Edit:
Simple answer: Yes, it does. I found the error, which was, that another event handler was added, everytime the Combobox_SelectionChanged was fired. Hence, the collection looked fine, but the Items_CollectionChanged was fired multiple times. Once this was fixed, everything worked fine.
End Edit.
I've got a page with a combobox and a grid. The grid fills dynamically, when the selection in the combobox changes. I'm now observing a strange thing. When I select a value for the second time in the combobox, the childitems in the grid appear twice. I've checked the underlying collections, which look fine (i.e. only one record per item). When I jump out of the combobox_SelectionChanged method, after the Grid.Children.Clear() command, the screen looks fine, i.e. empty.
My guess is, that Grid.Children.Clear() only removes the controls from the visual tree, but the actual controls are still hanging around. Any Ideas?
private void combobox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
grItems.Children.Clear();
grItemsColumnDefinitions.Clear();
grItemsColumnDefinitions.Add(new ColumnDefinition() { Width = new GridLength(200) });
}
private void Items_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
if (e.Action == NotifyCollectionChangedAction.Add)
{
grItems.Children.Add(new ChildItemControl(e.NewItems[0]));
}
}
Edit: The whole thing is supposed to look like this (fictional - but hopefully understandable - example)
I would suggest you use the built in Databinding for WPF. You could use something like this:
<DataGrid x:Name="grItems" ItemsSource="{Binding comboboxItems}" />
Then, when you update comboboxItems your grid will automatically update too!
Here is a great article on Databinding with the DataGrid control:
http://www.wpftutorial.net/DataGrid.html
For more information about Databinding in general, here is a good article: https://msdn.microsoft.com/en-us/library/aa480224.aspx
Related
I'm a fairly new to WPF and C#.
I have a frame component on my main window and 4 buttons next to it that navigate to different views in the frame. Within one the the views there is a DataGrid that has a SelectionChanged event which makes an SQL call to a database that fetches records, whose data is then used to populate a list of custom objects (these relate to the selected item on the DataGrid).
Anyways, the problem I have is that from time to time multiple calls (2 or 3) to the SelectionChanged event are being triggered at the same time for a single selection change (mouseclick) on the DataGrid.
The navigation button click events on the main window all look like this:
private void btn_MyDesk_Click(object sender, RoutedEventArgs e)
{
MainFrame.Navigate(new Uri("/Views/MyDeskView.xaml", UriKind.Relative));
}
private void btn_AllOrders_Click(object sender, RoutedEventArgs e)
{
MainFrame.Navigate(new Uri("/Views/AllOrdersView.xaml", UriKind.Relative));
}
After some experiementation, I've found that the bug only happens after changing views away from the view with the DataGrid, and then changing back to it (but not always). When the bug appears the number of calls generally corresponds to the number of times I had switched views. Furthermore, the bug will simply vanish if leave the program alone for a minute or two. This makes me suspect that there multiple instances of the DataGrid view lingering like ghosts in memory and duplicating event calls until they are cleaned up by a garbage collector.
Should I be cleaning something up each time I switch views, or am I looking in the wrong place?
Thank you in advance for any help.
Edit: In answer to #Peter Moore
I subscribe to the event in the DataGrid declaration within the views XAML: SelectionChanged="dtg_MyDeskOrderGrid_SelectionChanged"
Edit: This is the sequence that happens on a selection change in the data grid. It includes several UI changes while the SQL records for the new selection are retrieved and displayed on a second DataGrid (dtg_MyDeskOrderItems). While the SQL call is being made, the relevant controls are disbaled and a semi-transparent panel (bdr_DGLoadingPanel) is moved on screen to cover them and display a loading animation. When the work is done, the work area is re-enabled and the loading panel moved off screen. Focus is also returned to the main "order" Datagrid.
dtg_MyDeskOrderGrid: This is the main DataGrid showing all "Orders"
dtg_MyDeskOrderItems: This is a secondary DataGrid that is updated to show all "Items" in the selected order.
private void dtg_MyDeskOrderGrid_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
CurrSelectedOrder = (Order_class)dtg_MyDeskOrderGrid.SelectedItem;
if (CurrSelectedOrder.ItemList == null)
{
if (NowWorking == false)
{
NowWorking = true;
bdr_DGLoadingPanel.Margin = new Thickness(2);
dtg_MyDeskOrderGrid.IsEnabled = false;
bdr_FilterPanel.IsEnabled = false;
bdr_DGLoadingPanel.Focus();
img_LoadingCircle.RenderTransform = rt;
img_LoadingCircle.RenderTransformOrigin = new Point(0.5, 0.5);
da.RepeatBehavior = RepeatBehavior.Forever;
rt.BeginAnimation(RotateTransform.AngleProperty, da);
bdr_DGLoadingPanel.UpdateLayout();
worker.RunWorkerAsync();
}
}
else
{
dtg_MyDeskOrderItems.ItemsSource = null;
dtg_MyDeskOrderItems.ItemsSource = CurrSelectedOrder.ItemList;
dtg_MyDeskOrderItems.Items.Refresh();
}
}
private void worker_DoWork(object? sender, DoWorkEventArgs e)
{
DatabaseConnection DBConn9 = new DatabaseConnection();
DBConn9.FillOrderItems(CurrSelectedOrder);
}
private void worker_RunWorkerCompleted(object? sender, RunWorkerCompletedEventArgs e)
{
this.Dispatcher.Invoke(() =>
{
dtg_MyDeskOrderItems.ItemsSource = null;
dtg_MyDeskOrderItems.ItemsSource = CurrSelectedOrder.ItemList;
dtg_MyDeskOrderItems.Items.Refresh();
bdr_DGLoadingPanel.Margin = new Thickness(1000, 2, 2, 2);
rt.BeginAnimation(RotateTransform.AngleProperty, null);
dtg_MyDeskOrderGrid.IsEnabled = true;
bdr_FilterPanel.IsEnabled = true;
// The following work-around and accompanying GetDataGridCell function were used to give keyboard focus back to the datagrid to make navigation with arrow keys work again.
// It appears keyboard focus is not returned to the Datagrid cells when using the Datagrid.focus() method.
Keyboard.Focus(GetDataGridCell(dtg_MyDeskOrderGrid.SelectedCells[0]));
NowWorking = false;
});
}
Edit...
Following the advice of the commentors, I was able to fix the bug by unsubscribing from the event in the Unloaded event for the view containing the DataGrid:
private void uct_MyDeskView_Unloaded(object sender, RoutedEventArgs e)
{
dtg_MyDeskOrderGrid.SelectionChanged -= dtg_MyDeskOrderGrid_SelectionChanged;
}
However, I was not able to reproduce the bug using a barebones testing project.
The UI in the original project is quite heavy, so I'm wondering if it's not the old view and events lingering in memory as this seems to fit the behavior of the bug & fix (Only occuring when I navigate away and back causing a new view to be created, multiple event triggers corresponding to the number of times I navigated away, and then finally the bug vanishing of its own accord after a moment or two).
I won't be settling on this as a final solution and instead will learn about ways I can reuse instances of my views (as suggested by Bionic) instead of recreating them. The reason for this is, if the SelectionChanged event is getting multiple triggers from old view instances, then it is likely other events will suffer from the same bug. This would be bad.
#BionicCode If you are still around, could you repost your initial comment as a solution so I can mark it answered?
Thank you to everyone for all the help and education. ^_^
Following the advice of the commentors, I was able to initially fix the bug by unsubscribing from the event in the Unloaded event for the view containing the DataGrid:
private void uct_MyDeskView_Unloaded(object sender, RoutedEventArgs e)
{
dtg_MyDeskOrderGrid.SelectionChanged -= dtg_MyDeskOrderGrid_SelectionChanged;
}
However as this solution only disconnected the one event and didn't solve the root problem of old views lingering in the background and firing events before being cleaned up, I finally went the following code that keeps only one instance of my view in memory and reuses it.
private MyDeskView? currMyDeskView = null;
private void btn_MyDesk_Click(object sender, RoutedEventArgs e)
{
if (currMyDeskView == null)
{
currMyDeskView = new MyDeskView();
}
MainFrame.Navigate(currMyDeskView);
}
Thank you to everyone who helped me get over this bug.
In my application, I need to select the newly created document(note) when I go back to library. After library item is selected, the Library must be scrolled to the selected item.
My library's OnLoaded method:
private async void OnLoaded(object sender, RoutedEventArgs e)
{
await this.ViewModel.InitializeAsync();
// CollectionViewSource of my GridView being filled
ViewModel.CollectionChanging = true;
GroupInfoCVS.Source = ViewModel.GroupsCollection;
ViewModel.CollectionChanging = false;
// Loading Last selected item - THIS CHANGES SELECTION
ViewModel.LoadLastSelection();
}
After I call the LoadLastSelection method, selection is changed successfuly (I've tested). This is the method that is called after that (in our GridView's extended control):
private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
this.SelectedItemsCount = this.SelectedItems.Count;
var newlySelectedItems = e.AddedItems;
if (newlySelectedItems.Any())
{
var item = newlySelectedItems.Last();
ScrollTo(item);
}
}
private void ScrollTo(object item)
{
UpdateLayout();
var itemUI = (FrameworkElement)this.ContainerFromItem(item);
if (itemUI != null)
{
_scrollViewer.UpdateLayout();
_scrollViewer.ChangeView(null, itemUI.ActualOffset.Y - itemUI.ActualHeight, null, false);
}
}
This also works for the most part. When itemUI is not null, the method scrolls successfully to the required item. The problems start when the items start to overflow the screen size. When items are completely hidden from the screen, they are virtualized. That means that ContainerFromItem returns null, so I can't take the offset properties. Keep in mind that this actually occurs before Library's OnLoaded method is finished.
Please, help me with some alternative to get such properties or other methods of scrolling, which will help me scroll successfully.
I've read a lot and tried using Dispatcher.RunAsync and ScrollIntoView methods, but I couldn't manage to produce any scrolling behavior. If you point me how to use them successfully, that would be a nice help too.
Here's what I've read (and tried):
ItemContainerGenerator.ContainerFromItem() returns null?
How to Know When a FrameworkElement Has Been Totally Rendered?
Is there a "All Children loaded" event in WPF
Let ListView scroll to selected item
Thanks in advance!
IMPORTANT: If you don't want to read all the conversation within the official answer, please read the solution in short here:
TemplatedControl's style had changed ScrollViewer's name from "ScrollViewer" to "LibraryScrollViewer" and that rendered ScrollIntoView method useless.
For GridView, the best way to achieve your needs is to call GridView.ScrollIntoView.
But you seem to have made similar attempts, and it does not to be successful, then the following points may help you:
1. Don't use GridView as a child element of ScrollViewer.
In your code, I see that you are calling the method of ScrollViewer.ChangeView to adjust the view scrolling, so it is speculated that you may put the GridView in the ScrollViewer, which is not recommended.
Because there is a ScrollViewer inside the GridView, and its ScrollIntoView method is to change the scroll area of the internal ScrollViewer. When there is a ScrollViewer outside, the ScrollViewer inside the GridView will lose the scrolling ability, thus making the ScrollIntoView method invalid.
2. Implement the Equals method of the data class.
If your data class is not a simple type (such as String, Int32, etc.), then implementing the Equals method of the data class will help the GridView to find the corresponding item.
Thanks.
I'm working with Xamarin.Forms and I made a CustomRenderer for Checkbox in UWP. When I set all the Checkboxes of my items in the ListView to true by clicking the button "Alle", the Checkboxes are displayed correctly with the check inside the box:
However, if I hover my mouse over the Checkboxes, they immediately change their appearence (the check disappears but it's still selected). In the following screenshot, I moved my cursor over the 3rd - 7th Checkboxes:
This is my overridden OnElementChanged method in the CustomRenderer:
protected override void OnElementChanged(ElementChangedEventArgs<EvaCheckbox> e)
{
base.OnElementChanged(e);
var model = e.NewElement;
if (model == null)
{
return;
}
nativeCheckbox = new CheckBox();
CheckboxPropertyChanged(model, null);
model.PropertyChanged += OnElementPropertyChanged;
nativeCheckbox.Checked += (object sender, Windows.UI.Xaml.RoutedEventArgs eargs) =>
{
model.IsChecked = (bool)nativeCheckbox.IsChecked;
};
nativeCheckbox.Unchecked += (object sender, Windows.UI.Xaml.RoutedEventArgs eargs) =>
{
model.IsChecked = (bool)nativeCheckbox.IsChecked;
};
SetNativeControl(nativeCheckbox);
}
I tried to override the PointerEntered event of nativeCheckbox. It works, for example if I set the model.IsChecked to true on this event, it will be set to true:
nativeCheckbox.PointerEntered += (s, args) =>
{
model.IsChecked = true;
};
But I don't know how to (if even at this place) prevent the checkbox from changing it's appearance when moving the cursor above the Checkbox. Just leaving the triggered event with empty code like this won't change anything about the described behaviour:
nativeCheckbox.PointerEntered += (s, args) => { };
How can I prevent the Checkbox from changing it's appearance when I move my cursor over it?
Update:
I've created a sample project for this issue. You can find the repository here: https://github.com/Zure1/CustomCheckbox
It has the exact same described behavior. In the following screenshot I pressed the button "All" on the bottom of the screen and then the checkboxes look like correct with a check inside of them:
After moving the mouse cursor over the bottom 3 checkboxes, their change their appearance:
Information: I'm debugging on my desktop (Windows 10). I don't know if this issue exists on WinPhone. Just in case you're wondering why my checkboxes are red: My system color in Windows is red.
This is a tricky one as I have been struggling with this issue for a while, I'll try my best to answer this.
TL;DR: It's caused by ViewCell.
The issue comes down to Xamarin Forms ListView and ViewCell.
I haven't been able to track down the cause yet for many months and the way I get around this issue is by refreshing the ListView every time a change happens forcing a redraw of the entire ListView which can really impact performance.
My educated guess on what the cause could be is the rendering code for the ViewCell is missing something.
As for your particular issue, I have created a CheckBoxCell which you can use to display a list of checkboxes with a title. I forked your project and made the changes.
This will display something similar to what you are trying to achieve and doesn't have rendering issues so will be a good starting point. You are able to customize this to display images and the like but you'll have to do that in the platform-specific layout code.
Please note that I have only created the code for UWP and that should be enough to get you going for the other platforms.
I hope this helps somewhat.
I am using LongListSelector control on Windows Phone 8 and can't figure out the best way to handle a tap on an item.
The few examples I've found rely on the SelectionChanged event. However, this solution is buggy because if I tap an item that opens a new page, hit back, and then tap the same item again, it won't work because this item is already selected, so SelectionChanged is not triggered.
I tried to register to the tap event and use the current selected item as the tapped one, but some times the current selected item is not the one I expect.
I could wrap my ItemTemplate in a button and handle the tap for each item but I need to reskin the button to make it look like a simple list item.
Finally, I don't understand why it is so complicated to achieve such a basic thing. Is there a simple and standard way I missed?
My second wish is to get an effect on the item when it is tapped. Is there any standard way to do it?
You could null your LongListSelector's SelectedItem at the end of each SelectionChanged event. I.e.
<phone:LongListSelector x:Name="LLS" SelectionChanged="LLS_SelectionChanged">
And the event handler:
private void LLS_SelectionChanged(object sender, SelectionChangedEventArgs e) {
// If selected item is null, do nothing
if (LLS.SelectedItem == null)
return;
// Navigate to the next page
NavigationService.Navigate(new Uri("/nextpage.xaml", UriKind.Relative));
// Reset selected item to null
LLS.SelectedItem = null;
}
You'll fire the SelectionChanged event twice, but nothing's going to happen the second time round and you should get the behaviour that you're looking for - (i.e Setting SelectedItem to null will trigger a new SelectionChanged event, but this second event gets caught in the if-statement)
As for the second part of your question, you might be better posting a new question.
I done it with the Tap event handling.
I prefer not to use Selected property, but get tapped item this way (and I haven't noticed any bugs):
MyListItemClass item = ((FrameworkElement)e.OriginalSource).DataContext
as MyListItemClass;
Also, you could get the original item ContentPresenter simple by navigating up through VisualTree from e.OriginalSource. That way:
ContentPresenter itemPresenter = SomeHelperClass
.FindParent<ContentPresenter>(e.OriginalSource,"");
Where FindParent is similar to find child in this question: How can I find WPF controls by name or type?
ContentPresenter is that object what you need to manually change the item template if you want to (to set "selected" state for example).
private void Item_tap(object sender, RoutedEventArgs e)
{
var element = (FrameworkElement)sender;
DataSource data = (DataSource)element.DataContext;
}
My second wish is to get an effect on the item when it is tapped. Is
there any standard way to do it?
For this the only thing you need to do add this to your control (or stackpanel where you want to have this effect):
<StackPanel toolkit:TiltEffect.IsTiltEnabled="True">
first add this to *.xaml page inside the
LongListSelectorSelectionChanged="listBox_SelectionChanged"
so that it looks like this :
<toolkit:LongListSelector x:Name="listBox" SelectionChanged="listBox_SelectionChanged">
then in the *.xaml.cs file in the event handler
private void listBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
// Write your logic on what you want to do with the selected item
}
In addition to halil´s answer:
First of all you need to install the Windows Phone Toolkit (WPtoolkit) by NuGet.
Than add the namespace declaration on the PhoneApplicationPage.
xmlns:toolkit="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone.Controls.Toolkit"
After this you can add toolkit:TiltEffect.IsTiltEnabled="True" to the control definition.
It is nice documneted by NOKIA:
http://developer.nokia.com/community/wiki/Tilt_Effect_for_Windows_Phone
Oliver
I created a simple AutoCompleteBox in my WPF app and it loads great with code intercepting the Populate event, but when the list pops up and I hit the arrow down key and get to the end of the list the vertical scroll bar doesn't scroll.
The values keep changing in the field like it is scrolling through them, but the scroll bar doesn't move.
If I use the mouse it scrolls fine.
I just need the arrow key to scroll it.
Any ideas/suggestions?
I am new to WPF and have searched forever for this fix.
Attach a SelectionChanged event and then, inside the handler:
private void AutoCompleteBox_OnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
AutoCompleteBox box = (AutoCompleteBox)sender;
ListBox innerListBox = (ListBox) box.Template.FindName("Selector", box);
innerListBox.ScrollIntoView(innerListBox.SelectedItem);
}
I see the same behavior. I found a post on codeplex talking about a different issue but at the bottom of the post they have a class AutoCompleteBoxEx that supports ScrollIntoView, so you can hook up the SelectionChanged even and this should get you the behavior you want. I have no idea why this is not baked in. I have had a chance to test out the posted code.
Update
Just pasted the code from the post into a class and used it in the XAML by changing AutoCompleteBox to AutoCompleteBoxEx and adding namespace for AutoCompleteBoxEx and it worked fine. You don't have to specify any event in the XAML, nor do you need to add any code to the code behind.