在TabItem/StackPanel中自动调整WPF框架对象的大小

我希望框架控件自动调整大小以填充选项卡项内的屏幕。是下面的代码，它呈现一个非常小的帧。我宁愿不设置静态高度和宽度。这是XAML

<TabItem Header="Reports" Name="tReports" Height="50" BorderBrush="Transparent" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="100">
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition />
                    <RowDefinition />
                </Grid.RowDefinitions>
                <ComboBox Grid.Row="0" Name="cmbReport" Width="200" HorizontalAlignment="Left" />
                <Frame Grid.Row="1" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" Source="http://online/home/" Margin="0,15,0,0" />
            </Grid>
            </TabItem>

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这是可行的，关键部分不是设置第二行definition Height=“Auto”，而是需要设置第一行，否则框架只占屏幕的1/2左右，如图所示

            <TabItem Header="Reports" Name="tReports" Height="50" BorderBrush="Transparent" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="100">
                <Grid>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="Auto" />
                        <RowDefinition />
                    </Grid.RowDefinitions>
                    <ComboBox Grid.Row="0" Name="cmbReport" Width="200" HorizontalAlignment="Left">
                    </ComboBox>
                    <Frame Grid.Row="1" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" Source="http://online/home/" Margin="0,15,0,0" />
                </Grid>
            </TabItem>

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谢谢，这很有帮助。我还需要提到的是，我必须在TabItem控件中添加另一个控件。一旦我创建了另一个控件，框架就不会垂直填充。有关更新XAML，请参阅我的原始问题。

            <TabItem Header="Reports" Name="tReports" Height="50" BorderBrush="Transparent" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="100">
                <Grid>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="Auto" />
                        <RowDefinition />
                    </Grid.RowDefinitions>
                    <ComboBox Grid.Row="0" Name="cmbReport" Width="200" HorizontalAlignment="Left">
                    </ComboBox>
                    <Frame Grid.Row="1" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" Source="http://online/home/" Margin="0,15,0,0" />
                </Grid>
            </TabItem>