I am interested in binding an object to a RichTextBox so I can append to the object to update the RichTextBox. What class is recommended to be used for the binding? Also, how will myRichTextBox.DataBindings.Add() be used with the recommended class?
I have attempted using string as a data binding, but have failed since it seems that strings cannot be used without using a custom class (C# WinForms databinding RichTextBox.Text to a String).
I have also attempted to use a list of strings through 'myRichTextBox.DataBindings.Add("Text", myListOfStrings, null), but to no avail. I am certain I do not have a clear understanding of the DataMember argument which may be prohibiting me from taking that path.
Related
I know this is a pretty broad problem, so I'm surprised I haven't found a good answer yet. Here's my situation:
I have a class named TimeConverter that I use quite often, which implements the IValueConverter interface converts a string containing an amount of time (such as "25:36") into an integer representing the number of minutes (which for the earlier example would be 1536). Currently, when someone enters something untranslatable (like "asdf") the converter returns DependencyProperty.UnsetValue, which causes the bound element (usually a TextBox) to show a red border. Here's the problem, the class containing the integer property on the other end of the binding needs to know that there is a conversion error.
I've found this to be quite difficult and almost impossible to do without the data item having a reference to the bound TextBox. If I get a reference to the TextBox, I can use the Validation attached properties, but i feel like that's sloppy and its also not always possible. Currently I have one of these bindings in place on a TextBox, inside a Setter, inside a Style, inside a DataTemplate (pretty far removed from the visual tree), which also prevents me from using the Validation.Error even for notification. And of course the simple answer of binding Validation.HasError to the data item doesn't work because of how the property is declared.
So how CAN I notify the data item when the conversion fails?
I am looking to bind a richtextbox's text property to an array or list of custom objects. Is this possible? I see lots of WPF related binding for richtextbox but I am doing this in winforms. My searches for an example article have not turned up anything of value yet. Figured I would ask here.
One of my database calls returns to me a list of specific instructions and I would like to stuff this entire list of instructions into the richtextbox all at once. The text property does not support an IEnumerable type so I am not sure if I can do what I am trying to do or not. I was looking for a method to fill my richtextbox without all the for looping and inserting one item at a time. I figured data binding was the best fit for that.
I've run across the same problem and have solved it by creating a custom ValueConverter. The code for it can be found here.
Basically it takes an IEnumerable in and then returns a string with a custom separator (defaults to NewLine).
I've only scraped the surface of validation in WPF and have come across a scenario that is likely fairly common: I have a TextBox whose value needs to be validated against a variable data type, depending on the context. For example, if the context's data type is 'int,' then the TextBox needs to accept only input that can be converted to an Int32.
My first thought was to inherit from the ValidationRule class and to include the context and to use a switch inside the overridden Validate function, but I am unable to bind anything to it since it is not a FrameworkElement.
Any thoughts?
You can expose IDataErrorInfo. This lets you do data validation with complex logic.
Personally I don't like using IDataErrorInfo for something this simple because it requires a gratuitous creation of a ViewModels and a lot of extra code where none should be necessary. It should be as simple as this:
I have a markup extension that allows me to create a binding with custom validation code specfied as a C# expression. This is extremely simple to do, except for the C# parser: Just implement ProvideValue() by constructing a MultiBinding that uses a converter and builds the appropriate validation structure. This allows the validation expression to receive the containing DataContext and the user-specified Binding object in addition to the value being validated.
With this solution coded, you can do something like this:
BoundProperty="{my:ValidatedBinding
Path=SomeProperty,
ValidationExpression = context is TextBox ? (int)value>3 : (int)value<7,
Mode=TwoWay,
Converter=...
You could easily adapt my solution without the C# parser by creating the expression as a lambda in the code-behind and referencing it with x:Static:
public static reaonly Expression myValidatorExpression =
(object value, object context, BindingBase binding) =>
context is TextBox ? (int)value>3 : (int)value<7;
...
ValidationExpression={x:Static local:MyClass.myValidatorExpression}
In general I find this technique easier and clearer than using ViewModels. I still use ViewModels when there is a complex transformation needed, otherwise just pure XAML straight to the business objects layer.
Note that this approach assumes your business objects layer is not tied to any particular the back-end storage layout (eg SQL table structure). If it were, changing the back-end storage would require changing my UI and this would not be desirable either, so a ViewModel would be desirable from that standpoint. But if not, I always prefer to keep it simple and just use straight XAML.
If i have a Binding which has a property path and the data source can i execute it in code, to find the value?
The path that i am trying to follow can be quite complicated, including collection lookup and multiple levels.
there is a hack :
create a content control
use BindingOperations.SetBinding()
then retrieve the content
is there a better way?
You can avoid using a ContentControl, and write your own very simple class that derives directly from DependencyObject, and provides a single DependencyProperty, which you can then target with the binding. Aside from that, no, there isn't any better way - binding machinery in WPF is very much tied into the concept of dependency properties, and a binding cannot really be a "free-standing expression" that is just evaluated.
I am having a hard time figuring out good reasons for the dependency property. Why the System.Controls.TextBox "Text" property a dependency property and not a normal property? What benefits does it serve being a dependency property?
One of the things I am trying to accomplish is to add a ValidationRules property to my UserControl which will contain other validation rules. Like here:
<customControls:RequiredTextBox.ValidationRules>
<validators:NotNullOrEmptyValidationRule ErrorMessage="FirstName cannot be null or empty"/>
</customControls:RequiredTextBox.ValidationRules>
The problem is that I am not sure if ValidationRules property should be DependencyProperty or just a normal property.
The above code gives the following error:
{"Cannot add element to 'ValidationRules'; the property value is null. Error at object 'LearningWPF.ValidationRules.NotNullOrEmptyValidationRule' in markup file 'LearningWPF;component/addcustomerwindow.xaml' Line 35 Position 66."}
Here is the ValidationRules property:
public static readonly DependencyProperty ValidationRulesProperty =
DependencyProperty.Register("ValidationRules",
typeof (Collection<ValidationRule>), typeof (RequiredTextBox),
new FrameworkPropertyMetadata(null));
public Collection<ValidationRule> ValidationRules
{
get { return (Collection<ValidationRule>)GetValue(ValidationRulesProperty); }
set { SetValue(ValidationRulesProperty, value); }
}
The benefits are primarily two fold:
Firstly a dependency property is only created when it is used, this means the TextBox class can be very efficient, with a low memory footprint since it has a minimal number of real properties taking up space on the heap. This is especially important in WPF where all controls are just collections of more and more specific types. If each of those inner types declared tens of properties to define behaviour and look then a high level control like a button would end up having the size of a class with something in the ballpark of a hundred properties.
Secondly dependency properties can be tied to an object other than the type that they are created for. This allows the case where a control can set a Grid.Column property, which the Grid control can read and use for layout. This means that we don't hundreds of decorator classes supplying tiny pieces of functionality required by other controls. This means that xmal is far more intuitive and readable.
Edited to address the example in your revised question:
While your validation property won't gain much benefit from being a dependency property (basically out of the reasons in all the answers so far I can only really see my comment of memory footprint coming in to play), and it certainly isn't advantageous as it is in the case of the Text property of a text box where you may want to bind it, or change it based on some other input, I would still implement it as a dependency property. My reasoning for this is simple; you don't gain much, but it also doesn't cost you anything - I have never wished I had used a basic property in a custom control whereas when I first started writing them I was constantly upgrading my basic properties to dependencies because I wanted some extra functionality.
Simply put, while the dependency property is more complex to define that a normal property I would still use it as the de facto standard for WPF controls unless there was some good reason to do otherwise. In much the same way as a property is the standard for classes, even though a field is easier to implement.
The primary benefits I would say are:
First-class data binding support.
Clean Attached Property semantics
Property values which "depend".
That last point is key
Before Dependency Properties, having a value have a local value, an animatable value, an overridable value, a styleable value, a templatable value would require the declaration of multiple Properties/Fields/Dictionary entries, as well as complex state+precedence management.
Dependency Properties give you all these features out of the box, while declaring just ONE property.
That being said, in your case, you may not want to declare your ValidationRules as a DependencyProperty if you won't need to take advantage of these features.
If you do, you'll want to have different handling for your collections (non-empty collections for example). In this particular example, I would use Reflector and see how the .NET TextBox implements their validation collections, and see if you can reuse or copy the code.
There's no point re-inventing the wheel unless you're certain your wheel will be better. My personal experience is that my reinvented wheels tend to be missing things ;).
As Martin Harris already pointed out, DependencyProperties can limit the memory footprint by throwing the property values into a dictionary, however this can (and I believe was?) done by MSFT before the advent of DependencyProperties.
Martin also mentions Attached Properties, but those were also available (at least in designer) before the advent of DependencyProperties. The Attached Property implementation using DependencyProperties is much cleaner.
Dependency Properties are required if you want to use binding to populate the value of a property. If it was just a normal property, you wouldn't be able to bind the Text property to a property of your View Model object, for example.