How to bind inverse boolean properties in WPF

Question

What I have is an object that has an IsReadOnly property  If this property is true  I would like to set the IsEnabled property on a Button    for example    to false   I would like to believe that I can do it as easily as IsEnabled   Binding Path  IsReadOnly   but that doesn t fly with WPF   Am I relegated to having to go through all of the style settings  Just seems too wordy for something as simple as setting one bool to the inverse of another bool    lt Button Style gt       lt Style TargetType   x Type Button   gt           lt Style Triggers gt               lt DataTrigger Binding   Binding Path IsReadOnly   Value  True  gt                   lt Setter Property  IsEnabled  Value  False    gt               lt  DataTrigger gt               lt DataTrigger Binding   Binding Path IsReadOnly   Value  False  gt                   lt Setter Property  IsEnabled  Value  True    gt               lt  DataTrigger gt           lt  Style Triggers gt       lt  Style gt   lt  Button Style gt

User · Answer

I wanted my XAML to remain as elegant as possible so I created a class to wrap the bool which resides in one of my shared libraries, the implicit operators allow the class to be used as a bool in code-behind seamlessly

public class InvertableBool
{
    private bool value = false;

    public bool Value { get { return value; } }
    public bool Invert { get { return !value; } }

    public InvertableBool(bool b)
    {
        value = b;
    }

    public static implicit operator InvertableBool(bool b)
    {
        return new InvertableBool(b);
    }

    public static implicit operator bool(InvertableBool b)
    {
        return b.value;
    }

}

The only changes needed to your project are to make the property you want to invert return this instead of bool

    public InvertableBool IsActive 
    { 
        get 
        { 
            return true; 
        } 
    }

And in the XAML postfix the binding with either Value or Invert

IsEnabled="{Binding IsActive.Value}"

IsEnabled="{Binding IsActive.Invert}"

User · Answer

With standart binding you need to use converters that looks little windy  So  I recommend you to look at my project CalcBinding  which was developed specially to resolve this problem and some others  With advanced binding you can write expressions with many source properties directly in xaml  Say  you can write something like    lt Button IsEnabled   c Binding Path  IsReadOnly     gt    or   lt Button Content   c Binding ElementName grid  Path ActualWidth Height    gt    or   lt Label Content   c Binding A B C      gt    or   lt Button Visibility   c Binding IsChecked  FalseToVisibility Hidden     gt    where A  B  C  IsChecked - properties of viewModel and it will work properly

User · Answer

I did something very similar   I created my property behind the scenes that enabled the selection of a combobox ONLY if it had finished searching for data   When my window first appears  it launches an async loaded command but I do not want the user to click on the combobox while it is still loading data  would be empty  then would be populated    So by default the property is false so I return the inverse in the getter   Then when I m searching I set the property to true and back to false when complete   private bool  isSearching  public bool IsSearching       get   return   isSearching        set               if  isSearching    value                         isSearching   value              OnPropertyChanged  IsSearching                       public CityViewModel         LoadedCommand   new DelegateCommandAsync LoadCity  LoadCanExecute      private async Task LoadCity object pArg        IsSearching   true           Do your searching task here        IsSearching   false     private bool LoadCanExecute object pArg        return IsSearching      Then for the combobox I can bind it directly to the IsSearching    lt ComboBox ItemsSource   Binding Cities   IsEnabled   Binding IsSearching   DisplayMemberPath  City    gt

User · Answer

Don t know if this is relevant to XAML  but in my simple Windows app I created the binding manually and added a Format event handler   public FormMain       InitializeComponent       Binding argBinding   new Binding  Enabled   uxCheckBoxArgsNull   Checked   false  DataSourceUpdateMode OnPropertyChanged     argBinding Format    new ConvertEventHandler Binding Format BooleanInverse     uxTextBoxArgs DataBindings Add argBinding      void Binding Format BooleanInverse object sender  ConvertEventArgs e      bool boolValue    bool e Value    e Value    boolValue

User · Answer

I had an inversion problem  but a neat solution   Motivation was that the XAML designer would show an empty control e g  when there was no datacontext   no MyValues  itemssource    Initial code  hide control when MyValues is empty   Improved code  show control when MyValues is NOT null or empty   Ofcourse the problem is how to express  1 or more items   which is the opposite of 0 items    lt ListBox ItemsSource  Binding MyValues   gt     lt ListBox Style x Uid  F404D7B2-B7D3-11E7-A5A7-97680265A416  gt       lt Style TargetType   x Type ListBox   gt         lt Style Triggers gt           lt DataTrigger Binding   Binding MyValues Count   gt             lt Setter Property  Visibility  Value  Collapsed   gt           lt  DataTrigger gt         lt  Style Triggers gt       lt  Style gt     lt  ListBox Style gt   lt  ListBox gt    I solved it by adding    lt DataTrigger Binding   Binding MyValues Count  FallbackValue 0  TargetNullValue 0   gt    Ergo setting the default for the binding  Ofcourse this doesn t work for all kinds of inverse problems  but helped me out with clean code

User · Answer

I use a similar approach like  Ofaim  private bool jobSaved   true  private bool JobSaved            get   gt  jobSaved       set               if  value    jobSaved  return          jobSaved   value           OnPropertyChanged            OnPropertyChanged  EnableSaveButton             public bool EnableSaveButton   gt   jobSaved

User · Answer

Have you considered an IsNotReadOnly property  If the object being bound is a ViewModel in a MVVM domain  then the additional property makes perfect sense  If it s a direct Entity model  you might consider composition and presenting a specialized ViewModel of your entity to the form

User · Answer

I would recommend using https   quickconverter codeplex com   Inverting a boolean is then as simple as   lt Button IsEnabled   qc Binding    P   P  Binding IsReadOnly      gt   That speeds the time normally needed to write converters

User · Answer

Net Core Solution   Handles null situation and does not throw an exception  but returns true if no value is presented  otherwise takes the inputted Boolean and reverses it   public class BooleanToReverseConverter   IValueConverter       public object Convert object value  Type targetType  object parameter  CultureInfo culture         gt    bool   value    true       public object ConvertBack object value  Type targetType  object parameter  CultureInfo culture         gt    value as bool        Xaml  IsEnabled   Binding IsSuccess Converter  StaticResource BooleanToReverseConverter        App Xaml I like to put all my converter statics in the app xaml file so I don t have to redeclare them throughout the windows pages controls of the project     lt Application Resources gt       lt converters BooleanToReverseConverter x Key  BooleanToReverseConverter   gt       lt local FauxVM x Key  VM    gt   lt  Application Resources gt      To be clear  converters  is the namespace to the actual class implementation  xmlns converters  clr-namespace ProvingGround Converters

User · Answer

This one also works for nullable bools          ValueConversion typeof bool    typeof bool    public class InverseBooleanConverter   IValueConverter        region IValueConverter Members      public object Convert object value  Type targetType  object parameter  CultureInfo culture                if  targetType    typeof bool                          throw new InvalidOperationException  The target must be a nullable boolean                      bool  b    bool  value          return b HasValue  amp  amp   b Value             public object ConvertBack object value  Type targetType  object parameter  System Globalization CultureInfo culture                return   value as bool                endregion

User · Answer

Following  Paul s answer  I wrote the following in the ViewModel     public bool ShowAtView   get  set    public bool InvShowAtView   get   return  ShowAtView        I hope having a snippet here will help someone  probably newbie as I am  And if there s a mistake  please let me know   BTW  I also agree with  heltonbiker comment - it s definitely the correct approach only if you don t have to use it more than 3 times

User · Answer

Add one more property in your view model  which will return reverse value  And bind that to button  Like   in view model   public bool IsNotReadOnly get return  IsReadOnly      in xaml   IsEnabled   Binding IsNotReadOnly

User · Answer

You can use a ValueConverter that inverts a bool property for you   XAML   IsEnabled   Binding Path IsReadOnly  Converter  StaticResource InverseBooleanConverter      Converter    ValueConversion typeof bool   typeof bool        public class InverseBooleanConverter  IValueConverter                region IValueConverter Members          public object Convert object value  Type targetType  object parameter              System Globalization CultureInfo culture                        if  targetType    typeof bool                   throw new InvalidOperationException  The target must be a boolean                 return   bool value                     public object ConvertBack object value  Type targetType  object parameter              System Globalization CultureInfo culture                        throw new NotSupportedException                        endregion

[wpf] How to bind inverse boolean properties in WPF?

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