A question that is asked a lot on the Dynamic Data Forum is how can I get a reference to a FieldTemplate, the reason people ask this is because they are used to doing things this was from classic ASP.Net code; the problem with this is that it leads to specialised code in the page, which means custom page and I always go for custom FieldTemplate over custom page.
The problem with most of the custom FieldTemplates I’ve written for production code is that they are not generic which can be ok, but I tend to find myself writing the same sort of things again and again. So with question on the Dynamic Data Forum and on this blog I thought I’d tackle one of these types of problem in a more generic reusable way. This solution come from the previous cascading articles I’ve culminating with Cascading Filters and Fields – Dynamic Data Entity Framework Version which allows fields and filters to cascade. Here I’m going to use the same event model so one control can alert other controls to a change in it’s state thus facilitating say a checkbox hiding or disabling other field on the form depending upon its state. In this article I’m going to look at Checkbox as parent controls enabling other controls to change there status.
What we will need to Build This.
- Event Interface
- Event Delegate
- EventArgs
- Implementations
The Code
Here I will quickly layout the code (each listing is fully commented) we are going to use it is not majorly different form the Cascading FieldTemplate mentioned here
/// <summary>
/// The interface for parent controls to implement.
/// </summary>
public interface IChangeNotifyingFieldTemplate
{
/// <summary>
/// Gets the parent column.
/// </summary>
/// <value>The parent column.</value>
MetaColumn ParentColumn { get;}
/// <summary>
/// Gets the state.
/// </summary>
/// <value>The state.</value>
String State { get; }
/// <summary>
/// Occurs when [state changed].
/// </summary>
event ChangingAwareEventHandler StateChanged;
}
Listing 1 – the IChangingAware event interface
In Listing 1 we have our interface which has an event and three properties we will need top implement in our FieldTemplates. Now we will need a way of sending the current status of the parent control to the child control for this will will use an EventArgs class.
/// <summary>
/// Event Arguments for Changing Aware Event
/// </summary>
public class ChangingAwareEventArgs : EventArgs
{
/// <summary>
/// Custom event arguments for SelectionChanged
/// event of the ParentChangingAwareFieldTemplate control
/// </summary>
/// <param name="value">
/// The value of the currently selected
/// value of the parent control
/// </param>
public ChangingAwareEventArgs(String state)
{
State = state;
}
/// <summary>
/// The values from the control of the parent control
/// </summary>
public String State { get; set; }
}
Listing 2 – Changing Aware EventArgs
As you can see in Listing 2 Changing Aware EventArgs has only one property which is a string for simplicity. We will use Value to pass the current value of the parent control to the child.
/// <summary>
/// Delegate for the changing aware Interface
/// </summary>
/// <param name="sender">Parent Control</param>
/// <param name="e">An instance of the ChangingAwareEventArgs</param>
public delegate void ChangingAwareEventHandler(
object sender,
ChangingAwareEventArgs e);
Listing 3 – The delegate for our parent and child controls
In Listing 3 you can see the delegate for our controls event.
public class ParentChangeNotifyingFieldTemplate
: FieldTemplateUserControl, IChangeNotifyingFieldTemplate
{
/// <summary>
/// Gets or sets the value.
/// </summary>
/// <value>The state.</value>
public virtual String State { get; private set; }
/// <summary>
/// Gets or sets the parent column.
/// </summary>
/// <value>The parent column.</value>
public MetaColumn ParentColumn { get; private set; }
/// <summary>
/// publish event.
/// </summary>
public event ChangingAwareEventHandler StateChanged;
/// <summary>
/// Raises the <see cref="E:System.Web.UI.Control.Init"/> event.
/// </summary>
/// <param name="e">
/// An <see cref="T:System.EventArgs"/>
/// object that contains the event data.
/// </param>
protected override void OnInit(EventArgs e)
{
ParentColumn = Column;
base.OnInit(e);
}
/// <summary>
/// Raises the event checking first that an event if hooked up
/// </summary>
/// <param name="value">The value of the currently selected item</param>
public void RaiseStatusChanged(String value)
{
// make sure we have a handler attached
if (StateChanged != null)
{
//raise event
StateChanged(this, new ChangingAwareEventArgs(value));
}
}
}
Listing 4 – Parent Change Notifying FieldTemplate
In Listing 4 the control that parent FieldTemplate will inherit so that they can generate events for the child control to subscribe to.
public class ChildChangingAwareFieldTemplate : FieldTemplateUserControl
{
/// <summary>
/// Gets or sets the parent column.
/// </summary>
/// <value>The parent column.</value>
public MetaColumn ParentColumn { get; private set; }
/// <summary>
/// Gets or sets the parent control.
/// </summary>
/// <value>The parent control.</value>
public IChangeNotifyingFieldTemplate ParentControl { get; set; }
/// <summary>
/// Raises the <see cref="E:System.Web.UI.Control.Init"/> event.
/// </summary>
/// <param name="e">An <see cref="T:System.EventArgs"/> object that contains the event data.</param>
protected override void OnInit(EventArgs e)
{
// get the parent column
var parentColumn = Column.GetAttributeOrDefault<ChangingAwareAttribute>().ParentColumn;
if (!String.IsNullOrEmpty(parentColumn))
ParentColumn = Column.Table.GetColumn(parentColumn) as MetaColumn;
// get parent field (note you must specify the container control type in
// DetailsView and FormView = CompositeDataBoundControl : DataBoundControl
// ListView = DataBoundControl
if (ParentColumn != null)
ParentControl = GetParentControl();
// finally call base
base.OnInit(e);
}
/// <summary>
/// Gets the Parent control in a cascade of controls
/// </summary>
/// <param name="column"></param>
/// <returns></returns>
private IChangeNotifyingFieldTemplate GetParentControl()
{
if (ParentColumn != null)
{
// get value of dev ddl (Community)
var parentDataControl = this.GetContainerControl<DataBoundControl>();
// Get Parent FieldTemplate
var parentDynamicControl = parentDataControl
.FindDynamicControlRecursive(ParentColumn.Name)
as DynamicControl;
// extract the parent control from the DynamicControl
IChangeNotifyingFieldTemplate parentControl = null;
if (parentDynamicControl != null)
parentControl = parentDynamicControl.Controls[0] as IChangeNotifyingFieldTemplate;
return parentControl;
}
return null;
}
}
Listing 5 – Child Changing Aware FieldTemplate
And Listing 5 is the control that child FieldTemplates will inherit, so it can subscribe to events from the parent control. It contains the logic to find the parent control and a couple of properties to hold the parent column and controls in.
/// <summary>
/// Get the attribute or a default instance of the attribute
/// if the Column attribute do not contain the attribute
/// </summary>
/// <typeparam name="T">
/// Attribute type
/// </typeparam>
/// <param name="table">
/// Column to search for the attribute on.
/// </param>
/// <returns>
/// The found attribute or a default
/// instance of the attribute of type T
/// </returns>
public static T GetAttributeOrDefault<T>(this MetaColumn column) where T : Attribute, new()
{
return column.Attributes.OfType<T>().DefaultIfEmpty(new T()).FirstOrDefault();
}
Listing 6 – Get attribute extension method
The extension method in Listing 6 is there to simplify the code for getting an attribute which we do a lot in Dynamic Data.
/// <summary>
/// Get the DynamicControl by searching recursively for it by DataField.
/// </summary>
/// <param name="Root">The control to start the search at.</param>
/// <param name="Id">The DataField of the control to find</param>
/// <returns>The found control or NULL if not found</returns>
/// public static Control FindDynamicControlRecursive<T>(this Control root, string dataField) where T : Control
public static Control FindDynamicControlRecursive(this Control root, string dataField)
{
var dc = root as DynamicControl; //Category
if (dc != null)
{
if (String.Compare(dc.DataField, dataField, true) == 0)
return dc;
}
foreach (Control Ctl in root.Controls)
{
Control FoundCtl = FindDynamicControlRecursive(Ctl, dataField);
if (FoundCtl != null)
return FoundCtl;
}
return null;
}
/// <summary>
/// Get the Data Control containing the FiledTemplate
/// usually a DetailsView or FormView
/// </summary>
/// <param name="control">
/// Use the current field template as a starting point
/// </param>
/// <returns>
/// A FilterRepeater the control that
/// contains the current control
/// </returns>
public static T GetContainerControl<T>(this Control control) where T : Control
{
var parentControl = control.Parent;
while (parentControl != null)
{
var p = parentControl as T;
if (p != null)
return p;
else
parentControl = parentControl.Parent;
}
return null;
}
Listing 7 – A group of extension methods to get the parent control
Listing 7 is the two extension methods used by the child control to find the parent, by first using GetContainerControl to find the DetailsView, FormView or GridView etc.
!Important:
ALL previous Cascading examples have a minor flaw/bug/feature. The issue occurs when the parent control appears in the list of controls after the child control, which means in the controls OnInit event all following controls are not in the list. There are two options here
- Force the order of columns shown in the data control
- let each child control capture the OnDataBound event of the container DataControl and then find the parent control there, which may be too late to hookup the event
In this article we are going to use the first method and so I will introduce a field generator and an attribute to set the column order.
/// <summary>
/// Allows to specify the ordering of columns. Columns are will
/// be sorted in increasing order based on the Order value. Columns without
/// this attribute have a default Order of 0. Negative values are
/// allowed and can be used to place a column before all other columns.
/// unashamedly nicked from the DD Futures project :D
/// </summary>
[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field,
Inherited = true,
AllowMultiple = false)]
public class ColumnOrderAttribute : Attribute, IComparable
{
public static ColumnOrderAttribute Default = new ColumnOrderAttribute(0);
public ColumnOrderAttribute(int order)
{
Order = order;
}
/// <summary>
/// The ordering of a column. Can be negative.
/// </summary>
public int Order { get; private set; }
public int ListOrder { get; set; }
#region IComparable Members
public int CompareTo(object obj)
{
return Order - ((ColumnOrderAttribute)obj).Order;
}
#endregion
}
public static partial class HelperExtansionMethods
{
public static ColumnOrderAttribute GetColumnOrdering(this MetaColumn column)
{
return column.Attributes.OfType<ColumnOrderAttribute>()
.DefaultIfEmpty(ColumnOrderAttribute.Default).First();
}
}
Listing 8 – Column Order attribute
/// <summary>
/// Implements the IAutoFieldGenerator interface and
/// supports advanced scenarios such as declarative
/// column ordering, workaround for attribute
/// localization issues.
/// Again mostly swiped from DD Futures
/// </summary>
public class AdvancedFieldGenerator : IAutoFieldGenerator
{
private MetaTable _table;
private bool _multiItemMode;
/// <summary>
/// Allows to explicitly declare which columns should be skipped
/// </summary>
public List<MetaColumn> SkipList
{
get;
set;
}
/// <summary>
/// Creates a new AdvancedFieldGenerator.
/// </summary>
/// <param name="table">The table this class generates fields for.</param>
/// <param name="multiItemMode"><value>true</value> to indicate a multi-item control such as GridView, <value>false</value> for a single-item control such as DetailsView.</param>
public AdvancedFieldGenerator(MetaTable table, bool multiItemMode)
{
if (table == null)
{
throw new ArgumentNullException("table");
}
_table = table;
_multiItemMode = multiItemMode;
SkipList = new List<MetaColumn>();
}
private bool IncludeField(MetaColumn column)
{
// Skip columns that should not be scaffolded
if (!column.GetScaffold())
return false;
// Don't display long strings in controls that show multiple items
if (column.IsLongString && _multiItemMode)
return false;
// Skip columns that are on the skip list
if (SkipList.Contains(column))
return false;
return true;
}
private ColumnOrderAttribute ColumnOrdering(MetaColumn column)
{
return column.Attributes.OfType<ColumnOrderAttribute>().DefaultIfEmpty(ColumnOrderAttribute.Default).First();
}
#region IAutoFieldGenerator Members
public ICollection GenerateFields(Control control)
{
// Get all of table's columns, take only the ones that should be automatically included in a fields collection,
// sort the result by the ColumnOrderAttribute, and for each column create a DynamicField
var fields = from column in _table.Columns
where IncludeField(column)
orderby ColumnOrdering(column)
select new DynamicField()
{
DataField = column.Name,
HeaderText = column.DisplayName
};
return fields.ToList();
}
#endregion
}
public static partial class HelperExtansionMethods
{
/// <summary>
/// Gets a value indicating if the column should be scaffolded. This honors the
/// ScaffoldColumnAttribute as well as returns true if the column is an enumerated type.
/// </summary>
/// <param name="column"></param>
/// <returns></returns>
public static bool GetScaffold(this MetaColumn column)
{
// make sure we honor the ScaffoldColumnAttribute. The framework already does this
// but we want to do this again as the first thing.
var scaffoldAttribute = column.GetAttribute<ScaffoldColumnAttribute>();
if (scaffoldAttribute != null)
return scaffoldAttribute.Scaffold;
// always return true for enumerated types
return column.ColumnType.IsEnum || column.Scaffold;
}
}
Listing 9 – The IAutoFieldGenerator
I have included Listing 8 & 9 for completeness they can both be found in the ASP.NET July 2007 Futures Source Code project on Codeplex and all I’m going to do is add [ColumnOrder(-1)] to the Discontinued column of the Products table (-1 is before zero and the default value is zero).
So now we are ready to setup some FieldTemplates to act as parents and children. Here we will create on parent control by modifying the default Boolean FieldTemplate Boolean_Edit.ascx.
Implementing the above classes in the FieldTemplates
Here we have a class for parent FieldTemplates to inherit and one for children, the parent exposes two properties and an event and the child class does the dirty business of finding the parent control.
Here we are going to use the Boolean_Edit.ascx for as out parent, you could use any theoretically but I thought Boolean made for a good sample.
#region Changing Aware code
/// <summary>
/// override the Value property and
/// return the controls curretn state
/// </summary>
public override string State
{
get
{
return CheckBox1.Checked.ToString();
}
}
public MetaColumn ChildColumn { get { return Column; } }
protected void CheckBox1_CheckedChanged(object sender, EventArgs e)
{
RaiseStatusChanged(this.CheckBox1.Checked.ToString());
}
#endregion
Listing 10 – code to add to the parent control (Boolean_Edit.ascx)
You just need to add the code from Listing 10 to the Boolean_Edit.ascx.cs file and then change the classes inheritance to ParentChangeNotifyingFieldTemplate now Boolean_Edit FieldTemplate is publishing its ChangingAware event.
#region Changing Aware Control
// added page init to hookup the event handler
protected override void OnDataBinding(EventArgs e)
{
// get the parent column
var parentColumn = Column.GetAttributeOrDefault<ChangingAwareAttribute>().ParentColumn;
if (!String.IsNullOrEmpty(parentColumn))
{
//TODO: get the value from Row of the ParentColumn
Object value = DataBinder.GetPropertyValue(Row, parentColumn);
if (String.Compare(value.ToString(), "true", true) == 0)
this.Visible = false;
else
this.Visible = true;
}
base.OnDataBinding(e);
}
#endregion
Listing 11 – this is the code for the Text.ascx.cs file
All you need to do is add the above code Listing 11 the to ReadOnly FieldTemplates that you want to hide in response to the parent in our case its just the Text.ascx.cs file.
#region Event
// added page init to hook-up the event handler
protected void Page_Init(object sender, EventArgs e)
{
if (ParentColumn != null && ParentControl != null)
{
// regiter for the event
ParentControl.StateChanged += StateChanged;
}
}
// consume event
protected void StateChanged(object sender, ChangingAwareEventArgs e)
{
if (ParentColumn != null && ParentControl != null)
{
// show or hide depending on current state of parent
if (String.Compare(e.State, "true", true) == 0)
this.Visible = false;
else
this.Visible = true;
}
}
// added data binding to allow field to be hidden on load
protected override void OnDataBinding(EventArgs e)
{
if (ParentControl != null)
this.Visible = ParentControl.State == "True" ? false : true;
base.OnDataBinding(e);
}
Listing 12 – this is the code for the Text_Edit.ascx and Integer_Edit.ascx files (UPDATED)
Listing 12 code is added to both the Text_Edit.ascx.cs and Integer_Edit.ascx.cs files
Updated: I’ve update the code in the OnDataBinding event handler to fix a bug during insert where there would be no value in the parent filed.
[MetadataType(typeof(ProductMD))]
public partial class Product
{
public class ProductMD
{
public object ProductID {get;set;}
public object ProductName {get;set;}
public object SupplierID {get;set;}
public object CategoryID {get;set;}
[ChangingAware("Discontinued")]
public object QuantityPerUnit {get;set;}
public object UnitPrice {get;set;}
public object UnitsInStock {get;set;}
[ChangingAware("Discontinued")]
public object UnitsOnOrder {get;set;}
[ChangingAware("Discontinued")]
public object ReorderLevel {get;set;}
[ColumnOrder(-1)]
public object Discontinued {get;set;}
// EntitySet
public object Order_Details {get;set;}
// EntityRef
public object Category {get;set;}
public object Supplier {get;set;}
}
}
Listing 13 – the Metadata
As you can see in Listing 13 of the metadata I’ve added the ChangeAware attribute to several columns these will be hidden id the row is discontinued. And to make sure that the children can see the parent when looking for it I’ve added a ColumnOrder attribute to the Discontinued column with a value of –1 for force it to be the first field in the row see Figure 1, 2 and 3 .
Figure 1 – As you can see the bottom row is discontinued and some field are hidden appropriately.
 |
 |
| Figure 2 - normal |
Figure 3 - Discontinued |
So there we have it
Download (UPDATED)
Happy coding 
