Wpf Error 40 Bindingexpression Path Error: Property Not Found on 'Object'

WPF Error 40 BindingExpression path error: property not found on 'object'

I wrote some other SO answer recently about how to read the binding errors so they make more sense. To summarize, add line breaks to your error message on the colons and semi-colons, and read it from the bottom up.

Your error message is:

• System.Windows.Data Error: 40 :
  
  
  • BindingExpression path error: 'ConfigurationModel' property not found on 'object' ''IncrementingTextBox' (Name='video_length_textbox')'.
  • BindingExpression:Path=ConfigurationModel.DontUseSensorLength;
• DataItem='IncrementingTextBox' (Name='video_length_textbox');
• target element is 'IncrementingTextBox' (Name='video_length_textbox');
• target property is 'IsEnabled' (type 'Boolean')

This can be read from the bottom up as:

• The binding failing is the IsEnabled property of an element of type IncrementingTextBox (named video_length_textbox).

• The DataItem (DataContext) of the element is an object of type IncrementingTextBox named video_length_textbox

• The binding expression it is trying to find is ConfigurationModel.DontUseSensorLength

• And the problem the binding is having is that the ConfigurationModel property is not found on the data context object IncrementingTextBox

So your DataContext for "video_length_textbox" is set to itself, and your IncrementingTextBox class does not have a public property called ConfigurationModel

Since I don't see you setting the DataContext for your IncrementingTextBox anywhere in your XAML, check out the code for your IncrementingTextBox class. The most likely case is you are setting the DataContext to itself in either the Constructor

this.DataContext = this;

or the XAML

DataContext="{Binding RelativeSource={RelativeSource Self}}"

How to resolve a Binding Expression Path error in WPF?

These binding errors are not related to your DataGrid.

They indicate that you have 3 TextBoxes somewhere of the names fNameTbx, lNameTbx, and emailTbx. A DataGrid does not generate it's items with a Name property, so it is not the one causing these binding errors.

When trying to read binding errors, it's best to break them up by semi-colons and read them backwards, as demonstrated here.

For example,

System.Windows.Data Error: 40 : BindingExpression path error: 'FirstName' property not found on 'object' ''MainViewModel' (HashCode=55615518)'. BindingExpression:Path=FirstName; DataItem='MainViewModel' (HashCode=55615518); target element is 'TextBox' (Name='fNameTbx'); target property is 'Text' (type 'String')

Can also be read as

• target property is 'Text' (type 'String')
• target element is 'TextBox' (Name='fNameTbx');
• DataItem='MainViewModel' (HashCode=55615518);
• BindingExpression path error: 'FirstName' property not found on 'object' ''MainViewModel' (HashCode=55615518)'. BindingExpression:Path=FirstName;

Meaning somewhere you have

<TextBox Name="fNameTbx" Text="{Binding FirstName}" />

Where the DataContext of this TextBox is of type MainViewModel. And MainViewModel does not have a property of FirstName.

I'd recommend searching your project for those names, or you could use a tool like Snoop to debug databindings and DataContext issues at runtime.

System.Windows.Data Error: 40 : BindingExpression path error: property not found on object

You have used Binding Path CheckforNewHubs but it should be CheckForNewHubs.

WPF/XAML Property not found on 'object'

That is a DataBinding Error

Easiest way to read those is break it up by the colons/semi-colons, and read it backwards

System.Windows.Data Error: 40 : BindingExpression path error: 'Sender'
property not found on 'object' ''Char' (HashCode=6619237)'.
BindingExpression:Path=Sender; DataItem='Char' (HashCode=6619237);
target element is 'TextBlock' (Name=''); target property is 'Text'
(type 'String')

1. target property is 'Text' (type 'String')
2. target element is 'TextBlock' (Name='');
3. BindingExpression:Path=Sender;
4. DataItem='Char' (HashCode=6619237);
5. 'Sender' property not found on 'object' ''Char' (HashCode=6619237)'.
6. BindingExpression path error:
7. System.Windows.Data Error: 40 :

1 tells you that there is a Text property causing the error

2 tells you that the Text property is on a <TextBlock> element

3 tells you the binding express causing the problem is {Binding Path=Sender}

4 tells you the DataItem/DataContext behind the <TextBlock> element is an item of data type Char

5 tells you the actual problem with this: there is no property named Sender on the object of type Char

6 just tells you it's a binding error

7 I have no idea what it means

Since I see you have a public property named Sender on your Message class, and its clear that Message is not Char, its obvious that your DataContext for each item is wrong.

Since it is set to a Char the most likely cause is you are binding to a string, and the DataContext for each element is a character in that string.

And sure enough, ItemsSource="{Binding Source=Messages} means you are changing the binding's Source property from the current DataContext to a string. And strings are just character arrays, so it means you are binding to the character array { M, e, s, s, a, g, e, s }

If you change the Source property to the Path property, then it will correctly read DataContext.Messages instead, and should work.

<ListView ItemsSource="{Binding Path=Messages}" ... />

(The word Path here is optional, since if you don't specify a property name then the binding assumes it is the value for the Path property)

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As a side note, I don't see you setting your DataContext anywhere on the form, and I don't see a public Messages property either.

The MainWindow constructor should probably have a line of code that looks like this to set the DataContext to itself :

this.DataContext = this;

And you probably need a public property for your ObservableCollection<Message> messages so the ListView binding can find it :

public ObservableCollection<Message> Messages
{
    get { return messages; }
    set { messages = value; }
}

I'm not sure if these were merely overlooked, or if you didn't know you needed them.

Oh, and if you plan on changing any of these bound properties and having the UI automatically update, you'll want to implement INotifyPropertyChanged too :)

And since I'm in tutorial-mode here, I figured I should also link to this answer :

Transitioning from Windows Forms to WPF

I would highly recommend reading through it (and the linked articles) if you're new to how WPF works, and are switching from Winforms to WPF. Which it sounds like you are :)

BindingExpression path error

Your DisplayMemberPath binding is causing the error, and in your case should be removed entirely since it is not needed.

To use DisplayMemberPath, you need to be able to reference the property like ListView.ItemsSource[X].SomeProperty, where SomeProperty would be your DisplayMemberPath

You are getting this error because your ItemsSource is a List<String>, and String does not contain a property called CategoryModel.

To explain the exact binding error you have:

System.Windows.Data Error: 40 : BindingExpression path error: 'CategoryModel'
property not found on 'object' ''String' (HashCode=-57655201)'.
BindingExpression:Path=CategoryModel.CategoryList; DataItem='String'
(HashCode=-57655201); target element is 'TextBlock' (Name=''); target property is
'Text' (type 'String')

• This line means it can't find the property CategoryModel on the object String

  BindingExpression path error: 'CategoryModel'
  property not found on 'object' ''String' (HashCode=-57655201)'

• This line contains the Path property for the binding expression that is throwing the error

  BindingExpression:Path=CategoryModel.CategoryList;

• This line tells you the Source object for the binding that is throwing the error (typically the DataContext)

  DataItem='String'
  (HashCode=-57655201);

• And this line means it is failing to bind the property Text on a TextBox (DisplayMemberPath is a shortcut way of making the ItemTemplate a single TextBlock, with it's Text bound to the DisplayMemberPath property)

  target element is 'TextBlock' (Name=''); target property is
  'Text' (type 'String')

So to put it all together, it is telling you that it is trying to bind TextBox.Text to {Binding Path=CategoryModel.CategoryList}, however the DataContext behind the TextBox is of type String, and String does not have a property called CategoryModel

BindingExpression path error: property not found on 'object'

You don't want to set the DataContext on the UserControl. Instead, you want to set it in the scope of the UserControl.

Usually you do this in the constructor of the UserControl. I usually add a line like this:

this.RootElement.DataContext = myData;

Where RootElement is the first sub-element (the Content) of your UserControl (usually a panel like Grid or StackPanel).

In your case it would be:

this.lsvwOutput.DataContext = FindResource("myDataSource");

And makes sure that it's after the InitializeComponent() call.

It's just a question of scoping. You set the datacontext on the root panel of the usercontrol. This is a really non-obvious part of WPF.

UPDATE: As Markus points out below, in the case of a listview, you want to set an array of data, not just a data point. Take that into consideration when setting the DataContext in your constructor.

BindingExpression path error: property not found

In the UserControl definition you have the following line:

DataContext="{Binding RelativeSource={RelativeSource Self}}"

It means that the DataContext for that control is the control itself. So WPF is trying to find the IsProgress property in this control.
As I understand, the IsProgress property is defined in the ViewModel of your Page.

So the best option to fix it is just to remove above line.

Additionaly to fix Width and Height bindings in control add RelativeSource={RelativeSource AncestorType={x:Type UserControl}} to them.

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