroWindow.Resources>
And utilize this as the DataContext for my MainWindow:
<Controls:MetroWindow DataContext="{DynamicResource XmlConfig}">
Next, I set up a "string-to-bool" converter:
class StringToBoolConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value != null)
{
bool? isChecked = (bool?)value;
return isChecked;
}
return null;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value != null)
{
string isChecked = value.ToString();
return isChecked;
}
return string.Empty;
}
}
Finally, I bind IsChecked to the appropriate XPath:
<Checkbox x:Name="cbCritical"
Content="Critical"
IsChecked="{Binding XPath=//tabReport/cbCritical,
Converter={StaticResource StringToBool}}" />
After all of this, the applciation loads, but IsChecked is set to false... Any and all ideas would be helpful here; thanks in advance!
I figured out the issue... XAML does not handle % in a file path as expected. To correct, I removed the following from my XAML XmlDataProvider declaration:
Source="%appdata%\Vulnerator\Vulnerator_Config.xml"
XPath="prefRoot"
I then set the Source and XPath properties in my code-behind (.xaml.cs):
public MainWindow()
{
InitializeComponent();
Uri xmlPath = new Uri (Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData) + #"\Vulnerator\Vulnerator_Config.xml");
(this.Resources["XmlConfig"] as XmlDataProvider).Source = xmlPath;
(this.Resources["XmlConfig"] as XmlDataProvider).XPath = "prefRoot";
}
Now, when the application loads, the checkbox is set to the inner value of the XML node specified. Also, I set the Binding Mode=TwoWay to OneTime; two way binding to an XmlDataProvider doesn't occur as expected. To get around this, I am going to bind a command to the Checkbox to update a Dictionary<string, string> (created at startup in my view-model constructer) with the new IsChecked value. I will use the Dictionary to control what the application does based off of user input, and write the new Dictionary user values to the XML file once the application is closed.
I require to set text color when text changes inside textbox and meets certain criterion. I can implement this from code behind with textbox_textchanged event and set brushes.color to desired color.
But I am not being able to implement this with xaml wpf approach. I am new to wpf, I'm not sure how can I set text color depending upon certain criterion when text changes in textbox.
For example: For a given textbox, when text changes, it needs to determine if input text is a number then change foreground color to green else red.
Looking forward for the help. Thank you in advance.
I am not sure whether a binding converter is allowed in your situation. But here is a solution which only needs a binding converter in your code behind.
Here is the code in xaml
<Grid.Resources>
<local:ValueConverter x:Key="ValueConverter"></local:ValueConverter>
</Grid.Resources>
<TextBox Text="{Binding Text,UpdateSourceTrigger=PropertyChanged}">
<TextBox.Style>
<Style>
<Style.Triggers>
<DataTrigger Binding="{Binding Path=Text,Converter={StaticResource ValueConverter}}" Value="True">
<Setter Property="TextBox.Foreground" Value="Red"></Setter>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBox.Style>
</TextBox>
Here is the view model and the value converter
public class ViewModel : INotifyPropertyChanged
{
private string _text;
public string Text
{
get
{
return this._text;
}
set
{
this._text = value;
if (null != PropertyChanged)
{
this.PropertyChanged(this, new PropertyChangedEventArgs("Text"));
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
public class ValueConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (null != value)
{
if (value.ToString() == "1")
return true;
}
return false;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return null;
}
}
So the solution uses the data trigger to fulfill the goal. The only reason for using binding converter here is that you need a place to determine what kind of value should change the foreground of the TextBox. Here the foreground of TextBox will be red when the value of the TextBox is "1".
You should just be able to plug into the TextChanged event in wpf and bind a method to this event in the XAML. Then you could check to see if the new values meets your criteria and change the color accordingly.
I'm not really sure what you mean by the "XAML approach" but in this case when you simply want to attach behavior to an event thats raised on one of your controls I do not think that it is wrong to do it the way you have already tried using TextChanged. That's why events are visible in XAML in the first place.
Check the length of the string in the textbox that is being written on every input.
If it is >10 or whatever you want it to be, then change colour.
You could also make that trigger a button that was greyed out.
Sample:
MyTextBlock.Measure(new Size(Double.PositiveInfinity, Double.PositiveInfinity));
return new Size(MyTextBlock.DesiredSize.Width, MyTextBlock.DesiredSize.Height);
Pure xaml? , you might want to look at interactivity, Interaction, Triggers ?
Using EventTrigger in XAML for MVVM – No Code Behind
IMMO I think is better to hook up to code properties/converters/extensions,etc ... for better code reuse , but of course subjective to opinions... and at the end is always up to you.
How do I use an IValueConverter to convert nulls into booleans?
I'm using wpf to try to display a bunch of boolean values (in checkboxes). When a new record is created, these values are null, and appear as 'indeterminate' in the checkboxes. I want the nulls to appear and save as 'false' values.
I tried to create a NullToBoolean converter that takes null values from the database and displays them as false, and then saves them as false when the user hits save. (Essentially, I'm trying to avoid the user having to click twice in the checkboxes (once to make it true, then again to make it false). This seems to work on import - ie null values are shown as false - but unless I do the two-click dance the value doesn't change in the database when I save.
My Converter:
[ValueConversion(typeof(bool), typeof(bool))]
public class NullBooleanConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value != null)
{
return value;
}
return false;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value != null)
{
return value;
}
return null;
}
}
One of the checkboxes I'm trying to have the Converter work with:
<CheckBox Grid.Column="1" Grid.Row="0" Padding="5" Margin="5" VerticalAlignment="Center" Name="chkVarianceDescriptionProvided" IsThreeState="False">
<CheckBox.IsChecked>
<Binding Path="VarianceDescriptionProvided" Mode="TwoWay">
<Binding.Converter>
<utils:NullBooleanConverter />
</Binding.Converter>
</Binding>
</CheckBox.IsChecked>
</CheckBox>
I don't know if the problem is because my code is wrong, or if it's a case of the Converter thinking that nothing has changed, therefore it doesn't need to ConvertBack. I have tried all the Modes and switched code in Convert with ConvertBack, but nothing seems to work.
Can someone point out what I need to do to fix this?
Hmm, why using a converter, if you can have it out of the box?
<CheckBox IsChecked="{Binding VarianceDescriptionProvided, TargetNullValue=False}" />
For more information, pls have a look here.
The real problem is the fact you are not initializing your data objects in the first place. Don't "fix", do it right to begin with; builders are good (for example). You also should be making ViewModels/DataModels rather than working with your Models (database, etc) directly.
public class MyObjectBuilder
{
Checked _checked;
public MyObjectBuilder()
{
Reset()
}
private void Reset()
{
_checked = new Checked(true); //etc
}
public MyObjectBuilder WithChecked(bool checked)
{
_checked = new Checked(checked);
}
public MyObject Build()
{
var built = new MyObject(){Checked = _checked;}
Reset();
return built;
}
}
then always initialise with the builder
myObjects.Add(new MyObjectBuilder().Build());
or
myObjects.Add(_injectedBuilder.Build()); // Initialises Checked to default
myObjects.Add(_injectedBuilder.WithChecked(true).Build()); //True
While this doesn't fix your asked problem, it will fix your underlying problem in a way you can Unit Test. i.e. you can test to ensure the values added into your object list are always initialized.
Simply correct your data before you perform data binding. That is the only option. The converter will only work make the check box show as 'unchecked' and update your data only when you interact with the control. For example:
foreach (var item in items)
{
if (item.VarianceDescriptionProvided == null)
item.VarianceDescriptionProvided = false;
}