Develop Reference

Set combobox Item in code Behind UWP

I have seen how to select the item from the index by code behind, but how can i select it from code behind knowing the string of the item?
combobox code xaml:
<ComboBox x:Name="ComboBoxOne" VerticalAlignment="Center" HorizontalAlignment="Center" Height="40" Width="200">
<ComboBoxItem Content="blue"/>
<ComboBoxItem Content="red"/>
<ComboBoxItem Content="green"/>
</ComboBox>
combobox code behind:
ComboBoxOne.SelectedIndex = 1;
But how to select the item knowing for example green? Is possible?
I tried with ComboBoxOne.PlaceholderText
ComboBoxOne.PlaceholderText="green"
But then I can not use the selecteditem.
Thanks in advance!

First you need to get the Items of the ComboBox as a List to find the Index of the item that you want to select by string. Since this will be a List<String> you can do something like below.
List<String> lstItems = ComboBoxOne.Items
.Cast<ComboBoxItem>()
.Select(item => item.Content.ToString())
.ToList();
and then you can get the index using Linq and assign it to Selected Index. Like below.
ComboBoxOne.SelectedIndex = lstItems.FindIndex(a => a.Equals("green"));
Good Luck.

WPF, Listbox items as source to other Listbox

Let's say you have one Listbox in WPF with items such as 1,2,3,4,5 etc. How do you make another Listbox, right next to first one, that shows its items according to selection in the first Listbox? So if you select "item 2" in Listbox you'd get 2A, 2B,2C etc in Listbox2, if you select "item 3" you'd get 3A, 3B, 3C etc in Listbox3
Can't embed the picture yet but here's the example of what i need

There is an example of how to implement such cascading ComboBoxes according to the recommended MVVM design pattern available here: https://blog.magnusmontin.net/2013/06/17/cascading-comboboxes-in-wpf-using-mvvm/
You could bind the SelectedItem property of the first ListBox to a source property of your view model. In the setter of this one you then set another collection property that you bind the ItemsSource property of the second ListBox to, e.g.:
<ListBox ItemsSource="{Binding Numbers}" SelectedItem="{Binding SelectedNumber}" />
<ListBox ItemsSource="{Binding SubNumbers}" />
private object _selectedNumber;
public object SelectedNumber
{
get { return _selectedNumber; }
set
{
_selectedNumber = value;
NotifyPropertyChanged();
//set items
SubNumbers = new List<string> { "3A", "3B", "..." };
NotifyPropertyChanged("SubNumbers");
}
}
Make sure that your view model class implements the INotifyPropertyChanged interface and raises change notifications for this to work: https://msdn.microsoft.com/en-us/library/system.componentmodel.inotifypropertychanged(v=vs.110).aspx
Alternatively, if your model classes are defined in such a way that each item in the first ListBox has a collection property that returns its related items, you could bind the second ListBox directly to a property of the SelectedItem in the first one:
<ListBox x:Name="lb1" ItemsSource="{Binding Numbers}"/>
<ListBox x:Name="lb2" ItemsSource="{Binding SelectedItem.SubProperty, ElementName=lb1}" />

Set an item on a WPF Combobox when ItemSource is binded to an Enum

I am having trouble assigning the a combobox item by using an enum value that the combobox source is assigned to.
The XAML
<ComboBox HorizontalAlignment="Left"
x:Name="cmbName"
VerticalAlignment="Top"
Width="120" Margin="79,48,0,0">
<ComboBox.ItemsSource>
<CompositeCollection>
<ListBoxItem Content="Please Select"/>
<CollectionContainer Collection="{Binding Source={StaticResource Enum}}" />
</CompositeCollection>
</ComboBox.ItemsSource>
</ComboBox>
The C# that is trying to set the combobox to an item in the enum
// The problem, the assignment doesn't work.
cmbName.SelectedItem = Enum.value;
I can only set a item by using the combobox SelectedIndex
cmbName.SelectedIndex = 2;
But this is hardcoding the index so if the enum changes, so will the value.
So how can I set the combobox by the enum value?
Thanks

It's very hard to tell what your problem is because you haven't fully documented your scenario. As such, all that I can do is to show you how to do what you want. As I prefer to work with properties, I won't be using any Resources for this example, but I'm sure that you'll still be able to relate this solution to your problem.
So, first we have a test enum and some properties and some initialisation:
public enum TestEnum
{
None, One, Two, Three
}
private TestEnum enumInstance = TestEnum.None;
public TestEnum EnumInstance
{
get { return enumInstance; }
set { enumInstance = value; NotifyPropertyChanged("EnumInstance"); }
}
private ObservableCollection<TestEnum> enumCollection = new ObservableCollection<TestEnum>() { TestEnum.None, TestEnum.One, TestEnum.Two, TestEnum.Three };
public ObservableCollection<TestEnum> EnumCollection
{
get { return enumCollection; }
set { enumCollection = value; NotifyPropertyChanged("EnumCollection"); }
}
...
EnumCollection.Add(TestEnum.One);
EnumCollection.Add(TestEnum.Two);
EnumCollection.Add(TestEnum.Three);
EnumInstance = TestEnum.Three;
Then we have a ComboBox:
<ComboBox Name="ComboBox" ItemsSource="{Binding EnumCollection}"
SelectedItem="{Binding EnumInstance}" />
If you run the application, then at this point the selected ComboBoxItem should read Three. Because the ComboBox.SelectedItem is data bound to the EnumInstance property, setting...:
EnumInstance = TestEnum.Two;
... is roughly the same as:
ComboBox.SelectedItem = TestEnum.Two;
Both of these would select the Two value in the ComboBox. However, note this example:
EnumInstance = TestEnum.None;
Setting either the EnumInstance or the ComboBox.SelectedItem property to TestEnum.None would have no effect in the UI because there is no TestEnum.None value in the data bound collection.

I apologise that my answer was descriptive enough, however, the reason why I haven't set my enum as a property as Sheridan has described below is that I need an extra string value in my combo which you can see is "Please Select" and unfortunately, I cannot put this in the enum.
But Sheridan's method and logic is the way to go if you want to do this.
However, for my problem, I simply just used
ComboBox.SelectedValue = Enum.Value.ToString();
Thanks

WPF Unable to set Selected Item of a Combo box

I have a non-bound Combobox and I want to set its value at run time. I tried a lot but cannot achieve it. Here's the code :
<ComboBox Background="#FFB7B39D" Grid.Row="1" Height="23"
HorizontalAlignment="Right" Margin="0,26,136,0"
Name="cboWellDiameter" VerticalAlignment="Top" Width="120">
<ComboBoxItem Content="meter" IsSelected="True" />
<ComboBoxItem Content="centimeter" />
</ComboBox>
In code, I am trying with :
//VALUE of sp.wellborediameterField_unit is centimeter
// Gives -1
int index = cboWellDiameter.Items.IndexOf(sp.wellborediameterField_unit);
Console.WriteLine("Index of well bore dia unit = " + index.ToString());
cboWellDiameter.SelectedIndex = index;
// cboWellDiameter.SelectedItem = sp.wellborediameterField_unit;
// cboWellDiameter.SelectedValue = sp.wellborediameterField_unit;
SelectedItem & selectedValue has no impact. Why its not even able to find in Items ? How do I set it ?
Please help me, have several such non-bound and binded combos to set programmatically.

The issue is that your items are ComboBoxItems, not strings. So you have two options: one, use strings as the combo-box items (this allows you to set SelectedItem / SelectedValue = "meter" or "centimeter"):
<ComboBox xmlns:clr="clr-namespace:System;assembly=mscorlib">
<clr:String>meter</clr:String>
<clr:String>centimeter</clr:String>
</ComboBox>
or two, set the SelectedItem by searching for the appropriate ComboBoxItem:
cboWellDiameter.SelectedItem = cboWellDiameter.Items.OfType<ComboBoxItem>()
.FirstOrDefault(item => item.Content as string == cosp.wellborediameterField_unit);

Can't bind selection to WPF Combobox

I would like to have a ComboBox with two options "M" and "F" and set the selection from my code with a string of one of the values. This seems so basic it's embarassing to even ask. However, I haven't seen a single example that doesn't include 50 lines of code with custom classes, etc, etc. To make things even easier, I want to prefill the two option in my XAML. Why is this simple task making me feel like a mental midget? This is what I have:
<ComboBox x:Name="cboGender" >
<ComboBoxItem Tag="M" Content="M"></ComboBoxItem>
<ComboBoxItem Tag="F" Content="F"></ComboBoxItem>
</ComboBox>
Code Behind:
cboGender.SelectedValue = "M";
Please help before I smash my computer and go back to ASP.NET development forever.

Try the following:
cboGender.ItemsSource = new string [] { "M", "F" };
cboGender.SelectedItem = "M";
You need to set the ItemsSource to the collection of items. The ComboBox will then generate the ComboBoxItems for you.

Add the SelectedValuePath and it works:
<ComboBox x:Name="cboGender" SelectedValuePath="Content" >
<ComboBoxItem Tag="M" Content="M"></ComboBoxItem>
<ComboBoxItem Tag="F" Content="F"></ComboBoxItem>
</ComboBox>
(SelectedValuePath="Tag" would work, too, having the same data in two places seems quite redundant either way though)
As a side-note, similar to Colin's answer you can set the items like this:
xmlns:sys="clr-namespace:System;assembly=mscorlib"
<ComboBox x:Name="cboGender">
<sys:String>M</sys:String>
<sys:String>F</sys:String>
</ComboBox>
(Both SelectedItem and SelectedValue work in this case)

Try this - cboGender.SelectedIndex = 0; before smashing your system.. :)

To a first approximation, if you ever manipulate WPF UI elements in code you're doing it wrong. Sure, you can create a combo box with an "M" and an "F" and preset its selection:
<ComboBox>
<ComboBoxItem>M</ComboBoxItem>
<ComboBoxItem>F</ComboBoxItem>
<ComboBox.SelectedIndex>0</ComboBox.SelectedIndex>
</ComboBox>
But then what? What do you do with that selection? If your answer involves something like this:
if cboGender.SelectedValue == "M"
you're traveling down a road that will lead you to writing programs that are very hard to maintain.
If, on the other hand, you create a class to bind your UI to, like this:
public class MyViewModel
{
public MyViewModelClass()
{
Gender = "M";
}
public IEnumerable<string> Genders { get { return new string[] { "M", "F" } };
public string Gender { get; set; }
}
Then your XAML - assuming that somewhere along the line you've set the DataContext to an instance of MyViewModel - becomes:
<ComboBox ItemsSource="{Binding Genders}" SelectedValue="{Binding Gender}"/>
Any other logic that uses the Gender property now looks at this class, not the UI. So you can change the UI without affecting your logic, and vice versa.
(Note that while view models typically implement INotifyPropertyChanged, you only need to do this if you're going to be changing the Gender in your code and want the new values to be reflected in the UI.)