In datagrid click on cell combobox is (edititemtempalate) not coming

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C#

WPF

Hi All,
I am working on WPF application,Here i am trying to change the value based on combobox selection in datagrid.But if i click on cell(double click or single click) i am not getting the combobox.
I am using the below code.

<DataGrid Grid.Row="1" Grid.Column="3" x:Name="fieldGrid" 
   AutoGenerateColumns="False" GridLinesVisibility="None"  AllowDrop="True" Drop="__fieldGrid_Drop" PreviewDrop="__fieldGrid_PreviewDrop">
 <DataGrid.Columns >
<DataGridTemplateColumn Header="Source Table Columns"  Width="*" 
 CanUserResize="True" IsReadOnly="True" CanUserSort="True" SortMemberPath="ColumnName"
 CellTemplate="{StaticResource DataSourceCellTemplate2}" CellEditingTemplate="{StaticResource EditingDateTemplate}" SortDirection="Ascending"/>
</DataGrid.Column>
 </DataGrid>

and i created CellTemplate and CellEditingTemplate seperately.that code is below.
<datatemplate x:key="DataSourceCellTemplate2">
<stackpanel orientation="Horizontal" margin="1,3">
<textblock name="dsFieldText2" text="{Binding Value}">



<datatemplate x:key="EditingDateTemplate">
<stackpanel orientation="Horizontal" margin="1,3">
<combobox>



If i click on cell even i am not getting empty combobox.
Anyone could you please help me.

What I have tried:

I have been tried so many articles.I have used the below code

<DataGridTemplateColumn Header="">
    <DataGridTemplateColumn.CellEditingTemplate>
        <DataTemplate>
            <ComboBox IsEditable="False" 
                Text="{Binding ComponentIdentifier,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
                ItemsSource="{Binding Path=ApplicableIdentifiers, Mode=OneWay, UpdateSourceTrigger=PropertyChanged}" />
        </DataTemplate>
    </DataGridTemplateColumn.CellEditingTemplate>
    <DataGridTemplateColumn.CellTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding ComponentIdentifier}" />
        </DataTemplate>
    </DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>

If i used this code the i am getting this error edititem is not allowed for this view in wpf datagrid