We're planning to create a web application where users can build custom "forms," choosing which fields they would like, and how the data in those fields should be represented. Users can then fill out these forms in a DetailsView-like control, thereby creating "documents." The documents can be shown in a DetailsView, or certain fields of several of them can be shown in a GridView. At least, that's the idea.
The problem is that GridView and DetailsView seem to be specifically designed to access Properties on objects that come out of a DataSource. Since we want to have completely arbitrary forms, we can't restrict ourselves to building a class with Properties to represent each field. We have to be able to have any number of dynamically-specified fields on a form.
Is there any way to leverage the existing controls so we don't have to re-implement paging, sorting, and all the other things that GridViews are already set up to do, or will I just have to create my own GridView-like control from scratch?
Edit:
More specifically, the difficulty I am having is in getting inline editing to work on the GridView. For example, let's say that one of the "fields" that is added to a "form" is a calendar field, which should display a date as text in read-only mode, and display a calendar control in edit mode. When the "save" button is clicked, the date selected by the calendar control needs to be saved to the database as the new value for the given field of the given document (i.e. instance of the form). My initial idea was to create a special DataControlField class which, given a form field key, would know how to databind thusly:
FormDocument doc = DataBinder.GetDataItem(cell) as FormDocument;
FormFieldValue fieldValue = doc.FieldValues[FieldKey];
fieldValue.AddReadOnlyControls(cell);
... instead of:
Object dataObject = DataBinder.GetDataItem(cell);
cell.Text = DataBinder.GetPropertyValue(dataItem, FieldKey);
This would probably work for displaying the field values, but if the user tries to edit and save one of the FormDocuments I don't know how I would convince the GridView to do something like this:
doc.FieldValues[FieldKey] = newValue;
Currently, the API for DataControlField uses the ExtractValuesFromCell method to put the property name and value into an IOrderedDictionary. Those values are then applied to the given properties of the objects in the GridView's databound IEnumerable. The problem is, I can't work with properties of an object because in this case the object needs to have a completely arbitrary number of fields.
A GridView can be bound to any object that implements IEnumerable. The advantage of using one of the xDataSource controls is that it can implement paging and sorting for you without any additional code, but you certainly aren't tied to them.
If I understand your question correctly, you do not know the number of columns to display in the GridView until runtime. In that case, I would recommend building an array from your form data and binding the grid to that. You will have to implement paging and sorting yourself.
The DetailsView is not very customizable so you should take a look at the FormView. However, I think you are going to end up dynamically adding controls to whatever container you use.
What you need is totally dynamic GridView. I quess you would have to extend it with the controls ( functionalities ) in your description
Here's what I ended up doing:
I created a new data type that contained a Dictionary of answers, indexed by Field ID.
I created a new type of DataControlField with a FieldId property, which retrieves the proper answer value for that FieldId from the Dictionary mentioned above.
I added data type and data keys properties to this custom DataControlField and overrode the ExtractValuesFromCell method so that it could create a new instance of the answer class and add those values to a Dictionary, which was stored under the property name by which that dictionary would be found in the new data type mentioned in step 1.
I used my own GridView class, used the .NET Reflector to see how the normal GridView calls the ExtractValuesFromCell method, and then changed that so that it would pass the same Dictionary object in to each DataControlField. This way, each field could add to the same Dictionary, rather than replacing the Dictionary that the last one had added under the same property name.
I used a DataFieldGenerator to generate the one of my custom DataControlFields for every field associated with a given form, and I told the GridView to use that DataFieldGenerator to auto-generate its fields.
I set up my ObjectDataSource so that it would know how to save all the answer values from an object of the type mentioned in step 1.
It was tricky, but worthwhile.
Related
I'm using Visual Studio 2010 to create a dynamic data site with scaffolding according to: http://www.asp.net/web-forms/videos/aspnet-dynamic-data/your-first-scaffold-and-what-is-dynamic-data
The site displays a SQL table with an "Insert New Item" link, which takes you here:
I have another SQL table which holds some of the information already. I would like to add a function that is called when the user navigates away from the "account" field; the function will query the other SQL table and populate the fields that it already holds for that account.
I'm stuck on where to put the function and how to setup the account field to call it.
It's a couple of years since I did one of these so pardon the details being a bit short.
You can 'override' the default New Item form. In that you can pre-populate the fields with anything you want. I think you have to take care of the Save also, and of setting out the controls on the form and populating them (you've overridden the generated form after all).
Another possibility is to create a partial class which extends the Model class and populates it in a constructor extension (I remember doing various stuff with this technique). There might also be some extension points on the model Context (or whatever its called) which you can tap into - it's pretty flexible as I remember.
Depending multiple choices done by a user in few steps I have to generate a form in a web page for the user.
In a database I had all the necessary stuff (regex validation of every form field, name, type etc.) I would like to know what could be the best way to autogenerate a form using MVC3.
Should I autogenerate a model, set the model of my views to dynamic, and inject some validation attributes to every property of my dynamic model?
How should I get the values on my post action?
As the fields are all dynamic (from the database), your model could very easily store an IEnumerable where Question is an object which has information about the type of field. i.e. Id, TypeId (text, checkbox, select list), Wording, Heading, ValidationTypeId etc.
Then use mvchelpers passing in Question to a method which would determine the html to output. This could very well include a validator.
On the form loop over Model.SurveyQuestions and for each row send Question to the mvc helper. The helper, knowing everything about the Question can output the label, type of input box and the required validator.
This is a wise way to accomplish what you are trying to do as your input fields is dynamic. I just completed a project doing exactly this.
I have a classic ObjectDataSource and a ListView in my page. The List view just displays some data and when switched to edit template it allows the user to change the values. I want the user to edit just some values -- so I bind just these ones in the edit template.
The problem is that the other values suddenly turn to nulls or 0. I tried to bind all of the values at once and it works fine, but I cannot understand why the old/original values just disappear. Is there any way how to bind the old values?
Thanks for help.
The problem is, that only the data that is included into a round-trip to the server will be available in the postback. That includes all that that is bound to BoundFields, TemplateFields or if the Propertyname is included in the DataKey (or DataKeyNames, don't know right now).
The best approach to fix this, and to keep the overhead to a minimum is to add your primary key to the DataKeyNames collection. This allows you to have access to your custom object that contains an unique identifier and all properties that have just changes.
In your Update Method of the ODS (in your custom class) you now need to retrieve the old object by its unique identifier, manually assign the new values and saves your object back to the database
I have a form with 30 fields of data on it - mostly TextBox controls displaying string data, but there are 3 dropdownlist comboboxes and one textbox used to display a datetime. I'm using a BindingSource to bind these fields to a custom data object derived from BindingList<>.
Depending on the content of the data in the data source, sometimes a specific field will simply fail to bind - meaning the data from the data source does not get moved to the control. The control that fails is a simple textbox.text / string binding.
I can perform a specific query that in every instance will cause this specific field to fail to bind. I have other queries that can be performed that produce a set of data where the bindings all work perfectly.
My question is - what causes data binding to fail? Will the failure of some other bound field stop all the other bindings from firing?
Here are a few things that you could check
Is there a mismatch in the size of the data field and the field in the UI
Are there any special characters in the data
Is the code that binds the fields not being run in certain circumstances
Is there some code that is clearing the binding
I solved this issue by writing my own binding infrastructure. That gave me more explicit control over when bindings fired and what happened as a result.
Often I need to combine data from multiple tables and display the result in a GridView control.
I can write a Linq query inline in the Page_load event, return an anonymous type that combines all the fields that I need, and databind the result to the GridView control.
Problem: I use 'helper methods' as described by Scott Guthrie on his blog. Such a helper method cannot return an anonymous type. The query would have to be inline for this approach.
I can write a database view that returns the data that I need, and write a helper method with a query against this (new and known) type that it returns.
Problem: I will need a lot of views in my database schema, and I will introduce a lot of redundant aspects of my data. I also lose some of the advantage of using Linq - removing all business logic from the database.
I would like to take an approach that lets me keep the Linq queries in helper methods, yet allows me to access all the attributes that I need on the grid in their respective databinding expressions. Can this be done?
I asked the wrong question, as I frequently do. What prompted me to look into anonymous types was an apparent limitation of the GridView - my inability to use a databinding expression in an <asp:BoundField> (the DataField parameter only accepts column names of the table that the Linq query pulls in).
Turns out that in a TemplateField it is possible to use Eval and access members of the Linq data item, and Linq takes care of the query for me.
In other words, I can keep the query in my helper method, have it return a primary database table type (e.g. Account), and I bind the Accounts to the GridView.
In the databinding expressions I can access data members of the Account objects that reside in other tables, without having to explicitly pull them in in the query. Perfect.
I don't know if there is a viable way to achieve this using anonymous types. But I have a suggestion that will work in WinForms, but I am not sure about ASP.NET.
What you need is a type with properties where neither the number of properties, nor the types and names of the properties are known at compile time. One way to create such a thing is ICustomTypeDescriptor.
You have to create a type implementing this interface with an private backing store of objects backing the properties returned by the query for one row from the query. Then you implement GetProperties() to return one PropertyDescriptor per column and PropertyDescriptor.GetValue() and PropertyDescriptor.SetValue() to access the backing array.
By implementing PropertyDescriptor.Name you will get the correct column name; this will probably require another backing store storing the property names. And there is a lot more to implement, but in the end your new type will behave almost like a normal type - and now the if - if the control you are binding to knows about and uses ICustomTypeDescriptor.
UPDATE
I just found an bit of text stating that ASP.NET data binding knows and uses ICustomTypeDescriptor.
Scott's earlier post in the series talks about shaping the result set before inserting into a grid:
Part 3 - Querying our Database
Scroll down to "Shaping our Query Results".