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What are Fallback and Target Null Values in WPF?


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Values_WPF

In WPF, Fallback is one of the features of binding fallback values. When we are working with the WPF there are many cases when we get the null values or not the correct binding for handle this type of situation WPF can provide us with Fallback values and Target Null Value. Two types of Fallback values are available.

  1. TargetNullValue
  2. FallbackValue

TargetNullValue is used when we want to display the alternate value when the object property is null. If the object value is null then the TargetNullValue will be set for the target. The target value is set when the bound property is null. Target Null Value defines in the System.Windows.Data namespace.

Syntax
publicobjectTargetNullValue{ get; set; }



Fallback value

Fallback values are used to get or set the value when binding, unable to return a value and when binding fails. If there is a problem with binding or not able to resolve the binding source successfully at that time Fallback values are very useful.

Syntax
publicobjectFallbackValue{ get; set; }

        
    
    



In this example, we can add a source of every image in our project but if any reason that our binding can fail and we want to display our default image so at that moment Fallback value is used.

Let’s took a simple example.

publicclassListofEmployee
        {
           publicstringNameOfEmployee{ get; set; }
           publicintStatusCode{ get; set; }
           publicbool? IsActive{ get; set; }
           publicDateTimeJoiningDate{ get; set; }
           publicDateTime? ResineDate{ get; set; }
        }

Here is a string, bool, int data type now we can set it to null and add their data in target null value.

varem = newListofEmployee();
em.NameOfEmployee = "Ifour Technolab";
em.IsActive = null;
em.JoiningDate = "01-01-2005";
em.ResineDate = null;
this.DataContext = em;

Here, we can set some property null to display alternate data.



         

This is simple binding using this binding format we can get null values. Now we can bind the properties with the target null value.


We can display checkbox checked property is false and set today’s date at this property.

 
   

Let’s see step by step how to create and use TargetNull value and Fallback value.

Step: 1

First of all, start the Visual Studio and select the WPF project.

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Image: Create a WPF project
 

After selecting the WPF App (.NET Framework), give it the appropriate name and click to create a button.

Step: 2

After creating a project just open MainWindow.Xaml file and add the below code or you can create a design that you want to show.

MainWindow.Xaml

    
        
        
    

    
        
            
            
            
            
            
            
            
        
        
            
            
        
        

In this Xaml, we can add Labels, TextBlocks, RadioButton, CheckBox, TextBox, and Button. First, we can set the TargetNullValue and FallbackValue in Name TextBox when the binding fails and no data name can display that time default set name can display same as we can set Date of birth if no date can display then FallbackValue and TargetNullValue can display System date. Otherwise, we can set the default age 18 and set the checkBox checked in Nationality.

 

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Step: 3

Now, create a folder give it to name ViewModel, in the folder create a class file name like MainViewModel, in this view model we can create a bindable property.

usingPrism.Commands;
usingPrism.Mvvm;
using System;
usingSystem.Collections.Generic;
usingSystem.Linq;
usingSystem.Text;
usingSystem.Threading.Tasks;

namespaceFallBackValues.ViewModel
{
publicclassMainViewModel :BindableBase
    {
privatebool _isButtonClicked;
publicboolIsButtonClicked
        {
get{ return _isButtonClicked; }
set{ SetProperty(ref _isButtonClicked, value); }
        }

privatestring _nameofUser;
publicstringNameofUser
        {
get{ return _nameofUser; }
set{ SetProperty(ref _nameofUser, value); }
        }

privateDateTime _dob;
publicDateTime DOB
        {
get{ return _dob; }
set
            {
SetProperty(ref _dob, value);
            }
        }

privatestring _age;
publicstring Age
        {
get{ return _age; }
set
            {
SetProperty(ref _age, value);
            }
        }

privatebool _isNationalityIndian;
publicboolIsNationalityIndian
        {
get{ return _isNationalityIndian = true; }
set{ SetProperty(ref _isNationalityIndian, value); }
        }

privatebool _isMale = false;
publicboolIsMale
        {
get{ return _isMale; }
set
            {
SetProperty(ref _isMale, value);
            }
        }

privatebool _isFeMale = false;
publicboolIsFemale
        {
get{ return _isFeMale; }
set
            {
SetProperty(ref _isFeMale, value);
            }
        }
publicDelegateCommandRegisterButtonClicked{ get; set; }


#region Constructor    
publicMainViewModel()
        {
RegisterButtonClicked = newDelegateCommand(RegisterUser);
        }

#endregion

#region Methods  
privatevoidRegisterUser(objectobj)
        {
IsButtonClicked = true;
        }
#endregion
    }
}
Output:

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Image: Example of TargetNull Value and Fallback Value

Conclusion

In this blog, we have learned how to use fallback values and target null values and when to use them. This is the use of display alternative data when binding fails.

What are Fallback and Target Null Values in WPF?

Values_WPF

In WPF, Fallback is one of the features of binding fallback values. When we are working with the WPF there are many cases when we get the null values or not the correct binding for handle this type of situation WPF can provide us with Fallback values and Target Null Value. Two types of Fallback values are available.

  1. TargetNullValue
  2. FallbackValue

TargetNullValue is used when we want to display the alternate value when the object property is null. If the object value is null then the TargetNullValue will be set for the target. The target value is set when the bound property is null. Target Null Value defines in the System.Windows.Data namespace.

Syntax
publicobjectTargetNullValue{ get; set; }



Fallback value

Fallback values are used to get or set the value when binding, unable to return a value and when binding fails. If there is a problem with binding or not able to resolve the binding source successfully at that time Fallback values are very useful.

Syntax
publicobjectFallbackValue{ get; set; }

        
    
    



In this example, we can add a source of every image in our project but if any reason that our binding can fail and we want to display our default image so at that moment Fallback value is used.

Let’s took a simple example.

publicclassListofEmployee
        {
           publicstringNameOfEmployee{ get; set; }
           publicintStatusCode{ get; set; }
           publicbool? IsActive{ get; set; }
           publicDateTimeJoiningDate{ get; set; }
           publicDateTime? ResineDate{ get; set; }
        }

Here is a string, bool, int data type now we can set it to null and add their data in target null value.

varem = newListofEmployee();
em.NameOfEmployee = "Ifour Technolab";
em.IsActive = null;
em.JoiningDate = "01-01-2005";
em.ResineDate = null;
this.DataContext = em;

Here, we can set some property null to display alternate data.



         

This is simple binding using this binding format we can get null values. Now we can bind the properties with the target null value.


We can display checkbox checked property is false and set today’s date at this property.

 
   

Let’s see step by step how to create and use TargetNull value and Fallback value.

Step: 1

First of all, start the Visual Studio and select the WPF project.

ai-Hiring-banner

Image: Create a WPF project
 

After selecting the WPF App (.NET Framework), give it the appropriate name and click to create a button.

Step: 2

After creating a project just open MainWindow.Xaml file and add the below code or you can create a design that you want to show.

MainWindow.Xaml

    
        
        
    

    
        
            
            
            
            
            
            
            
        
        
            
            
        
        

In this Xaml, we can add Labels, TextBlocks, RadioButton, CheckBox, TextBox, and Button. First, we can set the TargetNullValue and FallbackValue in Name TextBox when the binding fails and no data name can display that time default set name can display same as we can set Date of birth if no date can display then FallbackValue and TargetNullValue can display System date. Otherwise, we can set the default age 18 and set the checkBox checked in Nationality.

 

Wants to Talk with Our Highly Skilled WPF Developer ?

Contact Now.


Step: 3

Now, create a folder give it to name ViewModel, in the folder create a class file name like MainViewModel, in this view model we can create a bindable property.

usingPrism.Commands;
usingPrism.Mvvm;
using System;
usingSystem.Collections.Generic;
usingSystem.Linq;
usingSystem.Text;
usingSystem.Threading.Tasks;

namespaceFallBackValues.ViewModel
{
publicclassMainViewModel :BindableBase
    {
privatebool _isButtonClicked;
publicboolIsButtonClicked
        {
get{ return _isButtonClicked; }
set{ SetProperty(ref _isButtonClicked, value); }
        }

privatestring _nameofUser;
publicstringNameofUser
        {
get{ return _nameofUser; }
set{ SetProperty(ref _nameofUser, value); }
        }

privateDateTime _dob;
publicDateTime DOB
        {
get{ return _dob; }
set
            {
SetProperty(ref _dob, value);
            }
        }

privatestring _age;
publicstring Age
        {
get{ return _age; }
set
            {
SetProperty(ref _age, value);
            }
        }

privatebool _isNationalityIndian;
publicboolIsNationalityIndian
        {
get{ return _isNationalityIndian = true; }
set{ SetProperty(ref _isNationalityIndian, value); }
        }

privatebool _isMale = false;
publicboolIsMale
        {
get{ return _isMale; }
set
            {
SetProperty(ref _isMale, value);
            }
        }

privatebool _isFeMale = false;
publicboolIsFemale
        {
get{ return _isFeMale; }
set
            {
SetProperty(ref _isFeMale, value);
            }
        }
publicDelegateCommandRegisterButtonClicked{ get; set; }


#region Constructor    
publicMainViewModel()
        {
RegisterButtonClicked = newDelegateCommand(RegisterUser);
        }

#endregion

#region Methods  
privatevoidRegisterUser(objectobj)
        {
IsButtonClicked = true;
        }
#endregion
    }
}
Output:

ai-Hiring-banner

Image: Example of TargetNull Value and Fallback Value

Conclusion

In this blog, we have learned how to use fallback values and target null values and when to use them. This is the use of display alternative data when binding fails.