wpf columnwidth设为auto 其中的gridview列宽会有问题

本人wpf小菜鸟 而且刚注册论坛没有币 还望各位大神帮帮忙

如图 三列的每一列我都想width =auto，但是gridview的列宽就变成这样了。问题出在哪里呢？应该怎么处理

 <Grid Name="MainGrid">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="Auto"/>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="100"/>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="Auto"/>
            </Grid.RowDefinitions>

        <StackPanel Grid.Row="0" Grid.Column="0">
            <TextBox HorizontalAlignment="Left" VerticalAlignment="Center" HorizontalContentAlignment="Right"  Width="200" Margin="10"/>
        </StackPanel>

        <DataGrid x:Name="DgvShow" AutoGenerateColumns="False"  CanUserSortColumns="False" IsReadOnly="True" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="3" >
            <DataGrid.Resources>
                <my:OriginConverter x:Key="orginConverter"/>
            </DataGrid.Resources>
            <DataGrid.Columns>
                <DataGridTextColumn Width="1*" Header="产地" Binding="{Binding origin, Converter={StaticResource orginConverter}}"></DataGridTextColumn>
                <DataGridTextColumn Width="1*" Header="名称" Binding="{Binding productname}"></DataGridTextColumn>
                <DataGridTextColumn Width="1*" Header="规格" Binding="{Binding dimensions}"></DataGridTextColumn>
                <DataGridTextColumn Width="1*" Header="色码" Binding="{Binding colorcode}"></DataGridTextColumn>
            </DataGrid.Columns>
        </DataGrid>

        <StackPanel Grid.Row="2" Grid.Column="1">
            <TextBox HorizontalAlignment="Left" VerticalAlignment="Center" Width="100" Margin="10"/>
        </StackPanel>

            <StackPanel Grid.Row="3" Grid.Column="2">
                <TextBox HorizontalAlignment="Left" VerticalAlignment="Center" Width="100" Margin="10"/>
            </StackPanel>
        </Grid>

是你DataGrid的相关属性没有设置对，
你再试把datagrid放在一个新grid里面试试，看看会不会出现这种情况