I have a VariableSizeWrapGrid and custom drag/drop handling logic. I need to remove (or collapse) the item when it began being dragged. VariableSizeWrapGrid's dataSource is ObservableCollection.
Collapsing (Visibility=Collapsed) an item does not work: it becomes invisible, but occupies its original space anyway. Invalidating VariableSizeWrapGrid does not get rid of these spaces.
Removing an item does not work because dragging process is aborted by some unknown reasons when i'm removing dragged item from its original source. Removing any other items does not abort dragging. I've overridden void OnItemsChanged(object e) with empty handler (not calling base version), but this does not help too.
Short code sample:
void VariableGridView_DragItemsStarting(object sender, DragItemsStartingEventArgs e)
{
var tile = e.Items[0] as Tile;
tile.removeFromOwnerContainer(); // this line interrupts dragging
}
Related
Universal Windows 8.1 Store project here.
I want to know, when a ListView stops scrolling after user interaction. I found plenty of information on the net, but not one example reliably working on WP 8.1 (WPF/WP8 examples do not help much, and there are loads of them).
Here's what I do now.
1. The ListView
<ListView
x:Name="MessageList"
ItemsSource="{Binding Messages}"
VerticalAlignment="Bottom"
ItemContainerStyle="{StaticResource ChatListViewItemStyle}"
PointerEntered="MessageList_OnPointerEntered"
>
<ListView.ItemTemplate>
<DataTemplate>
<messages:MessageContainer />
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
2. The ScrollViewer
I get a ScrollViewer reference from the ListView in code behind.
// GetChildElement<T>(this DependencyObject root) is a simple extension method of mine
Scroll = MessageList.GetChildElement<ScrollViewer>();
3. ListViewer.PointerEntered and ScrollViewer.ViewChanged
PointerEntered handler is used to detect the start of user interaction. When an interaction is detected, I subscribe to Scroll.ViewChanged and use IsIntermediate flag of the event to detect when the list stops scrolling (including inertia).
void MessageList_OnPointerEntered(object sender, PointerRoutedEventArgs e)
{
Debug.WriteLine("START MONITORING INTERACTION");
Scroll.ViewChanged += OnViewChangedByUser;
}
void OnViewChangedByUser(object sender, ScrollViewerViewChangedEventArgs e)
{
Debug.WriteLine("WAITING FOR INTERACTION TO END");
if (!e.IsIntermediate) {
Debug.WriteLine("INTERACTION ENDED");
Scroll.ViewChanged -= OnViewChangedByUser;
}
}
This does work to some extent.
The problem
The problem is, ViewChanged is not fired when the list is scrolled to the end/start and the user pulls it out of bounds and releases it, causing it to return back with inertia. So, the interaction start is detected, but the end is not. ViewChanged is not fired at all -- neither with IsIntermediate=True, nor with False.
What is a better way of doing what I want?
Sadly there's no good way to do this on Windows 8.1 aside from repeated polling and checking the ScrollOffset.
I'd just get an array of 10 doubles, and like 10 times a second I'd shift-in the current scroll offset. Than in that same handler check if the last 5 equals to the end of your list than raise an event.
As Tamás Deme puts it, there's no nice way of doing what is required. However, I've found a workaround that works in my case (nothing nice about it though).
In fact, I'm detecting, whether the list is scrolled to the bottom, when the scrolling stops. It's detecting the end of scrolling is what is causing so much trouble.
There are two parts of the problem: 1 - detecting the end of user interaction, 2 - detecting the end of inertia. Suprisingly, there's no good way of solving either of them. Thankfully, what I actually need is just knowing the value of VerticalOffset when scrolling (user-driven or inertia-animated) ceases. I don't actually have to know whether the user is still holding the list or not.
void MessageList_OnPointerEntered(object sender, PointerRoutedEventArgs e)
{
IsScrolledToLastLine = false; // this is to signal, that the user is
// holding the list, and there must be no
// automatic scrolling, when content is
// added to it.
Debug.WriteLine("[*]START MONITORING INTERACTION");
Scroll.ViewChanged += OnViewChangedByUser;
Scroll.LayoutUpdated += OnScrollLayoutUpdated;
}
void OnScrollLayoutUpdated(object sender, object e)
{
// will trigger multiple times during scrolling
// AND
// will trigger when inertia finally stops
// (regardless of the changes of VerticalOffset)
IsScrolledToLastLine = Scroll.ScrollableHeight == Scroll.VerticalOffset;
Debug.WriteLine("Interaction progress: {0}", IsScrolledToLastLine);
}
void OnViewChangedByUser(object sender, ScrollViewerViewChangedEventArgs e)
{
if (!e.IsIntermediate) {
IsScrolledToLastLine = Scroll.ScrollableHeight == Scroll.VerticalOffset;
Debug.WriteLine("Interaction end: {0}", IsScrolledToLastLine);
Scroll.LayoutUpdated -= OnScrollLayoutUpdated;
Scroll.ViewChanged -= OnViewChangedByUser;
}
}
Scroll.LayoutUpdated
LayoutUpdated is fired multiple times during scrolling. Unlike ViewChanged this event is also fired when inertia stops in the situation shown in the picture of the post. Unfortunatelly, there is no way to determine in LayoutUpdated, whether the list stopped scrolling completely or not.
ViewChanged works fine when you actually change VerticalOffset by scrolling; LayoutUpdated covers the over-scrolling situation.
There is another problem though: OnScrollLayoutUpdated may remain subscribed when scrolling over the edges of the list, as ViewChanged will not trigger. Fortunately, I can just ignore that, this doesn't break anything.
From the docs:
Note When a user flips through FlipView content using touch
interaction, a SelectionChanged event occurs only when touch
manipulations are complete. This means that when a user flips through
content quickly, individual SelectionChanged events are not always
generated for every item because the manipulation is still occurring.
Is there a way to configure the FlipView control to fire SelectionChanged for each flip? This behavior makes implementing paging interesting as the user, if flipping fast enough, can flip to the end of the list before more items can be added.
One solution to the problem is to extend the FlipView and monitor its ScrollViewer. Here is a quick sample of what I'm suggesting. Seems to work on horizontal flip view (haven't handled any other cases, and haven't tested too much).
public class FixedFlipView : FlipView {
public ScrollViewer ScrollViewer {
get;
private set;
}
protected override void OnApplyTemplate() {
base.OnApplyTemplate();
this.ScrollViewer = (ScrollViewer)this.GetTemplateChild("ScrollingHost");
this.ScrollViewer.ViewChanged += ScrollViewer_ViewChanged;
}
void ScrollViewer_ViewChanged(object sender, ScrollViewerViewChangedEventArgs e) {
var index = (int)this.ScrollViewer.HorizontalOffset - 2;
if (this.SelectedIndex != index) {
this.SelectedIndex = index;
}
}
}
Some things to note:
You may want to get the ScrollViewer in a different way that does not depend on its name. Like using the method in my answer here. Although, I'd guess this is fine, too.
It may be a better idea to use a separate event for this. In the code above I set the SelectedIndex property, which raises the SelectionChanged event, but it is also very likely to be doing other stuff as well, so it may be a problem in some cases.
I have a problem with adding Item to FlipView dynamically, I have a very simple FlipView and I put these codes in SelectionChanged event:
private void myFlipView_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
TextBlock tb = new TextBlock();
myFlipView.Items.Add(tb);
}
the strange is when I try to swipe between pages with mouse rapidly it works, but if I swipe with finger it stops working and I have to swipe on the page slowly to make it work.
I wish I could express the problem clearly....
I am not sure if I understood correctly? What exactly do you want to achieve?
In your case you are adding a new FlipViewItem which contains a TextBlock every time you navigate throught the FlipView. So theoretically you will never reach the end of a FlipView.
Working on a Metro style app in C#. I have a custom control which inherits from Grid. MyGrid contains some other custom controls. I'm trying to do hit testing on those controls in the PointerReleased handler:
void MyGrid_PointerReleased(object sender, PointerRoutedEventArgs e)
{
PointerPoint pt = e.GetCurrentPoint(this);
var hits = VisualTreeHelper.FindElementsInHostCoordinates(pt.Position, this);
int breakhere = hits.Count();
}
After this code executes, hitCount is 0. If I move the PointerReleased handler one control higher in the visual tree heirarchy then hitCount is correct the first time and 0 after that. I set up a test project with similar XAML layout to try to reproduce the problem and it works correctly every time. So I'm not sure what bad thing I have done that is preventing VisualTreeHelper from working. I'm not really sure how to proceed debugging this. Any ideas what would cause this function to return no results?
I'm trying to speed up my windows phone 7 page load times. I have a 'static' page that has a dynamically created in a Panorama control - static meaning that the content never changes.
On the first load I look at my config file, create the individual PanoramaItem controls and add them to the main Panorama control. I'm trying to keep a List in a static place so that the initial creation would only happen once and I could just add a fully rendered version to my Panorama control when the page was rendered.
Works fine on first load, but when I try to add the cached PanoramaItems to the Panorama control I get the message "Element is already the child of another element". This makes sense since I already added before. But I can see a way to disconnect the PanoramaItems with the first Panorama control...
I could be going about the control caching thing all wrong as well... Let me know if there's another way to do this.
You can use Panorama.Items.Remove(pivotItem) for this
As an example
With the following page fields
PanoramaItem pi;
bool blahShown = false;
On the press of this button, the control is first instantiated and displayed and on subsequent presses removed and readded without instantiation.
private void button1_Click(object sender, RoutedEventArgs e)
{
if (pi == null) {
pi = new PanoramaItem();
pi.Header = "blah";
}
if (blahShown) {
Pano.Items.Remove(pi);
blahShown = false;
} else {
Pano.Items.Add(pi);
blahShown = true;
}
}