DataTrigger where value is NOT null

Question

I know that I can make a setter that checks to see if a value is NULL and do something  Example    lt TextBlock gt     lt TextBlock Style gt       lt Style gt         lt Style Triggers gt           lt DataTrigger Binding   Binding SomeField   Value   x Null   gt             lt Setter Property  TextBlock Text  Value  It s NULL Baby     gt           lt  DataTrigger gt         lt  Style Triggers gt       lt  Style gt     lt  TextBlock Style gt   lt  TextBlock gt    But how can I check for a  not  value    as in  NOT NULL   or  NOT   3   Is that possible in XAML   Results  Thanks for your answers    I knew I could do a value converter  which means I would have to go in code  and that would not be pure XAML as I hoped for   However  that does answer the question that effectively  no  you can t do it in pure XAML  The answer selected  however  shows probably the best way to create that kind of functionality  Good find

User · Accepted Answer

I ran into a similar limitation with DataTriggers, and it would seem that you can only check for equality. The closest thing I've seen that might help you is a technique for doing other types of comparisons other than equality.

This blog post describes how to do comparisons such as LT, GT, etc in a DataTrigger.

This limitation of the DataTrigger can be worked around to some extent by using a Converter to massage the data into a special value you can then compare against, as suggested in Robert Macnee's answer.

User · Answer

If you are looking for a solution that does not use IValueConverter  you can always go with below mechanism          lt StackPanel gt               lt TextBlock Text  Border   Red when null value    gt               lt Border x Name  border objectForNullValueTrigger  HorizontalAlignment  Stretch  Height  20  gt                    lt Border Style gt                       lt Style TargetType  Border  gt                           lt Setter Property  Background  Value  Black    gt                           lt Style Triggers gt                               lt DataTrigger Binding   Binding ObjectForNullValueTrigger   Value   x Null   gt                                   lt Setter Property  Background  Value  Red    gt                               lt  DataTrigger gt                           lt  Style Triggers gt                       lt  Style gt                   lt  Border Style gt               lt  Border gt               lt TextBlock Text  Border   Green when not null value    gt               lt Border HorizontalAlignment  Stretch  Height  20  gt                   lt Border Style gt                       lt Style TargetType  Border  gt                           lt Setter Property  Background  Value  Green    gt                           lt Style Triggers gt                               lt DataTrigger Binding   Binding Background  ElementName border objectForNullValueTrigger   Value  Red  gt                                   lt Setter Property  Background  Value  Black    gt                               lt  DataTrigger gt                           lt  Style Triggers gt                       lt  Style gt                   lt  Border Style gt               lt  Border gt               lt Button Content  Invert Object state  Click  Button Click 1   gt           lt  StackPanel gt

User · Answer

Stop   No converter  I dont want to  sell  the library of this guy  but I hated the fact of doing converter everytime I wanted to compare stuff in XAML    So with this library   https   github com Alex141 CalcBinding  you can do that  and a lot more     First  In the declaration of the windows userControl      lt Windows          xmlns conv  clr-namespace CalcBinding assembly CalcBinding   gt    then  in the textblock   lt TextBlock gt         lt TextBlock Style gt             lt Style Triggers gt             lt DataTrigger Binding   conv Binding  MyValue  null    Value  false  gt                lt Setter Property  Background  Value   FF80C983  gt  lt  Setter gt             lt  DataTrigger gt           lt  Style Triggers gt         lt  TextBlock Style gt       lt  TextBlock gt    The magic part is the conv Binding  MYValue  null    In fact  you could set any condition you wanted  look at the doc      note that I am not a fan of third party   but this library is Free  and little impact  just add 2  dll to the project

User · Answer

You can use a converter or create new property in your ViewModel like that   public bool CanDoIt       get               return  string IsNullOrEmpty SomeField             and use it    lt DataTrigger Binding   Binding SomeField   Value   Binding CanDoIt   gt

User · Answer

lt StackPanel Style gt     lt Style gt       lt Setter Property  StackPanel Visibility  Value  Visible  gt  lt  Setter gt       lt Style Triggers gt         lt DataTrigger  Binding   Binding ElementName ProfileSelectorComboBox  Path SelectedItem Tag   Value   x Null   gt             lt Setter Property  StackPanel Visibility  Value  Collapsed  gt  lt  Setter gt         lt  DataTrigger gt       lt  Style Triggers gt     lt  Style gt   lt  StackPanel Style gt    I just used the inverse logic here   setting my stackpanel to invisible when my comboitem is not populated  it works pretty well

User · Answer

You can use an IValueConverter for this    lt TextBlock gt       lt TextBlock Resources gt           lt conv IsNullConverter x Key  isNullConverter   gt       lt  TextBlock Resources gt       lt TextBlock Style gt           lt Style gt               lt Style Triggers gt                   lt DataTrigger Binding   Binding SomeField  Converter  StaticResource isNullConverter    Value  False  gt                       lt Setter Property  TextBlock Text  Value  It s NOT NULL Baby    gt                   lt  DataTrigger gt               lt  Style Triggers gt           lt  Style gt       lt  TextBlock Style gt   lt  TextBlock gt    Where IsNullConverter is defined elsewhere  and conv is set to reference its namespace    public class IsNullConverter   IValueConverter       public object Convert object value  Type targetType  object parameter  CultureInfo culture                return  value    null              public object ConvertBack object value  Type targetType  object parameter  CultureInfo culture                throw new InvalidOperationException  IsNullConverter can only be used OneWay               A more general solution would be to implement an IValueConverter that checks for equality with the ConverterParameter  so you can check against anything  and not just null

User · Answer

Converter   public class NullableToVisibilityConverter  IValueConverter       public object Convert object value  Type targetType  object parameter  CultureInfo culture                return value    null   Visibility Collapsed   Visibility Visible            Binding   Visibility   Binding PropertyToBind  Converter  StaticResource nullableToVisibilityConverter

User · Answer

You can use an IValueConverter for this    lt TextBlock gt       lt TextBlock Resources gt           lt conv IsNullConverter x Key  isNullConverter   gt       lt  TextBlock Resources gt       lt TextBlock Style gt           lt Style gt               lt Style Triggers gt                   lt DataTrigger Binding   Binding SomeField  Converter  StaticResource isNullConverter    Value  False  gt                       lt Setter Property  TextBlock Text  Value  It s NOT NULL Baby    gt                   lt  DataTrigger gt               lt  Style Triggers gt           lt  Style gt       lt  TextBlock Style gt   lt  TextBlock gt    Where IsNullConverter is defined elsewhere  and conv is set to reference its namespace    public class IsNullConverter   IValueConverter       public object Convert object value  Type targetType  object parameter  CultureInfo culture                return  value    null              public object ConvertBack object value  Type targetType  object parameter  CultureInfo culture                throw new InvalidOperationException  IsNullConverter can only be used OneWay               A more general solution would be to implement an IValueConverter that checks for equality with the ConverterParameter  so you can check against anything  and not just null

User · Answer

I m using this to only enable a button if a listview item  is selected  ie not null     lt Style TargetType   x Type Button   gt       lt Setter Property  IsEnabled  Value  True   gt       lt Style Triggers gt           lt DataTrigger Binding   Binding ElementName lvMyList  Path SelectedItem   Value   x Null   gt               lt Setter Property  IsEnabled  Value  False   gt           lt  DataTrigger gt       lt  Style Triggers gt   lt  Style gt

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You can use DataTrigger class in Microsoft Expression Interactions dll that come with Expression Blend   Code Sample    lt i Interaction Triggers gt       lt i DataTrigger Binding   Binding YourProperty   Value   x Null   Comparison  NotEqual  gt          lt ie ChangePropertyAction PropertyName  YourTargetPropertyName  Value   Binding YourValue    gt       lt  i DataTrigger  lt  i Interaction Triggers gt    Using this method you can trigger against GreaterThan and LessThan too   In order to use this code you should reference two dll s      System Windows Interactivity dll      Microsoft Expression Interactions dll

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This is a bit of a cheat but I just set a default style and then overrode it using a DataTrigger if the value is null        lt Style gt          lt  -- Highlight for Reviewed  Default  -- gt         lt Setter Property  Control Background  Value  PaleGreen    gt          lt Style Triggers gt           lt  -- Highlight for Not Reviewed -- gt           lt DataTrigger Binding   Binding Path REVIEWEDBY   Value   x Null   gt             lt Setter Property  Control Background  Value  LightIndianRed    gt           lt  DataTrigger gt         lt  Style Triggers gt     lt  Style gt

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Compare with null  As Michael Noonan said     lt Style gt       lt Style Triggers gt          lt DataTrigger Binding   Binding SomeProperty   Value   x Null   gt              lt Setter Property  Visibility  Value  Collapsed    gt           lt  DataTrigger gt        lt  Style Triggers gt   lt  Style gt    Compare with not null  without a converter     lt Style gt       lt Setter Property  Visibility  Value  Collapsed    gt       lt Style Triggers gt          lt DataTrigger Binding   Binding SomeProperty   Value   x Null   gt              lt Setter Property  Visibility  Value  Visible    gt           lt  DataTrigger gt        lt  Style Triggers gt   lt  Style gt

User · Answer

lt StackPanel Style gt     lt Style gt       lt Setter Property  StackPanel Visibility  Value  Visible  gt  lt  Setter gt       lt Style Triggers gt         lt DataTrigger  Binding   Binding ElementName ProfileSelectorComboBox  Path SelectedItem Tag   Value   x Null   gt             lt Setter Property  StackPanel Visibility  Value  Collapsed  gt  lt  Setter gt         lt  DataTrigger gt       lt  Style Triggers gt     lt  Style gt   lt  StackPanel Style gt    I just used the inverse logic here   setting my stackpanel to invisible when my comboitem is not populated  it works pretty well

User · Answer

My solution is in the DataContext instance  or ViewModel if using MVVM   I add a property that returns true if the Not Null condition I want is met       Public ReadOnly Property IsSomeFieldNull   As Boolean         Get             Return If SomeField is Null  True  False          End Get     End Property   and bind the DataTrigger to the above property  Note  In VB NET be sure to use the operator If and NOT the IIf function  which doesn t work with Null objects   Then the XAML is        lt DataTrigger Binding   Binding IsSomeFieldNull   Value  False  gt         lt Setter Property  TextBlock Text  Value  It s NOT NULL Baby     gt       lt  DataTrigger gt

User · Answer

You can use DataTrigger class in Microsoft Expression Interactions dll that come with Expression Blend   Code Sample    lt i Interaction Triggers gt       lt i DataTrigger Binding   Binding YourProperty   Value   x Null   Comparison  NotEqual  gt          lt ie ChangePropertyAction PropertyName  YourTargetPropertyName  Value   Binding YourValue    gt       lt  i DataTrigger  lt  i Interaction Triggers gt    Using this method you can trigger against GreaterThan and LessThan too   In order to use this code you should reference two dll s      System Windows Interactivity dll      Microsoft Expression Interactions dll

User · Answer

My solution is in the DataContext instance  or ViewModel if using MVVM   I add a property that returns true if the Not Null condition I want is met       Public ReadOnly Property IsSomeFieldNull   As Boolean         Get             Return If SomeField is Null  True  False          End Get     End Property   and bind the DataTrigger to the above property  Note  In VB NET be sure to use the operator If and NOT the IIf function  which doesn t work with Null objects   Then the XAML is        lt DataTrigger Binding   Binding IsSomeFieldNull   Value  False  gt         lt Setter Property  TextBlock Text  Value  It s NOT NULL Baby     gt       lt  DataTrigger gt

User · Answer

You can use an IValueConverter for this    lt TextBlock gt       lt TextBlock Resources gt           lt conv IsNullConverter x Key  isNullConverter   gt       lt  TextBlock Resources gt       lt TextBlock Style gt           lt Style gt               lt Style Triggers gt                   lt DataTrigger Binding   Binding SomeField  Converter  StaticResource isNullConverter    Value  False  gt                       lt Setter Property  TextBlock Text  Value  It s NOT NULL Baby    gt                   lt  DataTrigger gt               lt  Style Triggers gt           lt  Style gt       lt  TextBlock Style gt   lt  TextBlock gt    Where IsNullConverter is defined elsewhere  and conv is set to reference its namespace    public class IsNullConverter   IValueConverter       public object Convert object value  Type targetType  object parameter  CultureInfo culture                return  value    null              public object ConvertBack object value  Type targetType  object parameter  CultureInfo culture                throw new InvalidOperationException  IsNullConverter can only be used OneWay               A more general solution would be to implement an IValueConverter that checks for equality with the ConverterParameter  so you can check against anything  and not just null

User · Answer

You can use an IValueConverter for this    lt TextBlock gt       lt TextBlock Resources gt           lt conv IsNullConverter x Key  isNullConverter   gt       lt  TextBlock Resources gt       lt TextBlock Style gt           lt Style gt               lt Style Triggers gt                   lt DataTrigger Binding   Binding SomeField  Converter  StaticResource isNullConverter    Value  False  gt                       lt Setter Property  TextBlock Text  Value  It s NOT NULL Baby    gt                   lt  DataTrigger gt               lt  Style Triggers gt           lt  Style gt       lt  TextBlock Style gt   lt  TextBlock gt    Where IsNullConverter is defined elsewhere  and conv is set to reference its namespace    public class IsNullConverter   IValueConverter       public object Convert object value  Type targetType  object parameter  CultureInfo culture                return  value    null              public object ConvertBack object value  Type targetType  object parameter  CultureInfo culture                throw new InvalidOperationException  IsNullConverter can only be used OneWay               A more general solution would be to implement an IValueConverter that checks for equality with the ConverterParameter  so you can check against anything  and not just null

User · Answer

I m using this to only enable a button if a listview item  is selected  ie not null     lt Style TargetType   x Type Button   gt       lt Setter Property  IsEnabled  Value  True   gt       lt Style Triggers gt           lt DataTrigger Binding   Binding ElementName lvMyList  Path SelectedItem   Value   x Null   gt               lt Setter Property  IsEnabled  Value  False   gt           lt  DataTrigger gt       lt  Style Triggers gt   lt  Style gt

User · Answer

Compare with null  As Michael Noonan said     lt Style gt       lt Style Triggers gt          lt DataTrigger Binding   Binding SomeProperty   Value   x Null   gt              lt Setter Property  Visibility  Value  Collapsed    gt           lt  DataTrigger gt        lt  Style Triggers gt   lt  Style gt    Compare with not null  without a converter     lt Style gt       lt Setter Property  Visibility  Value  Collapsed    gt       lt Style Triggers gt          lt DataTrigger Binding   Binding SomeProperty   Value   x Null   gt              lt Setter Property  Visibility  Value  Visible    gt           lt  DataTrigger gt        lt  Style Triggers gt   lt  Style gt

User · Answer

If you are looking for a solution that does not use IValueConverter  you can always go with below mechanism          lt StackPanel gt               lt TextBlock Text  Border   Red when null value    gt               lt Border x Name  border objectForNullValueTrigger  HorizontalAlignment  Stretch  Height  20  gt                    lt Border Style gt                       lt Style TargetType  Border  gt                           lt Setter Property  Background  Value  Black    gt                           lt Style Triggers gt                               lt DataTrigger Binding   Binding ObjectForNullValueTrigger   Value   x Null   gt                                   lt Setter Property  Background  Value  Red    gt                               lt  DataTrigger gt                           lt  Style Triggers gt                       lt  Style gt                   lt  Border Style gt               lt  Border gt               lt TextBlock Text  Border   Green when not null value    gt               lt Border HorizontalAlignment  Stretch  Height  20  gt                   lt Border Style gt                       lt Style TargetType  Border  gt                           lt Setter Property  Background  Value  Green    gt                           lt Style Triggers gt                               lt DataTrigger Binding   Binding Background  ElementName border objectForNullValueTrigger   Value  Red  gt                                   lt Setter Property  Background  Value  Black    gt                               lt  DataTrigger gt                           lt  Style Triggers gt                       lt  Style gt                   lt  Border Style gt               lt  Border gt               lt Button Content  Invert Object state  Click  Button Click 1   gt           lt  StackPanel gt

User · Answer

This is a bit of a cheat but I just set a default style and then overrode it using a DataTrigger if the value is null        lt Style gt          lt  -- Highlight for Reviewed  Default  -- gt         lt Setter Property  Control Background  Value  PaleGreen    gt          lt Style Triggers gt           lt  -- Highlight for Not Reviewed -- gt           lt DataTrigger Binding   Binding Path REVIEWEDBY   Value   x Null   gt             lt Setter Property  Control Background  Value  LightIndianRed    gt           lt  DataTrigger gt         lt  Style Triggers gt     lt  Style gt

User · Answer

Stop   No converter  I dont want to  sell  the library of this guy  but I hated the fact of doing converter everytime I wanted to compare stuff in XAML    So with this library   https   github com Alex141 CalcBinding  you can do that  and a lot more     First  In the declaration of the windows userControl      lt Windows          xmlns conv  clr-namespace CalcBinding assembly CalcBinding   gt    then  in the textblock   lt TextBlock gt         lt TextBlock Style gt             lt Style Triggers gt             lt DataTrigger Binding   conv Binding  MyValue  null    Value  false  gt                lt Setter Property  Background  Value   FF80C983  gt  lt  Setter gt             lt  DataTrigger gt           lt  Style Triggers gt         lt  TextBlock Style gt       lt  TextBlock gt    The magic part is the conv Binding  MYValue  null    In fact  you could set any condition you wanted  look at the doc      note that I am not a fan of third party   but this library is Free  and little impact  just add 2  dll to the project

User · Answer

You can use a converter or create new property in your ViewModel like that   public bool CanDoIt       get               return  string IsNullOrEmpty SomeField             and use it    lt DataTrigger Binding   Binding SomeField   Value   Binding CanDoIt   gt

User · Answer

Converter   public class NullableToVisibilityConverter  IValueConverter       public object Convert object value  Type targetType  object parameter  CultureInfo culture                return value    null   Visibility Collapsed   Visibility Visible            Binding   Visibility   Binding PropertyToBind  Converter  StaticResource nullableToVisibilityConverter

[wpf] DataTrigger where value is NOT null?

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