I've been developing a WPF application, and I've stumbled upon something interesting, probably because I don't know how it really works underneath.
Basically I'm creating a context menu. The menu has one parent MenuItem, which has three children of the same type. Here's the bare bones code.
public MainWindow()
{
InitializeComponent();
ContextMenu ctxMain = new ContextMenu();
MenuItem parent = CreateMenuItem("Parent", null);
for(int i = 0; i < 3; i++)
{
parent.Items.Add(CreateMenuItem(i.ToString(), () => MessageBox.Show(i.ToString())));
}
ctxMain.Items.Add(parent);
this.ContextMenu = ctxMain;
}
public MenuItem CreateMenuItem(string header, Action action)
{
MenuItem item = new MenuItem();
if (action != null)
{
item.Click += (object sender, RoutedEventArgs e) => action();
}
item.Header = header;
return item;
}
Visually, it's working as expected.
But the action I've given as parameter is acting strange. I'd expect each child item's click to show what's written in their header in the MessageBox. But all of them are displaying '3'.
Am I understanding it correctly, that the inline action I've defined in the for loop, does not get instantiated three times, but only once, using the same parameter 'i'? Or are they three different Action instances, all referring to the same integer? I'd like to hear some clarification to what's going on here.
Thanks in advance.
Regards.
for(int i = 0; i < 3; i++)
{
var localCopy = i;
parent.Items.Add(CreateMenuItem(localCopy.ToString(), () => MessageBox.Show(localCopy.ToString())));
}
Your variable i was "captured" by the lambda expression. But i has changed before your action was executed. And your action executes on the current i, which means 3 (the value i has after the loop and when your action finally executes).
You need to make a local copy of your variable and use that instead. As it has it's own scope inside the loop, it will never change.
Related
I am trying to pass the index of the clicked button in Repeat(int value) and wrote this -
gp.GetComponentInChildren ().onClick.AddListener(() =>
Repeat(rep));
But when I click any button I got the last index of the button for all.
I want to know is there any way, I can pass the index of that button which i clicked in Repeat()?
void chatDialogs() {
foreach (Transform child in this.transform) {
GameObject.Destroy (child.gameObject);
}
for (int i = 5; i > 0 ; i--) {
int currentStep = Laststep - i;
if (currentStep >= 0) {
gp = (GameObject)Instantiate (playerPreFab);
gp.transform.SetParent (this.transform);
}
gp.GetComponentInChildren<Button> ().onClick.AddListener(() =>
Repeat(**transform.GetSiblingIndex()**));
}
public void Repeat(int speakstep) {
Application.ExternalCall("textspeak", speakstep);
}
in speakstep object of Repeat() the clicked button index should be passed, but its getting the last index in every button I click.
I think you can do something like this:
AddButtonListener(gp.GetComponentInChildren<Button> (), i);
inside your for loop,
when AddButtonListener is defined as:
void AddButtonListener(Button b, int index)
{
b.onClick.AddListener(()=>{Repeat(index)});
}
This way you capture the button index in the listener function (but I'm not sure what the correct name of this pattern is), and I wrote this without actually running it. Hope you have enough info now to get it working.
I have problem with my GUI and Threads.
The GUI contains DataGrid. Every X time the program do some query and getting a list of items that I want to fill into the DataGrid.
So far so good:
private void loadTaskList() //Call every X time
{
List<myObject> myList = myquery();
this.Dispatcher.Invoke((Action)(() =>
{
TaskListTable.Items.Clear(); //Clear the DataGrid
foreach (myObject O in myList) //Add the items from the new query.
{
TaskListTable.Items.Add(O);
}
}));
FindSelectionObject(); // <-- see next explanation.
}
When the user click on one of the objects in the datagrid, the line color changed (it works fine), but when the program reload the table,The painted line disappears (Becuse I clear and add new objects).
To deal with it, I created the function FindSelectionObject():
private void FindSelectionObject()
{
this.Dispatcher.Invoke((Action)(() =>
{
this.SelectedIndex = TaskListTable.Items.IndexOf((myObject)lastSelectionObject); //find index of the new object that equels to the last selection object.
var row = TaskListTable.ItemContainerGenerator.ContainerFromIndex(SelectedIndex) as DataGridRow; //get the row with the index
row.Background = Brushes.LightGoldenrodYellow; //repaint
}));
}
The problem: Everything works fine, but sometimes when the program reloads, the line flashes per second and then highlighted back, and sometimes it's not painting it at all (untill the next reload).
I can't understand why this is happening. I think maybe the FindSelectionObject() begins to run before the loadTaskList() ends to invoke all and add the new objects into the datagrid.
But if so - Why? And how can I fix it?
In the bottom line, I want that after every reload the line re-paint immediately..
Thanks for any advice!
A few things to think about:
You should keep in mind that the DataGrid uses virtualization, which means that each item in your items source does not get its very own UI element. The UI elements are created to fill the visible area, and then re-used depending on which data-source item is currently bound to each one (this changes when you scroll for instance or change the items source). This may cause you problems in the future if you use your current approach, so keep this in mind.
The other thing is that the DataGrid may require more "cycles" of the layout process in order to update its UI. You may simply be calling FindSelectionObject prematurely. You have queued FindSelectionObject right after the invocation in loadTaskList. If the DataGrid needs to perform some actions which are queued on the dispatcher after the items source has changed, these will execute after the invocation in FindSelectionObject.
Try this instead:
private void loadTaskList() //Call every X time
{
List<myObject> myList = myquery();
this.Dispatcher.Invoke((Action)(() =>
{
TaskListTable.Items.Clear(); //Clear the DataGrid
foreach (myObject O in myList) //Add the items from the new query.
{
TaskListTable.Items.Add(O);
}
// The items of the grid have changed, NOW we QUEUE the FindSelectionObject
// operation on the dispatcher.
FindSelectionObject(); // <-- (( MOVE IT HERE )) !!
}));
}
EDIT: OK, so if this fails then maybe this will cover the case in which the above solution fails: subscribe to the LoadingRow event of DataGrid and set the appropriate background color if the row is the selected one. So in the cases when new rows are created this event will be called (due to virtualization it is not called per item in items source, but per actual row UI element). In the event args you will have access to the created DataGridRow instance.
I think this issue could be a visual thread synchronization. For this you can create and use a method similar like this:
public void LockAndDoInBackground(Action action, string text, Action beforeVisualAction = null, Action afterVisualAction = null)
{
var currentSyncContext = SynchronizationContext.Current;
var backgroundWorker = new BackgroundWorker();
backgroundWorker.DoWork += (_, __) =>
{
Thread.CurrentThread.CurrentCulture = new System.Globalization.CultureInfo("en-US");
Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo("en-US");
currentSyncContext.Send((t) =>
{
IsBusy = true;
BusyText = string.IsNullOrEmpty(text) ? "Espere por favor..." : text;
if (beforeVisualAction != null)
beforeVisualAction();
}, null);
action();
currentSyncContext.Send((t) =>
{
IsBusy = false;
BusyText = "";
if (afterVisualAction != null)
afterVisualAction();
}, null);
};
backgroundWorker.RunWorkerAsync();
}
IsBusy and BusyText are particular properties, that you can remove. The action variable will be the action to do in background (load your items for instance). beforeVisualAction and afterVisualAction are the visual actions you may want to do before and after the background action. Here are any visual update, for instance select your item, change color, set a view model variable that raise a binding update,... (any action that update the view).
Hope this method helps.
Are you maintaining the reference to lastSelectionObject somewhere? You say you're adding new objects, if they are truly new then the reference will be different and the reference comparison happening in IndexOf will not find it.
I have a ListBox in a Windows Phone app. In a button action I need to set a transformation and name on every ListBoxItem in the ListBox called lb.
My datasource is
var items = new ObservableCollection<string>();
for (int i = 0; i < 10; ++i)
{
items.Add("Item " + i);
}
lb.ItemsSource = items;
I have a code to add a RenderTransform to each ListBoxItem in the ListBox
for (int i = 0; i < items.Count;++i )
{
var item = this.lb.ItemContainerGenerator.ContainerFromIndex(i) as ListBoxItem;
item.RenderTransform = new CompositeTransform();
item.Name = i.ToString() //needed for storybord
//another stuff
}
and it works ok. The problem is that I first need to insert and item to the list. When I call items.Insert(index,"test") before the for loop I get an exception that the item is null when i==index. It does not matter when I insert the new item, I always get null for that item.
What am I doing wrong? Or is there an event of the ListBox I need to wait for when I insert the new item before trying to acces the ListBoxItem?
Edit: I extracted the code and put it into a solution: https://dl.dropboxusercontent.com/u/73642/PhoneApp2.zip. I first insert a fake item to the new solution, the fade it away and move the original item to that position using an animation.
Right after item added there is not container generated because of asynchronous nature of UI subsystem. Try subscribing on the ItemsChanged (or StatusChanged, sorry i don't remember) and get item when event is fired with proper event args.
Waiting for the Dispatcher to finish doing what its doing such as (updating the UI because of a new item being added)
this.Dispatcher.BeginInvoke(() =>
{
//Code Here
});
If you ever manipulate the UI such as adding an item to a listbox without the UI getting updated, you will not be able to run code targeting the UI.
Edit: Here is the code for your project to get working
private void Button_Click(object sender, RoutedEventArgs e)
{
start = Int32.Parse(from.Text);
end = Int32.Parse(to.Text);
fake = items[start];
//items.Insert(end, fake);
this.Dispatcher.BeginInvoke(() =>
{
for (int i = 0; i < items.Count; ++i)
{
var item = this.lb.ItemContainerGenerator.ContainerFromIndex(i) as ListBoxItem;
item.Name = i.ToString();
}
(this.lb.ItemContainerGenerator.ContainerFromIndex(end) as ListBoxItem).RenderTransform = new CompositeTransform();
(this.lb.ItemContainerGenerator.ContainerFromIndex(end) as ListBoxItem).Name = "listBoxItem1";
(this.lb.ItemContainerGenerator.ContainerFromIndex(start) as ListBoxItem).Name = "listBoxItem";
sbListBox.Begin();
});
}
I am trying to get the text value of a "cell" inside of a GridView that is set as the view of a ListView. I do not want to get the SelectedItem of the ListView as that just returns my entire View Model (but not which property the cell refers to).
I am able to get the text value by responding to direct mouse events (up down or whatever) and if the value is a textblock, obviously I can use the text. This works great and as of right now this is my only solution, although its currently limited.
I would like to take it a step further and be able to click anywhere with in the cell area, navigate around to find the appropriate textblock and then use that value. I have tried a half million ways to do this but what seems logical doesn't seem to quite work out like it should.
Setup:
I have a dynamic GridView that creates its own columns and bindings based on data models that I pass to it. I am using a programmatic cell template (shown below) to have individual control over the cells, particularly so I can add a "border" to it making it actually separate out each cell. I have named the objects so I can access them easier when I'm navigating around the VisualTree.
Here is the Template Code. (Note that the content presenter originally was a textblock itself, but this was changed for later flexibility)
private DataTemplate GetCellTemplate(string bindingName)
{
StringBuilder builder = new StringBuilder();
builder.Append("<DataTemplate ");
builder.Append("xmlns='http://schemas.microsoft.com/winfx/");
builder.Append("2006/xaml/presentation' ");
builder.Append("xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml' ");
builder.Append("xmlns:local = 'clr-namespace:XXXXXXXX");
builder.Append(";assembly=XXXXXXXXX'>");
builder.Append("<Border Name=\"border\" BorderThickness=\"1,0,0,0\" BorderBrush=\"Gray\" Margin=\"-6,-3,-6,-3\">");
builder.Append("<Grid Margin=\"6,3,6,3\">");
builder.Append("<ContentPresenter Name=\"content\" HorizontalAlignment=\"Stretch\" Content=\"{Binding ");
builder.Append(string.Format("{0}", bindingName));
builder.Append("}\"/>");
builder.Append("</Grid>");
builder.Append("</Border>");
builder.Append("</DataTemplate>");
DataTemplate cellTemplate= (DataTemplate)XamlReader.Parse(builder.ToString());
return cellTemplate;
}
What I have Tried:
The logical approach for me was to react to a Mouse event. From the object that had the mouse event I would do either
A. Look at its children to find a textblock, or
B. Get its parent then look for child with a textblock.
My assumption is that if I click in white space I'm clicking in a container that has my textblock. So far the two things that come up are a Border and a Rectangle (if I don't click the text itself). A. Returns absolutely nothing except for the recangle and the border. When I do B i can find textblocks but they are every single text block in the entire row.
So what I try to do from that is get all textblocks, then go backwards till I find which one has a IsMouseOver property as true. It turns out none of these objects EVER have a IsMouseOver except the content presenter for the entire row. So this seems to indicate to me is that the whitespace in the cells does not actually contain the textblock.
What I find is that when I click on the Border and start looking at children, I eventually get to a container that has a rectangle (the rectangle I click) and a grid row view presenter. The presenter shows all of the objects inside the row (hence why i would get all textblocks when i do this recursive scan).
Here is some of the code used to do this to get an idea of what i'm doing. I have written about 10 different versions of this same recursive code generally attempting to find who has the Mouse over it and is related to a textbox.
private void OnPreviewMouseUp(object sender, MouseButtonEventArgs e)
{
object original = e.OriginalSource;
if (original is TextBlock)
{
this.valueTextBlock.Text = ((TextBlock)original).Text;
}
else if (original is FrameworkElement)
{
var result = GetAllNestedChildren<Border>(VisualTreeHelper.GetParent((DependencyObject)original)).Where(x => x.Name == "border").Where(x => HasAChildWithMouse(x)).ToList();
}
else
{
this.valueTextBlock.Text = string.Empty;
}
}
private bool HasAChildWithMouse(UIElement element)
{
if (element.IsMouseOver || element.IsMouseDirectlyOver)
return true;
var childCount = VisualTreeHelper.GetChildrenCount(element);
for (int i = 0; i < childCount; ++i)
{
var child = VisualTreeHelper.GetChild(element, i);
if (child is UIElement)
if (HasAChildWithMouse((UIElement)child))
return true;
}
return false;
}
private IEnumerable<T> GetAllNestedChildren<T>(DependencyObject obj) where T : UIElement
{
if (obj is T)
yield return obj as T;
var childCount = VisualTreeHelper.GetChildrenCount(obj);
for (int i = 0; i < childCount; ++i)
{
var child = VisualTreeHelper.GetChild(obj, i);
foreach (var nested in GetAllNestedChildren<T>(child))
yield return nested;
}
}
private T GetObjectByTypeParentHasMouse<T>(DependencyObject obj) where T : UIElement
{
if (obj is T)
{
if ((VisualTreeHelper.GetParent(obj) as UIElement).IsMouseOver )
{
return obj as T;
}
}
var childCount = VisualTreeHelper.GetChildrenCount(obj);
for (int i = 0; i < childCount; ++i)
{
var child = VisualTreeHelper.GetChild(obj, i);
var correctType = GetObjectByTypeParentHasMouse<T>(child);
if (correctType != null)
return correctType;
}
return null;
}
private T GetContainedType<T>(DependencyObject obj, bool checkForMouseOver) where T : UIElement
{
if (obj is T && ((T)obj).IsMouseOver)
return obj as T;
var childCount = VisualTreeHelper.GetChildrenCount(obj);
for (int i = 0; i < childCount; ++i)
{
var child = VisualTreeHelper.GetChild(obj, i);
var correctType = GetContainedType<T>(child, checkForMouseOver);
if (correctType != null)
return correctType;
}
return null;
}
The other approach I took was to start with the TextBlock itself, find its containing parent and find out how i can navigate to the answer. I find the templateparent is the ContentPresenter (named ="content") I find the grid, and then the border. The parent of the border is a content presenter whos content is the data view model for the entire row. The parent of this contentpresenter is the grid column's presenter. This is the same one that i was navigating up to in the other one.
It would appear that the first approach objects while are contain the cell do not actually contain the textblock or the entire cell templated items. It would appear to me there is no way to go from the Border or Rectangle that is clicked, back to the actual text field.
"Long story short" is there ANY way to make this connection?
(Btw I am not willing to give up this ListView/GridView because its payoffs far outweigh this negative and I'd gladly give up on this idea to keep the rest).
I think you sjould be able to either
1) Add some kind of (toggle)button to the root of your data template, and either bind to Command and handle it on your viewmodel or bind to IsChecked/IsPressed and handle changes via data triggers or w/e on the view side.
2) Add EventTrigger to your datatemplate at some point, and handle PreviewNouseUp/Down events there via simple animations.
I'm using this snippet to analyze the rows I've selected on a datagrid.
for (int i = 0; i < dgDetalle.Items.Count; i++)
{
DataGridRow row = (DataGridRow)dgDetalle.ItemContainerGenerator.ContainerFromIndex(i);
FrameworkElement cellContent = dgDetalle.Columns[0].GetCellContent(row);
// ... code ...
}
The cycle runs smoothly, but when processing certain indexes, the second line throws a null exception. MSDN's documentation says that ItemContainerGenerator.ContainerFromIndex(i) will return null if 'if the item is not realized', but this doesn't help me to guess how could I get the desired value.
How can I scan all the rows? Is there any other way?
UPDATE
I'm using this snippet to read a CheckBox as explained here. So I can't use binding or ItemSource at all unless I change a lot of things. And I cannot. I'm doing code maintenance.
Try this,
DataGridRow row = (DataGridRow)grid.ItemContainerGenerator.ContainerFromIndex(index);
if (row == null)
{
grid.UpdateLayout();
grid.ScrollIntoView(grid.Items[index]);
row = (DataGridRow)grid.ItemContainerGenerator.ContainerFromIndex(index);
}
The DataGrid is virtualizing the items, the respective rows (i.e. containers) are only created when the row is in view.
You could either turn off virtualization (which makes the first time loading very slow if you have many items, also the memory usage will be higher) or you just iterate over the data and check the values of the data objects' properties which should be bound to the data-grid. Usually you should not need the UI elements at all...
Use this subscription:
TheListBox.ItemContainerGenerator.StatusChanged += (sender, e) =>
{
TheListBox.Dispatcher.Invoke(() =>
{
var TheOne = TheListBox.ItemContainerGenerator.ContainerFromIndex(0) as ListBoxItem;
if (TheOne != null)
// Use The One
});
};
In addition to other answers: items aren't available in constructor of the control class (page / window / etc).
If you want to access them after created, use Loaded event:
public partial class MyUserControl : UserControl
{
public MyUserControl(int[] values)
{
InitializeComponent();
this.MyItemsControl.ItemsSource = values;
Loaded += (s, e) =>
{
for (int i = 0; i < this.MyItemsControl.Items.Count; ++i)
{
// this.MyItemsControl.ItemContainerGenerator.ContainerFromIndex(i)
}
};
}
}
In my case grid.UpdateLayout(); didn't help an I needed a DoEvents() instead:
DataGridRow row = (DataGridRow)grid.ItemContainerGenerator.ContainerFromIndex(index);
if (row == null)
{
WPFTools.DoEvents();
grid.ScrollIntoView(grid.Items[index]);
row = (DataGridRow)grid.ItemContainerGenerator.ContainerFromIndex(index);
}
/// <summary>
/// WPF DoEvents
/// Source: https://stackoverflow.com/a/11899439/1574221
/// </summary>
public static void DoEvents()
{
var frame = new DispatcherFrame();
Dispatcher.CurrentDispatcher.BeginInvoke(DispatcherPriority.Background,
new DispatcherOperationCallback(
delegate (object f)
{
((DispatcherFrame)f).Continue = false;
return null;
}), frame);
Dispatcher.PushFrame(frame);
}