Is there a way to override the Add() method of Combobx?
The reason I ask this is that I want to Add the class objects to my combbox but for display I want it to show the Name of my objects.
so for example: combbox.Items.Add(myClassObject)
but what we actually see in the combbobx as the user will show as myClassObject.Name
If I right understood your request, you can do that using the binding:
Pseudocode:
comboBox.DataSource = collectionOfData;
comboBox.DisplayMember = "Name";
The data will be added to combo but visualized will be the Name property of the "data".
This all done using DisplayMember Property.
Because ComboBox uses ToString() method of object which is added in Items collections to display on the UI, so override ToString of myClassObject to return whatever you want, it is simple:
class myClassObject
{
public override string ToString()
{
return "whatever you want";
}
}
With this way you do not touch ComboBox Control
You can develop extension Method
public static class Extension
{
public static void Add(this ComboBox, myClassObject value)
{
...
}
}
Create a new control that extends combobox control. Then override Add method.
Related
I need to derive a class from ComboBox and change its Items property. Here is my code:
public class MyComboBox2 : ComboBox
{
private MyObjectCollection MyItems;
public MyComboBox2()
{
MyItems = new MyObjectCollection(this);
}
//new public ComboBox.ObjectCollection Items
new public MyObjectCollection Items
{
get {
return MyItems;
}
}
}
public class MyObjectCollection : ComboBox.ObjectCollection
{
public MyObjectCollection(ComboBox Owner) : base(Owner)
{
}
new public int Add(Object j)
{
base.Add(j);
return 0;
}
}
As you can see, I am creating a new class MyComboBox2 derived from ComboBox. This class is supposed to have a new Items property, which would be of type MyObjectCollection rather than ComboBox.ObjectCollection. I have a comboBox called myComboBox21 on the form of type MyComboBox2. When I want to add a new object to my ComboBox, I would execute code like this: myComboBox21.Items.Add("text");
In this case, I end up executing the Add method of MyObjectCollection that I implemented myself. However, the ComboBox on the form does not end up containing value 'text'. I am attaching screenshot of debugger showing ComboBox values. MyComboBox21 contains Items Property (which does contain "text", as shown in screenshot "2.png"), and it contains base.Items (which does not contain "text" as shown in "1.png"). So, apparently, MyComboBox21 contains its own Items property (which I can insert to), and its base class's Items property, which gets displayed in the Windows Form. What can I do so that I can successfully add to comboBox with my own method? Since my ComboBox has 2 Items properties, can I specify which Items property's values should be shown in ComboBox?
Just by looking very quickly on the code:
The original Item index is declared as
virtual Object this[int index] {...}
Does the new keyword maybe be exchanged by override in your implementation in order to make the runtime pick the intended code?
I have a list that contains custom objects. These objects have different properties, and I have ~100 of them. I want to create a list of them in a listbox, but the listbox displays only
MyNamespace.MyClass
MyNamespace.MyClass
MyNamespace.MyClass
MyNamespace.MyClass
...
Is it possible to make the listbox display a certain value for each item? Lets say my objects have an ID string value. Can I display the ID for each item without discarding my objects' other properties?
I currently fill the listbox this way:
lbox.Items.Clear();
lbox.Items.AddRange(list.ToArray());
Set the DisplayMember to the property of your class that you'd like the user to see.
lbox.Items.Clear();
lbox.Items.AddRange(list.ToArray());
lbox.DisplayMember = "ID"; // ID is a public property in MyClass
Lets say you MyClass looks like this:
public class MyClass
{
public int Id { get; set; }
}
There are two options available.
You can use DataBinding for that.
Set the DisplayMember to the propertie of your MyClass which you would like to display
lbox.DisplayMember = "Id";
Set the items using the DataSource propertie of your ListBox
lbox.DataSource = list.ToArray();
You can simple override the ToString method of your MyClass object and return the text you would like to display.
Override the ToString method of your MyClass
public class MyClass
{
public int Id { get; set; }
public override string ToString()
{
return Id.ToString();
}
}
Set the items the same way as you mentioned
lbox.Items.AddRange(list.ToArray());
More Information
MSDN: ListControl.DisplayMember Property
MSDN: Object.ToString Method
Without discarding the object you can attach the object to the tag after.
list.ToList().ForEach(item => lbox.Items.Add(new ListItem(item.ID){Tag = item});
then to retreive it :
var myitem = ((ListItem)lbox.SelectedItem).Tag as MyClass;
Try using Linq.
lbox.Items.AddRange(list.Select(x => x.ID).ToArray());
Where ID is a property with the value you want to show.
You can also override ToString() in the class.
I have a app that makes use of the PropertyGrid in C#/.NET
the PropertGrid holds onto the MyAppObject class/object shown below..
class MyAppObject
{
private List<MyObject> oItems;
public List<MyObject> Items
{
get { return this.oItems; }
}
}
And so far it works well, nice and simple. I want the property grid to allow users to view the items, which it does well, however when you select the property in the PropertyGrid the dialog also allows to add more List<MyObject> items.
I do not want this, I only want to have the ability to show the items, not edit them.
I thought by not providing the setter (set { this.oItems = value; }):
then it wouldnt allow the add button.
Hope this makes sense, The screenshots shows the dialog, and I circled the buttons I want to remove.
thanks
If you expose it as a read-only list, it should do what you need:
[Browsable(false)]
public List<MyObject> Items
{
get { return this.oItems; }
}
// this (below) is the one the PropertyGrid will use
[DisplayName("Items")]
public ReadOnlyCollection<MyObject> ReadOnlyItems
{
get { return this.oItems.AsReadOnly(); }
}
Note that the members of individual objects (MyObject instances) will still be editable, unless you decorate them as [ReadOnly(true)].
As you note, the setter is not necessary to add/remove/edit items. That is because the grid still has full access to the .Add, .Remove and indexer (list[index]) operations.
This is a slightly tricky one; the solution involves building with the full .NET Framework (since the client-only framework doesn't include System.Design). You need to create your own subclass of CollectionEditor and tell it what to do with the temporary collection after the UI is finished with it:
public class MyObjectEditor : CollectionEditor {
public MyObjectEditor(Type type) : base(type) { }
public override object EditValue(ITypeDescriptorContext context, IServiceProvider provider, object value) {
return ((MyObject)context.Instance).Items;
}
}
Then you have to decorate your property with the EditorAttribute:
[Editor(typeof(MyObjectEditor), typeof(UITypeEditor))]
public List<MyObject> Items{
// ...
}
Reference: What's the correct way to edit a collection in a property grid
Alternative:
return new ReadOnlyCollection(oItems);
OR
return oItems.AsReadOnly();
When I add an item to the CheckedListBox list box I also want to store a reference to another object. I tried adding a new instance of this object to the CheckedListBox.
public class CheckedListBoxExtention : CheckedListBox
{
private ReferenceItem _referenceItem;
public ReferenceItem storedItem
{
get { return _referenceItem; }
set { _referenceItem = value; }
}
public CheckedListBoxExtention(ReferenceItem storedItem)
{
_referenceItem = storedItem;
}
}
This works in that later when I foreach though the items in CheckedListBox I have a reference to the _referenceItem object. However, when I add items like this, CheckedListBox shows up as blank (the list in the GUI itself). So I am trying to find a way to override the item text or something like that.
This is the code I used to fix the problem
class ReferenceItemWrapper
{
private ReferenceItem _item;
public ReferenceItemWrapper(ReferenceItem item)
{
_item = item;
}
public ReferenceItem getItem
{get {return _item;}}
public override string ToString()
{
return _item.ToString();
}
}
I am a bit new to wrappers. Why exactly did it work after it was wrapped when it did not work when I added the ReferenceItem directly to the CheckedListBox?
The CheckedListBox uses the ToString method of the objects in the list to populate the captions in the box. Rather than extend the CheckedListBox, just create a wrapper class that lets you store both your reference and a caption, and implements a ToString method which returns your caption. Just create one of your wrapper objects, stick the text in it, stick your reference in it, then add the wrapper object to the list box.
I have a ListBox which is binded to instance of Class A, which is a collection.
class A : List<B>
{
public override ToString()
{
return "A";
}
}
ListBox:
<ListBox ItemsSource="{Binding instanceOfA}"></ListBox>
When the application is run, every item shows "(Collection)"
What can I do to make each item show "A" instead of "Collection"?
In order do what you are trying to do, you should have something like this
class B
{
public override ToString()
{
return "A";
}
}
The ListBox calls ToString on each item of the collection, that means your method never gets called. You'd need to override the ToString() in B.