WPF Input Validation Using MVVM

Data validation is a key part in WPF.

Validation is used to alert the user that the data he entered is illegal.

In this post we will see how to validate user input using MVVM binding.

I have created 2 different templates for input validation:

Click WPFInputValidation Link To Download full source.

Example 1 :

To impelment validation we need to use IDataErrorInfo interface.

IDataErrorInfo  interface provides the functionality to offer custom error information that a user  interface can bind to.

It has 2 Properties :

- Error : Gets an error message indicating what is wrong with this object.

- string this[string columnName] Indexer : it will return the error message for the property. The default is an empty string ("")

 

Let's go through step by step to understand validation with mvvm binding and styling the validation template.

Step 1 :  First change ErrorToolTip style by customizing the Template.

<ControlTemplate x:Key="ErrorToolTipTemplate_1">

 <ControlTemplate.Resources>

  <Style x:Key="textblockErrorTooltip" TargetType="TextBlock">

   <Setter Property="HorizontalAlignment" Value="Center" />

   <Setter Property="VerticalAlignment" Value="Center" />

   <Setter Property="FontWeight" Value="Bold" />

   <Setter Property="Foreground" Value="White" />

   <Setter Property="Margin" Value="10 0 10 0" />

  </Style>

 </ControlTemplate.Resources>

 <DockPanel LastChildFill="true">

  <Border Height="Auto"

   Margin="5,0,0,0"

   Background="#DC000C"

   CornerRadius="3"

   DockPanel.Dock="right">

    <TextBlock Style="{StaticResource textblockErrorTooltip}" 

Text="{Binding ElementName=customAdorner, Path=AdornedElement.(Validation.Errors)[0].ErrorContent}" />

  </Border>

  <AdornedElementPlaceholder Name="customAdorner">

   <Border BorderBrush="#DC000C" BorderThickness="1.3" />

  </AdornedElementPlaceholder>

 </DockPanel>

</ControlTemplate> 

As shown in above source, created ControlTemplate and changed the error tooltip style by Adding Border control in DockPanel, within Border TextBlock placed with Text property binded to the error message set to the property from viewmodel.
 changed Backgroud of the border to Red so it will display error message surround with  border fill with red color. This will dispaly error on right side of the TextBox control. like :

ErrorTemplate uses adorner layer. which is drawing layer, using adorner layer you can add visual appearance to indicate an error without replacing controltemplate.

AdornedElementPlaceholder is part of the Validation feature of data binding. it specify where a decorated control is placed relative to other elements  in the ControlTemplate.

Step 2 : Create TextBox style and set Validation ErrorTemplate.

<Style TargetType="TextBox">

 <Setter Property="HorizontalAlignment" Value="Left" />

 <Setter Property="VerticalAlignment" Value="Top" />

 <Setter Property="Width" Value="150" />

 <Setter Property="Height" Value="30" />

 <Setter Property="Validation.ErrorTemplate" 

                 Value="{DynamicResource ErrorToolTipTemplate_1}" />

 <Style.Triggers>

  <Trigger Property="Validation.HasError" Value="true">

   <Setter Property="ToolTip" 

Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}" />

  </Trigger>

 </Style.Triggers>

</Style> 

Created style of TargetType=TextBox, and Validation.ErrorTemplate is set to previously created template (DynamicResource ErrorToolTipTemplate)

you have to set Resource using DynamicResource, if your temaplate/style is available at global place (App.xaml)
if your control style and template is created in page itself then set resource using StaticResource keyword.

Step 3 : Create ViewModel class, that contains Properties to Bind into view.

public class InputValidationViewModel : ViewModelBase

{

 public InputValidationViewModel()

 {   

 }

 private string employeeName;

 public string EmployeeName

 {

  get { return employeeName; }

  set { employeeName = value; RaisePropertyChanged("EmployeeName"); }

 }

 private string email;

 public string Email

 {

  get { return email; }

  set {email = value; RaisePropertyChanged("Email"); }

 }

 private long phoneNumber;

 public long PhoneNumber

 {

  get { return phoneNumber; }

  set { phoneNumber = value; RaisePropertyChanged("PhoneNumber"); }

 }

 private bool IsValidEmailAddress

 {

  get { return emailRegex.IsMatch(Email); }

 }

} 

as shown in above code, ViewModel created and added some propeties that need to bind in UserControl.

Step 4 : Implement IDataErrorInfo Interface

public class InputValidationViewModel : ViewModelBase, IDataErrorInfo

{

 private Regex emailRegex = new Regex(@"^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$");  

 public InputValidationViewModel()

 {   

 }

        private string error = string.Empty;

 public string Error

 {

  get { return error; }

 }

 public string this[string columnName]

 {

    get

    {

  error = string.Empty;

  if (columnName == "EmployeeName" && string.IsNullOrWhiteSpace(EmployeeName))

  {

   error = "Employee name is required!";

  }

  else if (columnName == "PhoneNumber" && PhoneNumber == 0)

  {

   error = "Phone number is required!";

  }

  else if (columnName == "PhoneNumber" && PhoneNumber.ToString().Length > 10)

  {

   error = "Phone number must have less than or equal to 10 digits!";

  }

  else if (columnName == "Email" && string.IsNullOrWhiteSpace(Email))

  {

   error = "Email address is required!";

  }

  else if (columnName == "Email" && !IsValidEmailAddress)

  {

   error = "Please enter valid email address!";

  }

  return error;

      }

       }

} 

IDataErrorInfo has Error property which returns the validation error that does not match the codition.

in above code, i set the error for each propeties by checking the codition, it coditiion is false then set the error for that property.

For valid email validation, created Regex expression to check entered email address is valid ro not.

This error appear on right side of the control that has property binded.

Step 5 : Last, Add TextBox cotrol in View

<TextBox Grid.Row="1"

 Grid.Column="1"

 Text="{Binding EmployeeName,

           Mode=TwoWay,

           UpdateSourceTrigger=PropertyChanged,

    ValidatesOnDataErrors=True}" /> 

Here EmployeeName proeprty is binded to TextBox control, you have to set ValidatesOnDataErrors=True to throw data error ( entered data is valida or not.)

Mode=TwoWay will allow user to change property from UI as well update UI from ViewModel property.

UpdateSourceTrigger=PropertyChanged will notify changes  is updated as soon as the property changes.

If UpdateSourceTrigger is not set, then TextBox was not immediately sent back to the source. Instead, the source was updated only after focus was lost on the TextBox.

This behavior is controlled by a property on the binding called UpdateSourceTrigger.

Example 2 :


In this example, only ControlTemplate is chaned, other things like : ViewModels Property, Controls are same.

 

As shown in above image, tooltip style is changed, ! mark with red circle surrounded image is added on the errortemplate.

small triangle added on template, to show top right corner of the control if any data error exists.

below are the  template change compare to previous example template :

<Border x:Name="ValidationErrorElement"

 BorderBrush="#FFDB000C"

 BorderThickness="1.2"

 CornerRadius="1"

 ToolTip="{Binding ElementName=customAdorner,

 Path=AdornedElement.(Validation.Errors)[0].ErrorContent}">

 <Grid Width="12"

  Height="12"

  Margin="1,-4,-4,0"

  HorizontalAlignment="Right"

  VerticalAlignment="Top"

  Background="Transparent">

  <Path Margin="1,3,0,0"

        Data="M 1,0 L6,0 A 2,2 90 0 1 8,2 L8,7 z"

        Fill="#FFDC000C" />

  <Path Margin="1,3,0,0"

        Data="M 0,0 L2,0 L 8,6 L8,8"

        Fill="#ffffff" />

 </Grid>

</Border>

<Border Grid.Column="0"

 Width="15"

 Height="15"

 Margin="0 0 3 0"

 HorizontalAlignment="Right"

 VerticalAlignment="Center"

 Background="Red"

 CornerRadius="10"

 ToolTip="{Binding ElementName=customAdorner,

 Path=AdornedElement.(Validation.Errors)[0].ErrorContent}">

 <TextBlock HorizontalAlignment="center"

  VerticalAlignment="center"

  FontWeight="Bold"

  Foreground="white"

  Text="!" />

</Border> 

as shown in above code,

In First border, 2 shapes is created using path, this will create Triangle shape to disply on top right corner of the control.

it will help you to create your custom shapes based on your requirement.

Second border will create red cirlce (by setting CornerRadius proeprty) with ! text wihin cirlce area.

it will display right side of the cotrol, if any data error is there for property.

Conclusion

This way you can create you custom error template for input controls.

Dwonload link

How to turn your Windows 7 laptop into a wireless hotspot

Sharing your Windows internet connection via software has traditionally been a tricky business.

There are programs that can help you do it, but they're often awkward to set up, and prone to complicated security and reliability issues, so most people don't even try.

But that could all be about to change, thanks to a new Windows 7 feature called Virtual Wi-Fi.

The idea is a simple one: the operating system can virtualise any compatible wireless adapter, to make it appear as though you've as many additional adapters as you need.

The effect is dramatic. Once it's set up, then any Wi-Fi compatible device that can connect to you - another desktop, laptop, or an iPod Touch, say - will immediately be able to get online, by sharing your internet connection through a duplicate of your wireless adapter.

Getting this working isn't too difficult, either, as long as you can get over the first hurdle: finding a virtual Wi-Fi-compatible driver for your wireless adapter.

Intel's latest 32-bit and 64-bit drivers now include support, as do various others for Atheros, Broadcom, Realtek and other big players, but these don't apply to every chipset. Check the support site for your wireless adapter to see what's available.

If you're in luck and manage to find and install an up-to-date Windows 7 driver for your adapter, then the next step is to set it up, and for that you'll need an elevated command prompt. Click Start, type CMD, right-click the Cmd.exe link and select "Run as Administrator".

Now type the following command:

netsh wlan set hostednetwork mode=allow ssid=MyNet key=MyPassword

and press [Enter]. Replace "MyNet" with the name you'd like to use for your custom network, and "MyPassword" with a password that's a little harder to guess.

Still at the command line, type

netsh wlan start hostednetwork

and press [Enter] to fire up the virtual adapter.

Now click Control Panel > Network and Internet > Network and Sharing Centre > Change Adapter Settings, right-click your internet connection and select Properties. Click the Sharing tab, check "Allow other network users to connect...", choose your virtual Wi-Fi adaptor - and that's it.

 

Employees leave managers, not companies

Today I found out one of my good friends left their position at a well-known technology company that many people would “kill” to work for. I asked him why he left, expecting an answer like “I needed more of a challenge”, or “I outgrew the position and there was nowhere for me to grow”, but instead he said “I couldn’t work with my boss”.

As he said this I thought about all the people leaving their positions because they simply couldn’t work with their manager. The work was stimulating, the team was great but their manager was unbearable to work with. In these situations, what seems to happen is companies lose good employees on a regular basis and all the managers sit around a conference table trying to address employee attrition, developing strategies for employee retention.

Employee retention is a real problem that all managers face. The key to being able to keep the good employees is not so much the salary you offer them or even the actual work, it is more about how you manage them and how they feel working under you as their manager. Do they feel valued within your team? Do you provide them with timely feedback? Do they feel your support as a manager leading their team or company?

Abraham Maslow was an American psychologist who was best known for creating Maslow’s hierarchy of needs which can be seen below.

Source: Diana Vanbrabant

As a manager we are able to affect three levels of needs within this hierarchy – safety, love & belonging and esteem. These 3 levels represents different elements within the workplace. The first level - safety refers to job security, career progression as well as health benefits and perhaps even gym membership. How do your employees feel about their job? Are they constantly afraid of cuts due to the recession? Do they know that as a manager you care about their wellbeing as well as their work?

The next level is love and belonging. People want to feel as if they are making a difference and are part of something bigger. As a manager how you approach giving out tasks, mentoring employees and interacting with them show how much you value their work. It is your duty as a manager to show employees how their work is making a difference and is part of a much larger plan. The worst thing for an employee is for them to think they are just another cog in a machine.

The last level is esteem. This refers to confidence and respect. It is important to manage your staff in terms of how they feel towards the work and to their peers and managers. Respect within the workplace is extremely important and can be the difference between keeping a good employee or losing them. Training and development when necessary is a good way to boost confidence and equip staff with the right skills. Investing in your staff to help them upskill benefits both the company and the employees. Zig Ziglar once said that there was only one thing worse than training (or growing) your staff and having them leave, and that is not training or developing them and having them stay.

A Florida State University (FSU) professor and two of his doctoral students have conducted a study which highlights the impacts of an abusive or poor manager/boss. They surveyed over 700 people who work in a variety of jobs and asked for their opinions of supervisor treatment on the job.

The study revealed these results:

39%: Their supervisor failed to keep promises
37%: Their supervisor failed to give credit when due
31%: Their supervisor gave them the “silent treatment” in the past year.
27%: Their supervisor made negative comments about them to other employees or managers.
24%: Their supervisor invaded their privacy.
23%: Their supervisor blames others to cover up mistakes or minimize embarrassment

Source: Florida State University

These points act as a good checklist to see how you are managing your staff because at the end of the day employees leave managers and bosses, not companies!