WPF Text Box allowing decimal entries - wpf

Question

I am new to WPF (VS2013, .NET Framework 4.5) and what was a big suprise to me is that I can not enter a float value to my text box.
My text box is bound to a float variable. If that variable defaults to say 5, then text box will show 5. But I have an issue:
I can not enter . if I want to have say 5.5. To solve this, I found someone's suggestion to add to xaml for text box binding "StringFormat=N2".
That created even more issues:
1. Now even if I have even number like 5, it shows as 5.00
2. If I put cursor btw 2 zeros or anywhere else, neither backspace nor delete key will delete the entrie
3. If I put cursor btw 5 and . (in 5.00) and type ".10", I end up with 5.10.00.
Is it possible that number entry in WPF is so complicated??? All I want is to enter a number that will be stored in a float.
If I enter 5, it should show as 5 in TextBox.
If I enter 5.05, than that is how it should show in TextBox.
The underlying float variable can hold both 5 and 5.05, both as a float.
UPDATE:
Here is my code
private float age;
public float Age {
get { return age; }
set
{
if (value <= 0 || value > 120)
{
throw new ArgumentException("The age must be between 0 and 120 years");
}
age= value;
}
}
and in XAML:
<TextBox Name="txtAge" Text="{Binding Age, UpdateSourceTrigger=PropertyChanged, StringFormat=N1, ValidatesOnExceptions=True}" />

Answer 1

From Standard Numeric Format Strings
The number is converted to a string of the form "-d,ddd,ddd.ddd…",
where '-' indicates a negative number symbol if required, 'd'
indicates a digit (0-9), ',' indicates a thousand separator between
number groups, and '.' indicates a decimal point symbol.
It would seem that N will include thousands separators.
See also Custom Numeric Format Strings

Answer 2

There is no binding in your code. Note the Path=Age :
<TextBox Grid.Row="0" Text="{Binding Path=Age, UpdateSourceTrigger=PropertyChanged, StringFormat=N1, ValidatesOnExceptions=True}"/>
The binding between the model view with the view model:
var myModel = new ViewModel();
control.DataContext = myModel;
Then the ViewModel (implement the INotifyPropertyChanged interface)
public class ViewModel : INotifyPropertyChanged
{
private float _age;
public float Age
{
get { return _age; }
set
{
if (value.Equals(_age)) return;
_age = value;
OnPropertyChanged("Age");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName = null)
{
var handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}
You should be interested in MVVM literature:
MVVM overview
MVVM by Microsoft Patterns & Practices
As the other answer suggests, you may have a mismatch between what you expect to be the decimal separator (.) and what your system consider as the decimal separator (maybe something else like ,).

Answer 3

I found the solution on this site, the trick is to force the behavior of framework 4
If you still want to use ‘UpdateSourceTrigger = PropertyChanged’, you can force the .NET 4 behavior in your .NET 4.5 application by adding the following line of code to the constructor of your App.xaml.cs:
public App()
{
System.Windows.FrameworkCompatibilityPreferences
.KeepTextBoxDisplaySynchronizedWithTextProperty = false;
}
Source:
http://www.sebastianlux.net/2014/06/21/binding-float-values-to-a-net-4-5-wpf-textbox-using-updatesourcetriggerpropertychanged/