RadSplitContainer splitContainer = new RadSplitContainer(); WebBrowser browser = new WebBrowser(); browser.Navigate("http://www.facebook.com"); RadPane browserPane = new RadPane(); browserPane.Header = "Facebook Widget"; browserPane.Content = browser; splitContainer.Items.Add(browserPane); this.HomePageDocking.Items.Add(splitContainer);Rod
Hi,
I have a hierarchy gridview where the rows in each childgrid have a column with a checkbox for its value. When the user clicks on that checkbox, I want that child row to enter the parent grid and that child's parent to enter the child grid. In other words, I want to flip-flop the parent row and selected child row.
My problem is I am having trouble finding an event that captures what child row was selected and if they indeed checked off the check box.
I tried to provide screenshots, but I'm having some trouble pasting them into this message. Not sure if it's possible to do so.
Please let me know if you need any additional information.
Thank you,
Joe
I'm wondering how the filters in RadGridView work. How do they check for equality?
After some experimentation it seems that they check for "referential equality" (is that what is it called??), that is the filter checks if the rows have exactly the same object as the filter. So even if a column shows a custom type of mine and I have implemented the Equals() method, it won't matter.
Lets say I
have a custom type representing a customer:
public class Customer : IComparable{ public int Id { get; set; } public string Name { get; set; } public Customer(int id, string name) { Id = id; Name = name; } public override string ToString() { return Name; } public virtual int CompareTo(object obj) { Customer otherCustomer = obj as Customer; if (otherCustomer != null) { return this.Id.CompareTo(otherCustomer.Id); } else { throw new ArgumentException("Can only compare to other Customer instances."); } } public override bool Equals(object obj) { if (obj.GetType() == typeof(Customer)) { Customer otherCustomer = (Customer) obj; return otherCustomer.Name == Name; } else { return false; } }}I'm using MVVM and each row displayed in the gridview has a viewmodel. This viewmodel has the following code:
private Customer _contact;public Customer Contact{ get { return _contact; } set { if (value != _contact) { _contact = value; OnPropertyChanged("Contact"); } }}public BindingList<Customer> AllContacts { get; private set;}The row-viewmodel has a property called "Contact" that is of my custom type. It also has a BindingList of the same type that will contain all available contact/customers.
And in my XAML I have this code:
<tgv:RadGridView ItemsSource="{Binding Path=MyData, Mode=OneWay}" > <tgv:RadGridView.Columns> <!-- Columns excluded for brevity... --> <tgv:GridViewDataColumn Name="ContactColumn" Header="Contact" DataMemberBinding="{Binding Path=Contact}"> <tgv:GridViewDataColumn.CellTemplate> <DataTemplate> <TextBlock Text="{Binding Path=Contact.Name, Mode=OneWay, UpdateSourceTrigger=PropertyChanged}" /> </DataTemplate> </tgv:GridViewDataColumn.CellTemplate> <tgv:GridViewDataColumn.CellEditTemplate> <DataTemplate> <ti:RadComboBox ItemsSource="{Binding Path=AllContacts, Mode=OneTime}" DisplayMemberPath="Name" SelectedItem="{Binding Path=Contact, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" /> </DataTemplate> </tgv:GridViewDataColumn.CellEditTemplate> </tgv:GridViewDataColumn> </tgv:RadGridView.Columns></tgv:RadGridView>As you can see the column that shows the contact binds to the property Contact on the row-viewmodel. In the cell edit template there's a ComboBox that allows the user to choose one contact from the list with all contacts.
"MyData" that the gridview is bound to is a QueryableCollectionView that has all the rows (row-viewmodels) that are to be displayed. It is created something like this:
RadObservableCollection<DataRowViewModel> myDataRows = new RadObservableCollection<DataRowViewModel>();//...Here would be some code to fill myDataRows with row-viewmodels...MyData = new QueryableCollectionView(myDataRows);
All this works fine.
Now I want to apply filtering on that column by code. Let's say that there are ten available customers. If I open the filter popup on the gridview all ten are displayed in the list of checkboxes where you can specify which ones to show. These are the "distict filters". To apply distinct filters in code behind I would do something like this:
MyData.FilterDescriptors.Clear(); //Clear old filters
ColumnFilterDescriptor cfd = new ColumnFilterDescriptor(ContactColumn);FilterDescriptor fd = new FilterDescriptor();fd.Member = "Contact";fd.Operator = FilterOperator.IsEqualTo;fd.Value = new Customer(1, "David");fd.IsCaseSensitive = true;cfd.DistinctFilter.FilterDescriptors.Add(fd);MyData.FilterDescriptors.Add(cfd);When I run this I see that a filter is applied, but all my rows are removed by the filter, even those that has Id=1 and Name=David.
I have tried a different model where I don't create a new Customer and put in the Value of the filter but instead put an instance of Customer that is actually in the list AllCustomers. When I do this it works fine. The filter removes all rows except those who has that specific customer (David) as customer. This leads me to think that the filter checks equality by checking "referential equality" and does not use the Equals method.
Am I right in this assumption or is it something else I'm missing?
<telerik:RadDocking> <telerik:RadSplitContainer Orientation="Horizontal" InitialPosition="DockedLeft"> <telerik:RadPaneGroup prism:RegionManager.RegionName="Left"/> </telerik:RadSplitContainer> <Grid> <Grid.RowDefinitions> <RowDefinition Height="0.5*"/> <RowDefinition Height="0.5*"/> </Grid.RowDefinitions> <telerik:DocumentHost> <telerik:RadSplitContainer> <telerik:RadPaneGroup prism:RegionManager.RegionName="Main1"/> </telerik:RadSplitContainer> </telerik:DocumentHost> <telerik:DocumentHost Grid.Row="1"> <telerik:RadSplitContainer> <telerik:RadPaneGroup prism:RegionManager.RegionName="Main2"/> </telerik:RadSplitContainer> </telerik:DocumentHost> </Grid></telerik:RadDocking>GridView in WPF Q1 2011 throws a Null Pointer Exception when trying to deselect a previously selected row.
I've tried:
DocumentGrid.UnselectAll()
DocumentGrid.SelectedItems.Clear()
DocumentGrid.SelectedItem = Nothing
All trigger the exception as does Grouping when a row is selected.
The problem only occurs when using an IEnumerable as an ItemsSource. Changing this to mysource.ToList() fixes the problem.
System.Reflection.TargetInvocationException was unhandled Message=Exception has been thrown by the target of an invocation. Source=mscorlib StackTrace: at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks) at System.Delegate.DynamicInvokeImpl(Object[] args) at System.Windows.RoutedEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget) at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target) at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs) at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised) at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args) at System.Windows.UIElement.RaiseEvent(RoutedEventArgs e) at Telerik.Windows.Controls.DataControl.RaiseSelectionChangedEvent(SelectionChangeEventArgs args) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\DataControl.Selection.cs:line 391 at Telerik.Windows.Controls.GridView.GridViewDataControl.RaiseSelectionChangedEvent(SelectionChangeEventArgs args) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Controls\GridView\GridView\GridView\GridViewDataControl.Selection.cs:line 347 at Telerik.Windows.Controls.DataControl.RaiseSelectionChangedEvent(ItemSelectionChange selectionChange) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\DataControl.Selection.cs:line 381 at Telerik.Windows.Controls.DataControl.Telerik.Windows.Data.Selection.ISelectorInternal.RaiseSelectionChangedEvent(ItemSelectionChange selectionChange) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\DataControl.Selection.cs:line 528 at Telerik.Windows.Data.Selection.ItemSelectionHandler.RaiseSelectionChanged(ItemSelectionChange selectionChange) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Selection\ItemSelectionHandler.cs:line 928 at Telerik.Windows.Data.Selection.ItemSelectionHandler.RaiseSelectionChangedAndSyncCurrentWithSelectedIfNeeded(ItemSelectionChange selectionChange) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Selection\ItemSelectionHandler.cs:line 712 at Telerik.Windows.Data.Selection.ItemSelectionHandler.EndAllowedSelection(ItemSelectionChange selectionChange) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Selection\ItemSelectionHandler.cs:line 649 at Telerik.Windows.Data.Selection.ItemSelectionHandler.EndPendingSelection(ItemSelectionChange pendingSelection) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Selection\ItemSelectionHandler.cs:line 619 at Telerik.Windows.Data.Selection.ItemSelectionHandler.EndSelection() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Selection\ItemSelectionHandler.cs:line 600 at Telerik.Windows.Data.Selection.ItemSelectionHandler.DeselectAllNonExistentItems() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Selection\ItemSelectionHandler.cs:line 318 at Telerik.Windows.Data.Selection.ItemSelectionHandler.HandleItemsReset() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Selection\ItemSelectionHandler.cs:line 295 at Telerik.Windows.Data.Selection.ItemSelectionHandler.HandleItemsChanged(NotifyCollectionChangedEventArgs itemsChangedArguments) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Selection\ItemSelectionHandler.cs:line 187 at Telerik.Windows.Controls.GridView.Selection.CompositeSelectionHandler.Items_CollectionChanged(Object sender, NotifyCollectionChangedEventArgs e) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Controls\GridView\GridView\Selection\CompositeSelectionHandler.cs:line 63 at System.Collections.Specialized.NotifyCollectionChangedEventHandler.Invoke(Object sender, NotifyCollectionChangedEventArgs e) at Telerik.Windows.Data.DataItemCollection.OnCollectionChanged(NotifyCollectionChangedEventArgs e) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\DataItemCollection.cs:line 665 at Telerik.Windows.Data.DataItemCollection.OnCollectionViewCollectionChanged(NotifyCollectionChangedEventArgs e) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\DataItemCollection.cs:line 642 at Telerik.Windows.Data.DataItemCollection.Telerik.Windows.Data.IWeakEventListener<System.Collections.Specialized.NotifyCollectionChangedEventArgs>.ReceiveWeakEvent(Object sender, NotifyCollectionChangedEventArgs e) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\DataItemCollection.cs:line 1046 at Telerik.Windows.Data.WeakEvent.WeakListener`1.Handler(Object sender, TArgs args) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\WeakEvents\WeakEvent.cs:line 33 at Telerik.Windows.Data.QueryableCollectionView.OnCollectionChanged(NotifyCollectionChangedEventArgs args) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\QueryableCollectionView.cs:line 679 at Telerik.Windows.Data.QueryableCollectionView.RefreshOverride() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\QueryableCollectionView.cs:line 824 at Telerik.Windows.Data.QueryableCollectionView.RefreshInternal() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\QueryableCollectionView.cs:line 771 at Telerik.Windows.Data.QueryableCollectionView.RefreshOrDefer() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\QueryableCollectionView.cs:line 765 at Telerik.Windows.Data.QueryableCollectionView.ProcessSynchronousCollectionChanged(NotifyCollectionChangedEventArgs args) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\QueryableCollectionView.cs:line 1044 at Telerik.Windows.Data.QueryableCollectionView.ProcessCollectionChanged(NotifyCollectionChangedEventArgs args) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\QueryableCollectionView.cs:line 985 at Telerik.Windows.Data.QueryableCollectionView.OnRefresh() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\QueryableCollectionView.cs:line 294 at Telerik.Windows.Data.QueryableCollectionView.Refresh() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\QueryableCollectionView.cs:line 288 at Telerik.Windows.Data.QueryableCollectionView.EndDefer() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\QueryableCollectionView.Defer.cs:line 60 at Telerik.Windows.Data.QueryableCollectionView.DeferHelper.Dispose() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\QueryableCollectionView.Defer.cs:line 95 at Telerik.Windows.Data.DataItemCollection.EndDefer() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\DataItemCollection.ICollectionView.cs:line 208 at Telerik.Windows.Data.DataItemCollection.DeferHelper.Dispose() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Data\Collections\DataItemCollection.ICollectionView.cs:line 231 at Telerik.Windows.Controls.GridView.GridViewDataControl.PerformGrouping(IGroupDescriptor descriptor, Nullable`1 insertionIndex, GroupingEventAction action) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Controls\GridView\GridView\GridView\GridViewDataControl.Grouping.cs:line 182 at Telerik.Windows.Controls.GridView.GridViewDataControl.<>c__DisplayClass36.<RequestGrouping>b__35() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Controls\GridView\GridView\GridView\GridViewDataControl.Grouping.cs:line 137 at Telerik.Windows.Controls.CursorManager.PerformTimeConsumingOperation(FrameworkElement frameworkElement, Action action) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Controls\CursorManager.cs:line 16 at Telerik.Windows.Controls.GridView.GridViewDataControl.RequestGrouping(IGroupDescriptor descriptor, Nullable`1 insertionIndex, GroupingEventAction action) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Controls\GridView\GridView\GridView\GridViewDataControl.Grouping.cs:line 127 at Telerik.Windows.Controls.GridView.DragDropController.OnGroupPanelDropInfo(Object sender, DragDropEventArgs e) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Controls\GridView\GridView\GridView\DragDrop\DragDropController.GroupPanel.cs:line 97 at Telerik.Windows.Controls.DragDrop.DragDropEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Controls\DragDrop\DragDropEventArgs.cs:line 45 at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target) at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs) at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised) at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args) at System.Windows.UIElement.RaiseEvent(RoutedEventArgs e) at Telerik.Windows.Controls.DragDrop.RadDragAndDropManager.DragDropProvider_DropInfo(Object sender, DragDropEventArgs e) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Controls\DragDrop\RadDragAndDropManager.cs:line 319 at Telerik.Windows.Controls.DragDrop.DragDropProviderBase.RaiseDropInfo() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Controls\DragDrop\DragProviders\DragDropProviderBase.cs:line 170 at Telerik.Windows.Controls.DragDrop.SimulatedDragDropProvider.OnDrop() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Controls\DragDrop\DragProviders\SimulatedDragDropProvider.cs:line 342 at Telerik.Windows.Controls.DragDrop.SimulatedDragDropProvider.OnCoverRectangleMouseLeftButtonUpInternal() in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Controls\DragDrop\DragProviders\SimulatedDragDropProvider.cs:line 241 at Telerik.Windows.Controls.DragDrop.WPFSimulatedDragDropProvider.OnCoverRectangleMouseLeftButtonUp(Object sender, EventArgs e) in c:\Builds\WPF_Scrum\Release_WPF\Sources\Development\Core\Controls\DragDrop\DragProviders\WPFSimulatedDragDropProvider.cs:line 391 at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget) at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target) at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs) at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised) at System.Windows.UIElement.ReRaiseEventAs(DependencyObject sender, RoutedEventArgs args, RoutedEvent newEvent) at System.Windows.UIElement.CrackMouseButtonEventAndReRaiseEvent(DependencyObject sender, MouseButtonEventArgs e) at System.Windows.UIElement.OnMouseUpThunk(Object sender, MouseButtonEventArgs e) at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget) at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target) at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs) at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised) at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args) at System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted) at System.Windows.Input.InputManager.ProcessStagingArea() at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input) at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport) at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel) at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at System.Windows.Interop.HwndSource.InputFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter) at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler) at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler) at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Boolean isSingleParameter) at System.Windows.Threading.Dispatcher.Invoke(DispatcherPriority priority, Delegate method, Object arg) at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam) at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg) at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame) at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame) at System.Windows.Threading.Dispatcher.Run() at System.Windows.Application.RunDispatcher(Object ignore) at System.Windows.Application.RunInternal(Window window) at System.Windows.Application.Run(Window window) at System.Windows.Application.Run() at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args) at System.AppDomain.nExecuteAssembly(Assembly assembly, String[] args) at System.Runtime.Hosting.ManifestRunner.Run(Boolean checkAptModel) at System.Runtime.Hosting.ManifestRunner.ExecuteAsAssembly() at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext, String[] activationCustomData) at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext) at System.Activator.CreateInstance(ActivationContext activationContext) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssemblyDebugInZone() at System.Threading.ThreadHelper.ThreadStart_Context(Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart() InnerException: System.NullReferenceException Message=Object reference not set to an instance of an object.
Hi,
I am trying to style a RadChart. It is a bargraph (set from code) and I want to change the default colors of the bars. So I used the RadChart.PaletteBrushes and defined SolidBrush colors(Found this method in the following link : http://www.telerik.com/help/wpf/radchart-styling-and-appearance-styling-chart-series.html) as follows:
<telerik:RadChart Background="Transparent" HorizontalContentAlignment="Center" HorizontalAlignment="center">
<telerik:RadChart.PaletteBrushes>
<SolidColorBrush Color="#FF0B3F74"/>
<SolidColorBrush Color="#FF721111"/>
<SolidColorBrush Color="#FFA1720B"/>
</telerik:RadChart.PaletteBrushes>
</telerik:RadChart>
But now, an exception as follows occurs while running the application :
'System.Windows.Media.SolidColorBrush' must have IsFrozen set to false to modify.
This exception occurs randomly. Also, in the stack trace, there is a mention of RadTransition Control too. Why could this error be occuring? How can it be solved?