Xamarin.Forms中的我的未显示？

当我在主页中添加工具栏时，内容页将消失。我该怎么做才能解决这个问题？你能和我分享你的见解或给我指点链接让我学习吗。我只是从xamarin表单开始。我一整天都在寻找答案，但找不到答案

<?xml version="1.0" encoding="utf-8" ?>
    <ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
                 xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
                 xmlns:local="clr-namespace:KLConnect"
                 x:Class="KLConnect.MainPage"
                 Title="KLConnect TTM+ Operation">

        <Label x:Name="label"
               FontSize="Medium"
               VerticalOptions="Center" 
               HorizontalOptions="Center" />

        <ContentPage.ToolbarItems>

            <ToolbarItem Text="setting"
                         Order="Primary"
                         Clicked="OnToolbarItemClicked">
                <ToolbarItem.Icon>
                    <OnPlatform x:TypeArguments="FileImageSource"
                                Android="ic_build_white_48dp.png"/>
                </ToolbarItem.Icon>
            </ToolbarItem>

            <ToolbarItem Text="close"
                         Order="Primary"
                         Clicked="OnToolbarItemClicked">
                <ToolbarItem.Icon>
                    <OnPlatform x:TypeArguments="FileImageSource"
                                Android="ic_highlight_off_white_48dp.png"/>
                </ToolbarItem.Icon>
            </ToolbarItem>

            <ToolbarItem Text="help"
                         Order="Primary"
                         Clicked="OnToolbarItemClicked">
                <ToolbarItem.Icon>
                    <OnPlatform x:TypeArguments="FileImageSource"
                                Android="ic_help_outline_white_48dp.png"/>
                </ToolbarItem.Icon>
            </ToolbarItem>

        </ContentPage.ToolbarItems>

        <ContentPage.Resources>
            <ResourceDictionary>
                <Style x:Key="plainButton" TargetType="Button">
                    <Setter Property="BackgroundColor" Value="#eee"/>
                    <Setter Property="TextColor" Value="Black" />
                    <Setter Property="BorderRadius" Value="0"/>
                    <Setter Property="FontSize" Value="40" />
                </Style>
                <Style x:Key="darkerButton" TargetType="Button">
                    <Setter Property="BackgroundColor" Value="#ddd"/>
                    <Setter Property="TextColor" Value="Black" />
                    <Setter Property="BorderRadius" Value="0"/>
                    <Setter Property="FontSize" Value="40" />
                </Style>
                <Style x:Key="orangeButton" TargetType="Button">
                    <Setter Property="BackgroundColor" Value="#E8AD00"/>
                    <Setter Property="TextColor" Value="White" />
                    <Setter Property="BorderRadius" Value="0"/>
                    <Setter Property="FontSize" Value="40" />
                </Style>
            </ResourceDictionary>
        </ContentPage.Resources>

        <ContentPage.Content>
            <Grid x:Name="controlGrid" RowSpacing="1" ColumnSpacing="1">
                <Grid.RowDefinitions>
                    <RowDefinition Height="150" />
                    <RowDefinition Height="*" />
                    <RowDefinition Height="*" />
                    <RowDefinition Height="*" />
                    <RowDefinition Height="*" />
                    <RowDefinition Height="*" />
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="*" />
                    <ColumnDefinition Width="*" />
                    <ColumnDefinition Width="*" />
                    <ColumnDefinition Width="*" />
                </Grid.ColumnDefinitions>
                <Label Text="0" Grid.Row="0" HorizontalTextAlignment="End" VerticalTextAlignment="End" TextColor="White"
            FontSize="60" Grid.ColumnSpan="4" />
                <Button Text = "C" Grid.Row="1" Grid.Column="0"
            Style="{StaticResource darkerButton}" />
                <Button Text = "+/-" Grid.Row="1" Grid.Column="1"
            Style="{StaticResource darkerButton}" />
                <Button Text = "%" Grid.Row="1" Grid.Column="2"
            Style="{StaticResource darkerButton}" />
                <Button Text = "div" Grid.Row="1" Grid.Column="3"
            Style="{StaticResource orangeButton}" />
                <Button Text = "7" Grid.Row="2" Grid.Column="0"
            Style="{StaticResource plainButton}" />
                <Button Text = "8" Grid.Row="2" Grid.Column="1"
            Style="{StaticResource plainButton}" />
                <Button Text = "9" Grid.Row="2" Grid.Column="2"
            Style="{StaticResource plainButton}" />
                <Button Text = "X" Grid.Row="2" Grid.Column="3"
            Style="{StaticResource orangeButton}" />
                <Button Text = "4" Grid.Row="3" Grid.Column="0"
            Style="{StaticResource plainButton}" />
                <Button Text = "5" Grid.Row="3" Grid.Column="1"
            Style="{StaticResource plainButton}" />
                <Button Text = "6" Grid.Row="3" Grid.Column="2"
            Style="{StaticResource plainButton}" />
                <Button Text = "-" Grid.Row="3" Grid.Column="3"
            Style="{StaticResource orangeButton}" />
                <Button Text = "1" Grid.Row="4" Grid.Column="0"
            Style="{StaticResource plainButton}" />
                <Button Text = "2" Grid.Row="4" Grid.Column="1"
            Style="{StaticResource plainButton}" />
                <Button Text = "3" Grid.Row="4" Grid.Column="2"
            Style="{StaticResource plainButton}" />
                <Button Text = "+" Grid.Row="4" Grid.Column="3"
            Style="{StaticResource orangeButton}" />
                <Button Text = "0" Grid.ColumnSpan="2"
            Grid.Row="5" Grid.Column="0" Style="{StaticResource plainButton}" />
                <Button Text = "." Grid.Row="5" Grid.Column="2"
            Style="{StaticResource plainButton}" />
                <Button Text = "=" Grid.Row="5" Grid.Column="3"
            Style="{StaticResource orangeButton}" />
            </Grid>
        </ContentPage.Content>

    </ContentPage>

这是因为在xaml的开头已经设置了标签

去掉这个

<Label x:Name="label"
       FontSize="Medium"
       VerticalOptions="Center" 
       HorizontalOptions="Center" />

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我知道。它发生了；