I am hoping someone can help me with this. I have an MVVMLight application in which I have an observable collection of objects, in my view-model, bound to the WPF DataGrid's ItemsSource property. Now I want to change the row background color whenever a specific value called "TaskAssignmentStatus" changes for any item inside the observable collection.
However I am getting a XAML Parse error as follows:
{"Operation is not valid while ItemsSource is in use. Access and modify elements with ItemsControl.ItemsSource instead."}
I have read everything I can find regarding that error but I haven't been able to see how to apply anything I have learned from the answers given thus far to my specific situation. I am very much a new to WPF and databiding so any help would be very much appreciated. Thanks!
The relevant code from my view-model is as follows:
//Contains the actual tasks on the currently selected team member's
//work-list
public ObservableCollection<WorklistTask> TasksForSelectedTeamMember
{
get { return _tasksForSelectedTeamMember; }
set
{
if (value != null)
{
_tasksForSelectedTeamMember = value;
RaisePropertyChanged("TasksForSelectedTeamMember");
}
}
}
Here is the class definition for the types inside my observable collection in the view-model:
public class WorklistTask : ICloneable
{
#region Fields
private int _taskId;
private int _activityId;
private string _activityName;
private string _activityStatus;
private string _taskAssignDate;
private string _activityStartDate;
private string _activityDueDate;
private string _caseStartDate;
private string _caseDueDate;
private int _caseId;
private string _caseType;
//an enum which indicates whether or not the task has been reassigned
private WorkListTaskAssignmentStatus _taskAssignmentStatus;
private int _sourceTaskId;
private bool _selectedByUserInUI = false;
#endregion
#region Constructors
public WorklistTask() { }
#endregion
#region Properties
[DisplayName("Task Assignment Status")]
public WorkListTaskAssignmentStatus TaskAssignmentStatus
{
get { return _taskAssignmentStatus; }
set { _taskAssignmentStatus = value; }
}
public int TaskId
{
get { return _taskId; }
set { _taskId = value; }
}
public int ActivityId
{
get { return _activityId; }
set { _activityId = value; }
}
[DisplayName("Activity Name")]
public string ActivityName
{
get { return _activityName; }
set { _activityName = value; }
}
[DisplayName("Activity Status")]
public string ActivityStatus
{
get { return _activityStatus; }
set { _activityStatus = value; }
}
[DisplayName("Task Assigned Date")]
public string TaskAssignDate
{
get { return _taskAssignDate; }
set { _taskAssignDate = value; }
}
[DisplayName("Activity Start Date")]
public string ActivityStartDate
{
get { return _activityStartDate; }
set { _activityStartDate = value; }
}
[DisplayName("Activity Due Date")]
public string ActivityDueDate
{
get { return _activityDueDate; }
set { _activityDueDate = value; }
}
[DisplayName("Case Start Date")]
public string CaseStartDate
{
get { return _caseStartDate; }
set { _caseStartDate = value; }
}
[DisplayName("Case Due Date")]
public string CaseDueDate
{
get { return _caseDueDate; }
set { _caseDueDate = value; }
}
[DisplayName("Case Id")]
public int CaseId
{
get { return _caseId; }
set { _caseId = value; }
}
[DisplayName("Case Type")]
public string CaseType
{
get { return _caseType; }
set { _caseType = value; }
}
public int SourceTaskId
{
get { return _sourceTaskId; }
set { _sourceTaskId = value; }
}
public bool SelectedByUserInUI
{
get { return _selectedByUserInUI; }
set { _selectedByUserInUI = value; }
}
#endregion
#region Methods
public object Clone()
{
WorklistTask newWorklistTask = (WorklistTask)this.MemberwiseClone();
newWorklistTask.ActivityName = string.Copy(ActivityName);
newWorklistTask.ActivityStatus = string.Copy(ActivityStatus);
newWorklistTask.TaskAssignDate = string.Copy(TaskAssignDate);
newWorklistTask.ActivityStartDate = string.Copy(ActivityStartDate);
newWorklistTask.ActivityDueDate = string.Copy(ActivityDueDate);
newWorklistTask.CaseStartDate = string.Copy(CaseStartDate);
newWorklistTask.CaseDueDate = string.Copy(CaseDueDate);
newWorklistTask.CaseType = string.Copy(CaseType);
return newWorklistTask;
}
#endregion
}
Here is the enum:
public enum WorkListTaskAssignmentStatus
{
Automatic,
Added,
Removed,
DeleteLocal
}
Here is the XAML for the datagrid I am trying to format:
<DataGrid x:Name="WorklistOfSelectedTeamMember"
ItemsSource="{Binding TasksForSelectedTeamMember, Mode=TwoWay,
UpdateSourceTrigger=PropertyChanged}"
AutoGeneratingColumn="GenerateColumnsForWorklist"
IsReadOnly="True"
FontWeight="Normal"
FontSize="13"
SelectionMode="Extended"
AlternatingRowBackground="LightGray"
Grid.Column="0"
Grid.ColumnSpan="2"
Grid.Row="3"
Margin="0,0,5,0"
HorizontalScrollBarVisibility="Auto"
Height="150"
Style="{StaticResource DataGridColoring}">
<i:Interaction.Triggers>
<i:EventTrigger EventName="SelectionChanged">
<cmd:EventToCommand Command="{Binding
WorklistTaskSelectionChangedCommand}"
CommandParameter="{Binding SelectedItems,
ElementName=WorklistOfSelectedTeamMember}" />
</i:EventTrigger>
</i:Interaction.Triggers>
<Style TargetType="DataGridRow">
<Style.Triggers>
<DataTrigger Binding="{Binding TaskAssignmentStatus}"
Value="Automatic">
<Setter Property="Background" Value="Transparent"/>
</DataTrigger>
<DataTrigger Binding="{Binding TaskAssignmentStatus}"
Value="Removed">
<Setter Property="Background" Value="#C4FF0000"/>
</DataTrigger>
<DataTrigger Binding="{Binding TaskAssignmentStatus}"
Value="Added">
<Setter Property="Background" Value="#00FF7F"/>
</DataTrigger>
<DataTrigger Binding="{Binding TaskAssignmentStatus}"
Value="DeleteLocal">
<Setter Property="Background" Value="#00FFFFFF"/>
</DataTrigger>
</Style.Triggers>
</Style>
</DataGrid>
You can get rid of the error you are getting by adding the implicit RowStyle to the Resources dictionary of the DataGrid:
<DataGrid x:Name="WorklistOfSelectedTeamMember"
ItemsSource="{Binding TasksForSelectedTeamMember, Mode=TwoWay,
UpdateSourceTrigger=PropertyChanged}"
IsReadOnly="True"
FontWeight="Normal"
FontSize="13"
SelectionMode="Extended"
AlternatingRowBackground="LightGray"
Grid.Column="0"
Grid.ColumnSpan="2"
Grid.Row="3"
Margin="0,0,5,0"
HorizontalScrollBarVisibility="Auto"
Height="150">
<i:Interaction.Triggers>
<i:EventTrigger EventName="SelectionChanged">
<cmd:EventToCommand Command="{Binding
WorklistTaskSelectionChangedCommand}"
CommandParameter="{Binding SelectedItems,
ElementName=WorklistOfSelectedTeamMember}" />
</i:EventTrigger>
</i:Interaction.Triggers>
<DataGrid.Resources>
<Style TargetType="DataGridRow">
<Style.Triggers>
<DataTrigger Binding="{Binding TaskAssignmentStatus}"
Value="Automatic">
<Setter Property="Background" Value="Transparent"/>
</DataTrigger>
<DataTrigger Binding="{Binding TaskAssignmentStatus}"
Value="Removed">
<Setter Property="Background" Value="#C4FF0000"/>
</DataTrigger>
<DataTrigger Binding="{Binding TaskAssignmentStatus}"
Value="Added">
<Setter Property="Background" Value="#00FF7F"/>
</DataTrigger>
<DataTrigger Binding="{Binding TaskAssignmentStatus}"
Value="DeleteLocal">
<Setter Property="Background" Value="#00FFFFFF"/>
</DataTrigger>
</Style.Triggers>
</Style>
</DataGrid.Resources>
</DataGrid>
Also note that if you want the background colour of the row to change when you set the value of the TaskAssignmentStatus property of an item in your ObservableCollection to a new value dynamically at runtime, the WorklistTask class should implement the INotifyPropertyChanged interface and raise the PropertyChanged event in the setter of the TaskAssignmentStatus property.