I am working on a user control which contains a SpinEdit (numeric up-down) control and a ComboBoxEdit. The option selected in the combo-box provides a factor by which number in the SpinEdit is multiplied. At the moment, I have something like this:
public class MyUserControl : DevExpress.XtraEditors.XtraUserControl
{
private static List<String> listItems;
static MyUserControl() // Populate the list of options with the default options
{
listItems = new List<String?();
listItems.Add("Option1");
listItems.Add("Option2");
listItems.Add("Option3");
}
public MyUserControl()
{
InitializeComponent();
// Add default options to the combo box
foreach (String item in listItems)
{
this.cboBox.Properties.Items.Add(item);
}
}
}
That works fine (note that the above is simplified, in reality the static list is a static Dictionary which maps the strings to the multiplication factor) except that I want to allow the user to add custom options to listItems and have these appear on every instance of this user control in my application. That is why listItems is static, as my hope was to do this.cboBox.Properties.Items = listItems; so that any additions to listItems would appear on every control. However, the Items property is read-only so I cannot do that.
How can I go about ensuring every instance of my user control has the same set of options, even if these are changed? Having the static members fire an event when the user changes the option list might do the trick, but that seems a bit overkill for something that looks as simple as this. Does anyone have any other ideas?
In your case is better to use LookUpEdit control instead of ComboBoxEdit. Just make some adjustments to it:
lookUpEdit1.Properties.ShowHeader = false;
You can use your listItems in that way:
lookUpEdit1.Properties.DataSource = listItems;
But there is some problem with Dictionary as DataSource. For DataSource you must use an collection that implements IList, ITypedList or IBindingList interface. So, you can convert your Dictionary to List or you can use this trick:
private static Dictionary<int, string> items;
//...
lookUpEdit1.QueryPopUp += lookUpEdit_QueryPopUp;
lookUpEdit2.QueryPopUp += lookUpEdit_QueryPopUp;
//...
private void lookUpEdit_QueryPopUp(object sender, CancelEventArgs e)
{
var lookUpEdit = (LookUpEdit)sender;
lookUpEdit.Properties.DataSource = null;
lookUpEdit.Properties.DataSource = items;
}
But I think is better to use List instead of Dictionary.
I don't know about the DevExpress controls (you might want to ask on their support forums), but in classic Windows comboboxes, the list is maintained inside the control. The Items property is a .Net wrapper that makes the internal structure easier to work with. So, it's not possible to assign the same data structure to each combobox. They have their own copy.
Your idea to have a publish/subscribe mechanism to what are now static lists seems like a reasonable solution.
If it were me, instead of having static stuff on the control class, I'd make that master list container a separate class and have a property on the control that takes an instance of that class. It'd make your overall architecture a bit more flexible and testable.
Related
I have to create a small WPF/MVVM based GUI that shows the user a list of objects that I get from an external library. The user cannot directly edit those objects, but only select them for further usage.
At first I though I could directly use the given objects in a regular collection as I did not see any need for an INotifyPropertyChanged implementation, but then I noticed that I would need an IsSelected property so that the view model would know which objects are selected by the user and furthermore there is also one case where I have to select specific objects from the view model. This means I have to somehow add the said IsSelected property to make this scenario work in MVVM.
What options do I have?
Do I have to write a wrapper class that inherits from the external class and only extends it by the said IsSelected Property? This would mean I would also have to convert the list of objects that I get from the external library before I can use them.
Or is there maybe a more convenient way to extend the external object so that I can handle the selection in an MVVM based way?
You can define a collection of the selected objects on your viewmodel, like:
public class YourViewModel
{
public List<Thing> SelectedThings { get; } = new List<Thing>();
}
Because the SelectedItems property of the built-in WPF ListBox is not a DependencyProperty so it cannot be bound, you can manage your collection with a simple event handler like
<ListBox SelectionChanged="ListBox_SelectionChanged" />
in codebehind:
private YourViewModel vm;
private void ListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
foreach (var item in e.AddedItems)
{
vm.SelectedThings.Add(item);
}
foreach (var item in e.RemovedItems)
{
vm.SelectedThings.Remove(item);
}
}
If you want to set the selected items from the view model, too, I have found a good solution instead of event handler here: https://www.tyrrrz.me/Blog/WPF-ListBox-SelectedItems-TwoWay-binding
I have the TreeView with objects. When I select item of these tree, than other control - ListView displays as its items properties of selected object. I want to save values of properties when in TreeView selection is change to other object.
So, is there a good way in WPF to gets values of "just before changing" items in ListView control? My idea for now is to override the PreviewMouseDown to check if user click tree node. By god way I mean better than mine. Maybe something in ListView template?
Indication that there is no need to change my idea with the PreviewMouseDown will be also good answer.
Could you please provide the relevant code snippets? I try to answer your question, but I'm not sure I understood it correctly.
If you bind the SelectedItem of you TreeView to a property (a.e. using MVVM pattern), you can save the values before actually setting the item.
Doing so in the setter is not so good though, because it becomes quite large then. I would have a setter like this:
private Foo bar;
public Foo Bar
{
get { return bar; }
set
{
OnPropertyChanging("Bar");
bar=value;
OnPropertyChanged("Bar");
}
}
Then you can listen to your own PropertyChanging events and do your stuff there:
private void this_PropertyChanging(object param, PropertyChangingEventArgs e)
{
switch(e.PropertyName)
{
case "Bar":
//Do you stuff
break,
}
}
I am trying to implement bread crumb navigation. I have a string array in the C# code like this:
public static readonly BindableProperty CurrentPathProperty =
BindableProperty.Create<FileBrowser, string[]>(c => c.CurrentPath, null);
public string[] CurrentPath
{
get { return GetValue(CurrentPathProperty) as string[]; }
set { SetValue(CurrentPathProperty, value); }
}
What would be the correct way to bind to the property in XAML (display the bread crumbs and update CurrentPath when one of them is tapped)? I've tried googling ListViews and x:Array but don't see a straightforward way to do this. I know I need a PropertyChanged event handler but it's not clear to me what needs to happen on the XAML side or what the handler would look like.
If you want your control to update itself when items are added to your array, you should use something implementing INotifyCollectionChanged, like ObservableCollection instead of an array.
With that as source, you can bind it to the ItemSource of a ListView; the ListView being the only Xamarin.Forms controls that supports DataTemplating out of the box.
Anything more complex require defining your own control, inheriting e.g. from StackLayout or any other Layout, and handle creating a Label for each of the string added to your array.
I have an overview of some objects, displayed in a listView.
When an object is selected I want to show a form containing more details about the selected item.
public lessonForm(lesson foo)
[get and display data]
[...]
lessonListView.ItemActivate += lessonSelected;
void lessonSelected(object sender, eventArgs e)
{
lesson ??? = //REQUESTION MAGIC here.
new lessonForm(???).Show();
}
Since ListViewItems are acutally just texts and not programmatically connected to the lesson-object I used to create them, I have not found a proper way to find the respective lesson-object for each listViewItem.
Sure I could do
lesson ??? = Program.listOfAllLessons.Find((candidate) => {
return candidate.plainTextName == selectedItem.Text //abbrev. on purpose
});
However I think it is undisputed that that is just horrible code, on more than one level.
Basically:
I would wish for listViewItem to have an
obj underlyingObject;
field that allows for easy access to the object represented by the listViewItem.
Is there a functionality that allows for this?
You could use the Tag property to store the associated object when creating the ListViewItem. As Tag is of type object you'd need to cast it appropriately when you read from it.
I'm a newbie to WPF and C# and am building my first app mostly by using code examples. I'm sure there might be some better ways to do this, that I'm not understanding yet, so I'm coming to you guys for some advice.
I have a treeview control with of a bunch of nested objects that is downloaded into an ObservableCollection viewmodel from a WCF Service that I also built. I have the viewmodel declared in the Windows.Resources of the XAML.
My treeview then binds to that StaticResource by its key name.
Items="{Binding Source={StaticResource MyCatalogModel},Path=Items, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
The data in the tree is saved locally to a file. When the viewmodel is instantiated it reads the file, or it creates it if it doesn't exist.
I have 2 related problems right now.
Sometimes the data object that is imported is rather large with lots of nested objects (children). This is taking a long time to update the tree. How can I speed this up? Can I "turn off" the Notify changed stuff of the ObservableCollection, and just reload (rebind?) the viewmodel when it's finished?
I'd like to give the user the ability to basically clear out all the items from the tree and start from scratch. I have code that dumps the underlying file and as I said, it will be recreated when a new viewmodel is instantiated, but I don't know how to "reset" the binding of the resource and the tree. How do I do this?
Thanks to all who respond and any code snippets will be greatly appreciated!!
I had a similar problem, where I had a very large amount of data in a collection - and the event for OnPropertyChanged was firing for each item in the collection. I added an extension with a method to add a range to an ObservableCollection. Here is the code for the extension.
public class SmartCollection<T> : ObservableCollection<T>
{
public SmartCollection()
: base()
{
_suspendCollectionChangeNotification = false;
}
bool _suspendCollectionChangeNotification;
protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
{
if (!_suspendCollectionChangeNotification)
{
base.OnCollectionChanged(e);
}
}
public void SuspendCollectionChangeNotification()
{
_suspendCollectionChangeNotification = true;
}
public void ResumeCollectionChangeNotification()
{
_suspendCollectionChangeNotification = false;
}
public void AddRange(IEnumerable<T> items)
{
this.SuspendCollectionChangeNotification();
int index = base.Count;
try
{
foreach (var i in items)
{
base.InsertItem(base.Count, i);
}
}
finally
{
this.ResumeCollectionChangeNotification();
var arg = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset);
this.OnCollectionChanged(arg);
}
}
}
So instead of an ObservableCollection its a SmartCollection. What I did was build my collection of objects into a List then you call the AddRange method and pass in your List of objects. This greatly improved the performance.
As far as recreating the tree - if its based on the viewmodel. Just new up the viewmodel that its bound to.
It's amazing how many times the same old questions come up again and again. Right, I have no idea why you are Binding to a StaticResource, but that is a bad idea.
Just create a public property of type ObservableCollection<T> in your view model, set an instance of it as the DataContext of your view in whichever way you prefer or know. Make sure you implement the INotifyPropertyChanged Interface correctly in the code behind, or declare a DependencyProperty instead. Then you can Bind directly to this property, let's call it Items:
<TreeView ItemsSource="{Binding Items}" ... />
When you have it set up this way, then all you need to do to empty or reset the TreeView is this (in the view model):
Items = new ObservableCollection<YourItemDataType>();
As for speed, it's hard to know what you're doing, but WPF is known for being slow when rendering large collections. I can't help with that, sorry.