[C#][SL][VS 2010] Redimensionnement auto

Bonjour,

j'ai créé une datagrid de cette façon:
Code:
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<Grid x:Name="LayoutRoot" Background="White" Height="662" GotFocus="LayoutRoot_GotFocus">
        <Grid.RowDefinitions>
            <RowDefinition Height="80"></RowDefinition>            
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="80"></RowDefinition>
        </Grid.RowDefinitions>
 
        <Image Grid.Row="0" Height="80" HorizontalAlignment="Left" Source="logo.jpg" Name="test" Stretch="Fill" VerticalAlignment="Top" Width="1200" />
        <sdk:DataGrid 
               Name="dataGrid1" Height="400"  Width="1200" HorizontalAlignment="Left" Grid.Row="1"
               AutoGenerateColumns="False"    Background="Bisque" 
               GridLinesVisibility="Vertical" HeadersVisibility="All" 
               RowBackground="LightYellow"    AlternatingRowBackground="LightBlue"
               BorderBrush="Gray"             BorderThickness="5"      
               ColumnWidth="100"              RowHeight="40" GotFocus="dataGrid1_GotFocus" 
               SelectionChanged="dataGrid1_SelectionChanged">   
 
            <sdk:DataGrid.Columns>                
                <sdk:DataGridTextColumn Binding="{Binding civilite}"           x:Name="colonneCivilite" Header="Civilité" />    
                <sdk:DataGridTextColumn Binding="{Binding nom}"                x:Name="colonneNom"      Header="Nom" />
                <sdk:DataGridTextColumn Binding="{Binding prenom}"             x:Name="colonnePrenom"   Header="Prénom"  />
                <sdk:DataGridTextColumn Binding="{Binding diplome}"            x:Name="diplome"         Header="Diplôme"/>
                <sdk:DataGridTextColumn Binding="{Binding mention}"            x:Name="colonneMention"  Header="Mention"/>
                <sdk:DataGridTextColumn Binding="{Binding annee_universitaire}"                         Header="Année"/>
                <sdk:DataGridTextColumn Binding="{Binding ufr}"                                         Header="U.F.R." x:Name="colonneUFR"/>
                <sdk:DataGridTextColumn Binding="{Binding lieu_naissance}"  Header="né(e) à" x:Name="colonneLieuNaissance"/>
                <sdk:DataGridTextColumn Binding="{Binding j_naissance}"     Header="jour"    x:Name="colonneJourNaissance" />
                <sdk:DataGridTextColumn Binding="{Binding m_naissance}"     Header="mois"    x:Name="colonneMoisNaissance" />
                <sdk:DataGridTextColumn Binding="{Binding a_naissance}"     Header="année"   x:Name="colonneAnNaissance" />
                <sdk:DataGridTextColumn Binding="{Binding date_arrete}"     Header="Date arrêté"        x:Name="colonneArrete" />
                <sdk:DataGridTextColumn Binding="{Binding num_diplome_saisi}"     Header="N° Diplôme"   x:Name="colonneNumDiplome" />
                <sdk:DataGridTextColumn Binding="{Binding num_diplome}" Header="N° Diplome" x:Name="colonneNumDiplomeE" />
 
            </sdk:DataGrid.Columns>     
 
        </sdk:DataGrid>
        <Button Content="Créér un diplôme" Grid.Row="2" Height="23" HorizontalAlignment="Left" Margin="12,19,0,0" Name="button1" VerticalAlignment="Top" Width="170" Click="boutonCreationDiplome" />
        <Button Content="Aide" Grid.Row="2" Height="23" HorizontalAlignment="Left" Margin="202,19,0,0" Name="button2" VerticalAlignment="Top" Width="170" />
        <Button Content="Valider pour modifier" Grid.Row="2" Height="23" HorizontalAlignment="Left" Margin="12,45,0,0" Name="button3" VerticalAlignment="Top" Width="170" Click="boutonModificationDiplome" />
    </Grid>
le problème c'est qu'à l'affichage, j'aimerais que la largeur de mes colonnes s'adaptent au contenu le plus grand pour chaque colonne.
J'ai essayé quelques trucs qui n'ont pas fonctionné.
Merci de m'aider.