Develop Reference

WPF: Content of textbox/Combobox goes beyond window screen

I have a textbox/combobox displaying a particular path and both the textbox and combobox are already set to change size according to their contents. If the path is very long, it goes beyond the window screen and the "browse button" I have given gets hidden.(refer image for clarity).Note:I have this problem for both text & comboboxes.
Here's the snippet of a particular case:
<Label Content="_Layout Report Output Path:" Grid.Row="5" Target="{Binding ElementName=TxtLytRepPath}"/>
<StackPanel Grid.Row="5" Grid.Column="1" Orientation="Horizontal">
<ComboBox Name="CmbLytRepPath" Grid.Column="1" Text="{Binding LayoutReportPath, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" IsEditable="True" IsReadOnly="True"/>
<Button Name="BtnLytRepPath" Style="{StaticResource BrowseButton}"/>
</StackPanel>
</Label>
Button Style:
<Style TargetType="Button" x:Key="BrowseButton">
<Setter Property="Content" Value="..."/>
<Setter Property="VerticalAlignment" Value="Center"/>
<Setter Property="HorizontalAlignment" Value="Center"/>
<Setter Property="Margin" Value="2"/>
<Setter Property="MinHeight" Value="23"/>
<Setter Property="Width" Value="40"/>
</Style>
I cannot use a wrap panel as its makes the UI bad.Please suggest me some solution.

In your example, you close twice the label.
I think you will try with a dockpanel
<DockPanel Grid.Row="5" Height="??? if need">
<Label DockPanel.Dock="Left" Content="_xxx"/>
<Button DockPanel.Dock="Right" Style=” ”/>
<ComboBox />
</DockPanel>
Regards

Windows 8 metro app: styling a button dynamically. C# and Xaml

I have a xaml page with Gridview which has a Button.I am using a grouped Item page. The buttons are generated based on the dataset returned.
10 records will display 10 buttons.
<GridView.ItemTemplate>
<DataTemplate>
<Grid HorizontalAlignment="Left" Width="Auto" Height="Auto" >
<Button Click="ItemView_ItemClick">
<StackPanel Margin="5" >
<TextBlock Tag="cntCustName" Style="{ThemeResource CntNormalTextBlockStyle}" Text="{Binding CUSTOMERNAME }"/>
<TextBlock Tag="cntCatCode" Style="{ThemeResource CntLrgTextBlockStyle}" Text="{Binding CATEGORYCODE}"/>
<TextBlock Tag="cntDay" Style="{ThemeResource CntNormalTextBlockStyle}" Text="{Binding DAY}"/>
</StackPanel>
</Button>
</Grid>
</DataTemplate>
</GridView.ItemTemplate>
I am getting data in a foreach loop. I want to be able to assign the styles of the buttons
dynamically based on some criteria which I have.
foreach (ContactData ContactData in _openContatcs)
{
if (ContactData.CFLAG)
{
//this is an example
Application.Current.Resources["contactSquare"] = ampStyle;
}
group.Items.Add(ContactData);
}
Styles are defined like this in a folder: Assests/Resources/BaseAPStyles.xaml
<Style x:Name="contactSquare" TargetType="Button">
<Setter Property="BorderBrush" Value="Transparent"/>
<Setter Property="BorderThickness" Value="0"/>
<Setter Property="Height" Value="160"/>
<Setter Property="HorizontalAlignment" Value="Left"/>
<Setter Property="Margin" Value="5"/>
<Setter Property="VerticalAlignment" Value="Top"/>
<Setter Property="Width" Value="160"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="Button">
<Grid Background="#ffffc600">
<ContentPresenter>
</ContentPresenter>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
My buttons are not showing the styles. How can I achieve this?

use x:key="contactSqaure" to find the style in the application resources.
Then, access the button you would like to style and assign the style to the button like this.
yourButton.Style = Application.Resources.Current["contactSqaure"] as Style;
You can also define styles in C#, or edit the button's dependency properties.
yourButton.Height = 160;
yourButton.VerticalAlignment = VerticalAlignment.Center;
you can access the button in your datatemplate when it loads.
<DataTemplate>
<Button Loaded="Button_Loaded" .../>
....
void Button_Loaded(object sender, RoutedEventArgs args)
{
(sender as Button).Style = yourStyle;
}

Rude tab keeps coming to the front

I have a TabControl that uses the following XAML.
<TabControl x:Class="MyApp.Tab.TabContainer"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:MyApp.Tab"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300"
ItemsSource="{Binding}">
<TabControl.Resources>
<Style TargetType="TextBox">
<Setter Property="VerticalAlignment" Value="Stretch"></Setter>
<Setter Property="HorizontalAlignment" Value="Stretch"></Setter>
<Setter Property="AcceptsReturn" Value="True"></Setter>
<Setter Property="TextWrapping" Value="WrapWithOverflow"></Setter>
<Setter Property="MaxLines" Value="5000"></Setter>
<Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto"></Setter>
<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"></Setter>
</Style>
<SolidColorBrush x:Key="mouseOverColor" Color="Red"></SolidColorBrush>
<RadialGradientBrush x:Key="glowColor" Center="0.5,0.5" RadiusX="0.5" RadiusY="0.5" GradientOrigin="0.5,0.5">
<GradientStop Color="Red" Offset="0.5"></GradientStop>
</RadialGradientBrush>
<RadialGradientBrush x:Key="glowMask" Center="0.5,0.5" RadiusX="0.5" RadiusY="0.5" GradientOrigin="0.5,0.5">
<GradientStop Color="#80FFFFFF" Offset="0"></GradientStop>
<GradientStop Color="#80FFFFFF" Offset="0.6"></GradientStop>
<GradientStop Color="#00FFFFFF" Offset="1"></GradientStop>
</RadialGradientBrush>
<DataTemplate x:Key="NewTabHeaderTemplate" DataType="{x:Type local:AddNewTab}">
<DockPanel>
<TextBlock Name="TextBlock" VerticalAlignment="Center" Text="+" FontSize="18" MouseLeftButtonDown="TextBlock_OnMouseLeftButtonDown"></TextBlock>
</DockPanel>
</DataTemplate>
<DataTemplate x:Key="MapTabHeaderTemplate" DataType="local:ACTabItemTabItem">
<DockPanel>
<Button Name="btn_TabDelete" DockPanel.Dock="Right" Margin="5,0,0,0" Padding="0" Click="btn_TabDelete_Click" CommandParameter="{Binding RelativeSource={RelativeSource AncestorType={x:Type TabItem}}, Path=Name}">
<Image Source="icon_grey_cross.gif" Height="9" Width="9" Margin="0,0,0,0"></Image>
<Button.Template>
<ControlTemplate TargetType="Button">
<Border x:Name="bdr_main" Margin="4" BorderThickness="0" >
<ContentPresenter VerticalAlignment="Center" HorizontalAlignment="Center" Margin="4,4,4,4" ContentSource="Content" />
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter TargetName="bdr_main" Property="Background" Value="{StaticResource glowColor}"></Setter>
<Setter TargetName="bdr_main" Property="OpacityMask" Value="{StaticResource glowMask}"></Setter>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Button.Template>
</Button>
<TextBlock VerticalAlignment="Center" Text="{Binding RelativeSource={RelativeSource AncestorType={x:Type TabItem}}, Path=Header}"></TextBlock>
</DockPanel>
</DataTemplate>
</TabControl.Resources>
public class AddNewTab : TabItem {}
During the constructor I do this to produce a blank tab with a simple '+' in the header.
_tabItems = new ObservableCollection<ACTabItem>();
try
{
AddNewTab tabAdd = new AddNewTab();
tabAdd.HeaderTemplate = this.FindResource("NewTabHeaderTemplate") as DataTemplate;
_tabItems.Add(tabAdd);
}
this.DataContext = _tabItems;
When the user clicks the '+' I create a new TabItem and add it to the Items collection. I then attempt to bring the new tab to the front. (ImplementTab() simply creates a new TabItem with some values preset by the contents of 'td').
//code up here just collects some data from user to populate 'td'
TabItem newTab = ImplementTab(td);
if (newTab != null)
{
_tabItems.Add((ACTabItem)newTab);
newTab.Focus();
}
If I watch the this_SelectionChanged() event handler I see that the Focus() call does cause a change in SelectedIndex to the index of the newly added tab, but I also see that after the method the new tab code is in completes (right after the Focus()), SelectionChanged is thrown again, but this time with a SelectedIndex of '0' (the original blank tab with the '+' header).
Clicking on a tab throws SelectionChanged only once and I get the expected results.
I am simply trying to have the TabControl focus on a newly added TabItem... how did I mess that up?

I feel that you don't have to inherit your AddNewTab from TabItem if you do databind. It should be just any class, inheriting it from TabItem makes it confusing since TabControl will create a new TabItem to wrap around this data item so all the methods like Focus() on the tab you created will have no effect.
To select the last tab just set the SelectedIndex instead of calling Focus.
if (TabControl1.Items.Count > 0)
TabControl1.SelectedIndex = TabControl1.Items.Count - 1;

Change Images on Custom CheckBox in WPF

All I have created the following custom CheckBox which uses images instead of a CheckBox. This works well however, I want to be able to change the images as required. Ideally I would like to use application resources Properties.Resources.SomeImage16 (a .png file). The XAML is
<Style x:Key="styleCustomCheckBox"
TargetType="{x:Type CheckBox}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type CheckBox}">
<StackPanel Orientation="Horizontal">
<Image x:Name="imageCheckBox"
Width="16"
Height="16"
Source="F:\Camus\ResourceStudio\Graphics\Images\UnPinned16.png"/>
<ContentPresenter VerticalAlignment="Center"/>
</StackPanel>
<ControlTemplate.Triggers>
<Trigger Property="IsChecked" Value="False">
<Setter TargetName="imageCheckBox"
Property="Source"
Value="F:\Camus\ResourceStudio\Graphics\Images\Pinned16.png"/>
</Trigger>
<Trigger Property="IsChecked" Value="True">
<Setter TargetName="imageCheckBox"
Property="Source"
Value="F:\Camus\ResourceStudio\Graphics\Images\UnPinned16.png"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
With implementation
<ListBox SelectionMode="Single" >
<StackPanel Orientation="Horizontal">
<CheckBox Style="{StaticResource styleCustomCheckBox}"
HorizontalAlignment="Left"
VerticalAlignment="Center"
Margin="4,0,4,0"/>
<TextBlock VerticalAlignment="Top"
Text="SomeRecentDocument.resx"/>
</StackPanel>
</ListBox>
How can I change the images used for the custom CheckBox (i.e. change the pinned/un-pinned to tick/cross etc.) without having to create a new style/template?
Thanks for your time.

As already mentioned #HighCore the need for the ability to use vector graphics. In this case, to use the Path, where in Data to the specified coordinates on which the object is drawn (MSDN).
Advantages:
Do not store it in the files, smaller size
Dynamically changing color, size and the whole shape
Minuses (in my opinion):
You can not always find the right Data for the Path
About minus: There are special sites (www.modernuiicons.com) and utilities for converting the image to Data.
Change the style of CheckBox using the Path:
Style
<Style x:Key="styleCustomCheckBox" TargetType="{x:Type CheckBox}">
<Setter Property="FontFamily" Value="Verdana" />
<Setter Property="FontSize" Value="14" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type CheckBox}">
<StackPanel Orientation="Horizontal">
<Path x:Name="MyPin" Width="18" Height="18" Stretch="Fill" Fill="#FF000000"
Data="F1 M 56.1355,32.5475L 43.4466,19.8526C 42.7886,20.4988 42.298,21.2123 41.9749,21.9932C 41.6519,22.7741 41.4903,23.5729 41.4903,24.3895C 41.4903,25.1942 41.6529,25.987 41.9779,26.7679L 34.0577,34.6821C 33.3918,34.3372 32.6991,34.0776 31.9796,33.9032C 31.2601,33.7288 30.5298,33.6415 29.7885,33.6415C 28.623,33.6415 27.4953,33.8526 26.4052,34.2748C 25.315,34.697 24.3419,35.3342 23.4856,36.1865L 30.2344,42.9174L 25.9027,47.9032L 22.6532,51.8425L 20.5988,54.5836C 20.1212,55.2892 19.8823,55.753 19.8823,55.975L 19.8645,56.0701L 19.9002,56.088L 19.9002,56.1474L 19.9358,56.1058L 20.0131,56.1236C 20.2351,56.1236 20.6989,55.8888 21.4045,55.419L 24.1457,53.3765L 28.0849,50.1151L 33.0945,45.7775L 39.8016,52.5025C 40.6579,51.6462 41.2961,50.6731 41.7163,49.5829C 42.1365,48.4928 42.3466,47.367 42.3466,46.2056C 42.3466,45.4603 42.2603,44.729 42.0879,44.0115C 41.9155,43.294 41.6548,42.6003 41.3069,41.9304L 49.2202,34.0161C 50.0011,34.3372 50.7939,34.4978 51.5986,34.4978C 52.4192,34.4978 53.2189,34.3362 53.9979,34.0132C 54.7768,33.6901 55.4894,33.2015 56.1355,32.5475 Z "/>
<ContentPresenter VerticalAlignment="Center" Margin="10,0,0,0" />
</StackPanel>
<ControlTemplate.Triggers>
<Trigger Property="IsChecked" Value="False">
<Setter TargetName="MyPin" Property="Data" Value="F1 M 32.3691,30.2225L 33.2253,29.3901L 15.361,11.5258C 13.9814,12.7067 12.6951,13.9936 11.5148,15.3738L 26.6252,30.4842C 27.743,30.1631 28.8767,30.0025 30.0263,30.0025C 30.8191,30.0025 31.6,30.0759 32.3691,30.2225 Z M 45.5039,49.3629L 60.6292,64.4826C 62.0123,63.2996 63.3017,62.0101 64.4846,60.6268L 46.6218,42.7866L 45.7834,43.619L 45.9439,44.7726L 45.9915,45.9261L 45.8785,47.6713L 45.5039,49.3629 Z M 56.1355,32.5475L 43.4466,19.8526C 42.7886,20.4987 42.298,21.2123 41.9749,21.9932C 41.6519,22.7741 41.4903,23.5729 41.4903,24.3895C 41.4903,25.1942 41.6529,25.987 41.9779,26.7679L 34.0577,34.6821C 33.3918,34.3372 32.6991,34.0776 31.9796,33.9032C 31.2601,33.7288 30.5298,33.6415 29.7885,33.6415C 28.623,33.6415 27.4953,33.8526 26.4052,34.2748C 25.315,34.697 24.3419,35.3342 23.4856,36.1865L 30.2344,42.9174L 25.9027,47.9032L 22.6532,51.8425L 20.5988,54.5836C 20.1212,55.2892 19.8823,55.753 19.8823,55.975L 19.8645,56.0701L 19.9002,56.0879L 19.9002,56.1474L 19.9358,56.1058L 20.0131,56.1236C 20.2351,56.1236 20.6989,55.8888 21.4045,55.419L 24.1457,53.3765L 28.0849,50.1151L 33.0945,45.7775L 39.8016,52.5025C 40.6579,51.6462 41.2961,50.6731 41.7163,49.5829C 42.1365,48.4928 42.3466,47.367 42.3466,46.2056C 42.3466,45.4603 42.2603,44.729 42.0879,44.0115C 41.9155,43.294 41.6548,42.6003 41.306,41.9304L 49.2202,34.0161C 50.0011,34.3372 50.7939,34.4978 51.5986,34.4978C 52.4192,34.4978 53.219,34.3362 53.9979,34.0132C 54.7768,33.6901 55.4894,33.2015 56.1355,32.5475 Z " />
<Setter TargetName="MyPin" Property="Fill" Value="Gray" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
Using
<StackPanel Orientation="Vertical" HorizontalAlignment="Center">
<CheckBox Height="35"
Style="{StaticResource styleCustomCheckBox}"
Content="MySolution1" />
<CheckBox Height="35"
Style="{StaticResource styleCustomCheckBox}"
Content="MySolution2" />
</StackPanel>
Output
We can also store the Path's in resources, and refer to them as like this:
<Path x:Key="MyPath" Data="F1 M 38,19C 48.4934,19 57,27.5066 ... />
...
<Setter TargetName="MainPath" Property="Data"
Value="{Binding Source={StaticResource MyPath}, Path=Data}" />
Edit
To specify arbitrary icons, I created two attached dependency properties (string type):
IsCheckedOnData
IsCheckedOffData
IsCheckedOnData contains Data value by IsChecked = "True", IsCheckedOffData value by IsChecked = "False".
Now you need only to determine the strings of icons and define such a resource (for example).
Full example:
XAML
<Window x:Class="CustomCheckBoxHelp.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:CustomCheckBoxHelp"
xmlns:sys="clr-namespace:System;assembly=mscorlib"
WindowStartupLocation="CenterScreen"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<sys:String x:Key="Up">
F1 M 37.8516,35.625L 34.6849,38.7917L 23.6016,50.2708L
23.6016,39.9792L 37.8516,24.9375L 52.1016,39.9792L 52.1016,
50.2708L 41.0182,38.7917L 37.8516,35.625 Z
</sys:String>
<sys:String x:Key="Down">
F1 M 37.8516,39.5833L 52.1016,24.9375L 52.1016,35.2292L
37.8516,50.2708L 23.6016,35.2292L 23.6016,24.9375L 37.8516,39.5833 Z
</sys:String>
<Style x:Key="styleCustomCheckBox" TargetType="{x:Type CheckBox}">
<Setter Property="FontFamily" Value="Verdana" />
<Setter Property="FontSize" Value="14" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type CheckBox}">
<StackPanel Orientation="Horizontal">
<Path x:Name="MyPin" Width="18" Height="18" Stretch="Fill" Fill="#FF000000"
Data="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(local:CustomCheckBoxClass.IsCheckedOnData)}" />
<ContentPresenter VerticalAlignment="Center" Margin="10,0,0,0" />
</StackPanel>
<ControlTemplate.Triggers>
<Trigger Property="IsChecked" Value="False">
<Setter TargetName="MyPin" Property="Data"
Value="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(local:CustomCheckBoxClass.IsCheckedOffData)}" />
<Setter TargetName="MyPin" Property="Fill" Value="Gray" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<Grid>
<StackPanel Orientation="Vertical" HorizontalAlignment="Center" Background="Beige">
<CheckBox Height="35"
local:CustomCheckBoxClass.IsCheckedOnData="{StaticResource Up}"
local:CustomCheckBoxClass.IsCheckedOffData="{StaticResource Down}"
Style="{StaticResource styleCustomCheckBox}"
Content="MySolution1" />
<CheckBox Height="35"
local:CustomCheckBoxClass.IsCheckedOnData="{StaticResource Up}"
local:CustomCheckBoxClass.IsCheckedOffData="{StaticResource Down}"
Style="{StaticResource styleCustomCheckBox}"
Content="MySolution2" />
</StackPanel>
</Grid>
</Window>
Code behind
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
}
public class CustomCheckBoxClass : DependencyObject
{
#region IsCheckedOnDataProperty
public static readonly DependencyProperty IsCheckedOnDataProperty;
public static void SetIsCheckedOnData(DependencyObject DepObject, string value)
{
DepObject.SetValue(IsCheckedOnDataProperty, value);
}
public static string GetIsCheckedOnData(DependencyObject DepObject)
{
return (string)DepObject.GetValue(IsCheckedOnDataProperty);
}
#endregion
#region IsCheckedOffDataProperty
public static readonly DependencyProperty IsCheckedOffDataProperty;
public static void SetIsCheckedOffData(DependencyObject DepObject, string value)
{
DepObject.SetValue(IsCheckedOffDataProperty, value);
}
public static string GetIsCheckedOffData(DependencyObject DepObject)
{
return (string)DepObject.GetValue(IsCheckedOffDataProperty);
}
#endregion
static CustomCheckBoxClass()
{
PropertyMetadata MyPropertyMetadata = new PropertyMetadata(string.Empty);
IsCheckedOnDataProperty = DependencyProperty.RegisterAttached("IsCheckedOnData",
typeof(string),
typeof(CustomCheckBoxClass),
MyPropertyMetadata);
IsCheckedOffDataProperty = DependencyProperty.RegisterAttached("IsCheckedOffData",
typeof(string),
typeof(CustomCheckBoxClass),
MyPropertyMetadata);
}
}
Note: In the style I have not used TemplateBinding because TemplateBinding doesn’t work outside a template or outside its VisualTree property, so you can’t even use TemplateBinding inside a template’s trigger. Therefore, we must use the construction {RelativeSource TemplatedParent} and a Path equal to the dependency property whose value you want to retrieve.

Sorry, I don't yet know how to reference an image in those resources, but if you can add the images into a folder named Images in your application root directory, then you will be able to reference the images simply like this:
<Image Source="/ApplicationName;component/Images/SomeImage16.png" />

As you mention you can change the checkbox trigger by checked and unchecked. And the image will display corresponding trigger. Your xml code is good for me.I just remove the trigger true portion.because the false portion by default in focus and after click the checkbox image UnPinned16.png is visible. And agan click image Pinned16.png is visibale .
<Style x:Key="styleCustomCheckBox"
TargetType="{x:Type CheckBox}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type CheckBox}">
<StackPanel Orientation="Horizontal">
<Image x:Name="imageCheckBox"
Width="16"
Height="16" Source="F:\Camus\ResourceStudio\Graphics\Images\UnPinned16.png"/>
<ContentPresenter VerticalAlignment="Center"/>
</StackPanel>
<ControlTemplate.Triggers>
<Trigger Property="IsChecked" Value="False">
<Setter TargetName="imageCheckBox"
Property="Source"
Value="F:\Camus\ResourceStudio\Graphics\Images\Pinned16.png"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
And I am using this checkbox under a textblock
<CheckBox Style="{StaticResource styleCustomCheckBox}"
HorizontalAlignment="Left"
VerticalAlignment="Center"
Margin="4,0,4,0"/>

Custom ListBox in WPF

I am trying to create a custom ListBox control in WPF for a chat Messenger. I am using an ellipse to show the online/offline user. The ellipse is to be displayed on left and some text in center of the ListBoxItem.
I want to set the ellipse fill propert to red/green based on some variable.
This is what I have done :
<ListBox Name="myList" HorizontalAlignment="Left" Height="232" Margin="117,74,0,0" VerticalAlignment="Top" Width="207">
<ListBox.ItemTemplate>
<DataTemplate>
<DockPanel>
<Ellipse Name="ellipse" Fill="Red" DockPanel.Dock="Left">
<Ellipse.Triggers>
<Trigger Property="{Binding Online}" Value="True">
<Setter TargetName="ellipse" Property="Ellipse.Fill" Value="Green"/>
</Trigger>
</Ellipse.Triggers>
</Ellipse>
<TextBlock Text="{Binding text}"></TextBlock>
</DockPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
and in the code :
myList.Items.Add(new { text="Hello",Online="True" });
I am getting an error as
Cannot find the static member 'FillProperty' on the type 'ContentPresenter'.
What am I doing wrong here?

Obviously this is wrong: Property="{Binding Online}"
Also you should use a Style for triggers, no need to set TargetName, and you need to take precedence into consideration, and use a Setter for the default value.

you are actually misleading WPF with some of these concerns.
Binding A property on trigger will not work. you have to use DataTrigger insteed of Triggers.
Implementing Trigger on the Fly for any control. most of the times not work. So go with Styles.
While you are creating Ellipse in template make sure you have created enough size for it. So that can be visible to users.
try this.
<Window.Resources>
<Style x:Key="elstyle" TargetType="Ellipse">
<Setter Property="Height" Value="5"/>
<Setter Property="Width" Value="5"/>
<Setter Property="Fill" Value="Red"/>
<Style.Triggers>
<DataTrigger Binding="{Binding Online}" Value="true">
<Setter Property="Fill" Value="Green"/>
</DataTrigger>
</Style.Triggers>
</Style>
</Window.Resources>
<Grid>
<ListBox x:Name="myList" HorizontalAlignment="Left" Height="232" Margin="117,74,0,0" VerticalAlignment="Top" Width="207">
<ListBox.ItemTemplate>
<DataTemplate>
<DockPanel>
<Ellipse Name="ellipse" Margin="5" DockPanel.Dock="Left" Style="{DynamicResource elstyle}">
</Ellipse>
<TextBlock Text="{Binding Name}"></TextBlock>
</DockPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</Grid>
code behind .
public MainWindow()
{
Random r = new Random();
InitializeComponent();
for (int i = 0; i < 10; i++)
{
myList.Items.Add(new { Name = "Name" + i.ToString(), Online = Convert.ToBoolean(r.Next(-1, 1)) });
}
}

You need to set the initial colour via a Setter and not in XAML. For more information and see this question: Change the color of ellipse when mouse over

there are a few issues in your XAML
set the size of your Ellipse
you need to use Style instead of Ellipse.Triggers
set your Fill color in your Style if you wane be able to change it in XAML by some condition
here an working example for your problem
<DataTemplate>
<!--<DockPanel> juste because i like StackPanel-->
<StackPanel Orientation="Horizontal">
<!--<Ellipse Name="ellipse" Fill="Red" DockPanel.Dock="Left">-->
<Ellipse Name="ellipse" Width="15" Height="15">
<!--<Ellipse.Triggers>-->
<Ellipse.Style>
<Style TargetType="Ellipse">
<Setter Property="Fill" Value="Red"/>
<Style.Triggers>
<!--<Trigger Property="{Binding Online}" Value="True">-->
<DataTrigger Binding="{Binding Online}" Value="True">
<Setter Property="Fill" Value="LimeGreen"/>
</DataTrigger>
</Style.Triggers>
</Style>
</Ellipse.Style>
</Ellipse>
<TextBlock Text="{Binding text}"/>
</StackPanel>
</DataTemplate>