I'm new to c# and I'm looking for a way to bind a property of an object of my own to the value of a textbox in a regular form (reset the property of the object everytime the value of the input changes).
I have read some information and it seems that this can be done only for database objects. Can you give me additional information.
Assuming you mean Windows Forms textbox,
say
textBox.DataBindings.Add("Text", obj, "SomeProperty");
whenever you feel like binding it. Bindings are usually done in Form_Load event handler, if the object can be obtained at that time of course, and if there's no complex logic with different data sources.
Note that this will only work in one direction (changing TextBox will yield object property changes). To sync the other way round, the object must implement INotifyPropertyChanged interface.
If you want to persist the information between runs of the application (i.e. have it be saved when you close the app and re-appear when it opens), it's easiest to use the Windows Forms designer (I assume you are coding a WinForms app) to bind the value of the TextBox to an application setting. (This article on validation provides a screenshot similar to what you want.) (EDIT: Here is the exceptional article on the subject: Exploring Secrets of Persistent Application Settings. And here is a snippet page that I put together to discuss binding.)
This binding is automatically two-way, unlike the binding that #gaearon mentions. You just need to make sure that you save the settings (i.e. Properties.Settings.Default.Save()) before closing the application (e.g. as the event handler for the Form.Closing event).
If you need more clarification, leave a comment.
Related
I frequently have the following task:
I have a collection of objects (f.e. Customers) and want to provide the user with an editor for these objects. Typically I have some list control on the left side of the editor and a form on the right side. The form displays the properties of the object that is currently selected on the left side.
Regarding the confirmation of any changes, there are at least two strategies:
make the editor a modal dialog window and give it OK/Cancel buttons. On OK save all changes for all objects
give the editor a Save button above or below the form on the right side that would allow the user to confirm changes to the currently selected object.
My question is about the second strategy, implemented as an MVVM application with WPF:
I would like to give my user a feedback that there are unsaved changes. Applications like text editors often solve this by enabling the Save button when any changes occurred and disabling it again once the user pressed it to confirm her/his changes.
If I understand correctly I would have to monitor changes to any bound properties in my form (backed by a model class). Usually my model classes use auto properties (no explicit getters and setters). Do I have to write explicit getters for all my properties to enable the Save button when anything changed, or is there a smarter way to achieve this?
Following the MVVM pattern, your ViewModels should implement INotifyPropertyChanged interface, than you can easily subscribe to PropertyChanged event and monitor properties changes
If you don't want to write INPC aware getters and setters in your model classes, then another way is to write a equality compare method instead, and then have your save command availability callback call into that to compare the "live" object with the edited one. I'm assuming you have a cloned object that is being edited in order to rollback if the user chooses not to save.
WPF will call it automatically as the user clicks around and types, or you can give it a hint with CommandManager.InvalidateRequerySuggested()
In Flex (AS3) you can do neat things where you bind a property to an expression/variable/object. e.g. button.enabled = {!obj.name.empty} It makes for very neat GUI validation amongst other things.
I don't see any such facility in Visual Studio GUI designer but wondered if this sort of functionality exists in .Net/C# and if so, to what extent?
I don't see any such facility in Visual Studio GUI designer
In fact there is. Select the form/control in the designer, then go to Properties window and expand the (DataBindings) category. You'll see a couple properties there, and more if you click the (Advanced) item.
to what extent?
It could only bind to a property (no expressions are supported). To make it work, the object providing the property must support property change notification. The standard way is implementing INotifyPropertyChanged interface, but there are also other mechanisms - IBindingListimplementation providing ListChanged event, object providing event named PropertyNameChanged for a PropertyName etc.
As I mentioned, standartly you can bind only to properties. However, at runtime with some helpers you can really bind to a method or expression. I've already provided examples of doing that in the following threads Button enable and disable on text changed event, Exchange UserControls on a Form with data-binding, Custom WinForms data binding with converter not working on nullable type (double?), .Net WinForms design to sync Data and Controls for a single item data binding, and my own question Cross tabular data binding in WPF for more complex scenarios.
Contrary to what some WPF-ers say, there are no WF limits when binding to a custom objects/collections. The only limits are when binding to other control properties because control property notification pattern is not strictly followed like in WPF where it is by design.
I’m trying to add a honey pot field to our contact us form. When I add hidden field to the form via the Kentico GUI (with conditions making it invisible) it’s not available in the source so I don’t think it will actually work. However I also tried adding the form via the GUI and trying modify the style on prerender in my form control won’t work either (Code below). It is odd as it will actually let me change the value of the field in my form control but not the styling. Is this typical of Kentico and is there a solution to trying to implement a honeypot field? I had suggested we just add more validation methods to the form, but I was told that they want the same behavior as the existing forms.
Here is the method I’m using.
((CMS.FormControls.EditingFormControl)viewBiz.BasicForm.FieldEditingControls["Pooh"]).Style.Add("display", "none");
Thanks
Under the advanced properties of the field input, you should be able to apply styles to the input. You could set display:none; there to hide it from the user, but still have it available in the source.
I'm also going to create a form control for this so that it can easily be applied to another with some validation functionality (i.e. a redirect to captcha)
C# How do I use an even to get my GUI update on change of an object?
I have a GUI program that creates an object and displays the object in a data grid through reflection.
When the user updates the information I want to be able to verify the new information and send feedback to the user. I have a method that does the verification of the information, I just need to figure out how to update the GUI with the new information.
thx.
Another general approach would be to support IObservable on your object, and IObserver on any classes (such as user interface elements) that wish to be notified of changes to your object. You can have any number of observers of changes on your object. It's a little more work than the "out of the box" data binding on controls such as data grids, but I would say more flexible.
Perhaps you could be more specific or show some code, but check that each Column Object of the .Net Datagrid has a property named DataPropertyName, which binds by reflection to the property of your objects, it should work..
Other thing is to implement the INotifyPropertyChanged on your objects, and Refresh the Grid on the PropertyChanged event.
I have a MVVM (Prism) application that I need to implement a master details screen wheer the master is a listview and the details is displayed next to it. Read-only seems easy enough (haven't done it yet but I've got my head around WPF binding) but edit/add confuses me.
How to I make it so the master is not updated until the details is saved?
How do I make it so you can't change the master's current selection while in edit/add mode?
I've been googling a plenty but have not found any meaty examples of this.
Thanks.
PS: This view is a child view on a larger screen. This is why I want both master and detail together.
You certainly can do this, though in my opinion such a UI design fails to harness the full power of WPF. Old WinForms UIs usually didn't update most of the application until data was saved to SQL Server (or wherever) because they didn't have real business objects and a powerful binding system like WPF. Trying to copy WinForms limitations within WPF seems like a step backward to me. Why not show the latest data everywhere it is visible in the UI, including in the master view? Also, why not allow the user to edit multiple items before saving, for example marking any edited but unsaved item with an animated marker in the master view? Combine these with a generalized undo and you have a better design and more intuitive for the user.
However if your business requirements make it absolutely necessary, here is how to do it:
Preventing changes to data from being visible outside the detail until it is saved
Upon entry into your "edit/add mode", make a copy of the data objects and set your detail view's DataContext to the copy instead of the live object. When the data is "saved", copy the data from the shadow copy back into the live object and set your detail view's DataContext back where it should be.
Preventing the master's current selection from changing while in edit/add mode
Two possibilities:
During edit/add mode, change the master view to disallow mouse hit testing or keyboard focus
When edit/add mode begins, capture the "current selection" then add an event handler that watches for "current selection" changes and immediately changes the selection back to what it was. When edit/add mode ends, remove the handler. This handler can be conveniently coded using a lambda expression and using a closure on a local variable to store the current selection.
Thanks for the answer. Now I've re-read my message, I see it is rather vague. I have a screen that edits an object which contains multiple lists of other child objects. I've implemented these as different tabs in a tab control. One of these tabs edits the comments, so I wanted to display a list of comments with an edit panel for the current selection next to the list. The user could then use add, edit or delete buttons to update the list. I wanted to do this in a pure(ish) MVVM way.
I came up with the following design which seems to work with minimal hacks.
The View includes a list of the child objects simply as a ListView bound to an observable collection within the ViewModel. I included a child object buffer – this is used to buffer changes until they are ready to be saved back to the list (or thrown away).
The View also includes an edit panel bound to the buffer object in the ViewModel. The buffer is updated whenever the list view’s current selection changes using a deep copy. I tried using data binding on the Selecteditem property but the set was never called, so a small code-behind method was added to force the property to be updated when the selection was changed.
The list view and edit view are mutually exclusive. In theory you could hide the disabled one, perhaps using a flip screen. As a general pattern, it is better for my app to have both visible at the same time as the edit panel may show extra information not shown in the list view. The choice as to which panel is enabled is controlled by binding IsEnabled to a ViewModel property like IsEditCommentMode.
Commands to manage the list have to be added, these are New, Editand Delete. Note that Add and Edit will set set up the buffer then set IsEditCommentMode to true. These list management commands are only available when IsEditCommentMode is false.
The edit panel implements Save and Cancel commands, they are only be enabled when IsEditCommentMode is true. When Save is executed, it should copy from the buffer to the list (either add or update) and fire the change notification. Finally, it should set IsEditCommentMode to false.
This all works well and does not seem to violate any MVVM tenents (in my humble but often flawed opinion).