XAML - 属性"内容"设置不止一次

Question

对WPF和XAML来说很新.我无法理解为什么我不能在下面的代码中将WPF控件放在我想要的位置.我的问题是<canvas></canvas>标签的位置.我放在这个地方的任何东西都给了我'属性'内容'设置不止一次'

如果有人能用简单的术语解释内容属性设置哪个最有帮助.

我查看了以下文章无济于事: 属性'内容'被多次 设置属性内容被设置多次 属性内容被设置多次 属性'内容'被设置多次按钮WPF ControlTemplate导致错误"属性'内容'设置不止一次"

<Window x:Class="PDFIndexer.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<Grid x:Name="ParentGrid">
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="1*" />
        <RowDefinition Height="25" />
    </Grid.RowDefinitions>
    <Menu Grid.Row="0" >
        <MenuItem Header="File" >
            <MenuItem Header="Open Project" Click="MenuItem_Click_1"></MenuItem>
            <MenuItem Header="Save Project"></MenuItem>
            <MenuItem Header="Close Project"></MenuItem>
            <Separator></Separator>
            <MenuItem Header="Exit"></MenuItem>
        </MenuItem>
        <MenuItem Header="Edit"></MenuItem>
    </Menu>
    <TabControl Grid.Row="1">
        <TabItem Header="Document Flow" >
            This is where the outline of the entire document will be placed.
            <Canvas></Canvas>
         </TabItem>
        <TabItem Header="Preview">
            This is where the preview will be drawn to screen.
        </TabItem>
        <TabItem Header="Resources">
            This is where the resources { graphic files, fonts, data files }
        </TabItem>
        <TabItem Header="Code Library">
            This is where the user can save re-usable bits of code. Useful when adding intel barcodes or Address blocks etc...
        </TabItem>
    </TabControl>


    <StatusBar Grid.Row="2">
        Items
    </StatusBar>
</Grid>

Answer 1

通过向您TabItem添加的内容添加文本描述,然后在添加Canvas时添加了一个不允许的内容的其他内容项TabItem.你需要使用一个可以容纳一组孩子的控件,比如Canvas,Grid,StackPanel等.尝试这样的事情.

<TabControl Grid.Row="1">
    <TabItem Header="Document Flow">
        <Canvas>
            <TextBlock>
                This is where the outline of the entire document will be placed.
            </TextBlock>
        </Canvas>
    </TabItem>
    <TabItem Header="Preview">
        This is where the preview will be drawn to screen.
    </TabItem>
    <TabItem Header="Resources">
        This is where the resources { graphic files, fonts, data files }
    </TabItem>
    <TabItem Header="Code Library">
        This is where the user can save re-usable bits of code. Useful when adding intel barcodes or Address blocks etc...
    </TabItem>
</TabControl>

Answer 2

某些容器只允许1个元素,其他容器允许> 1个元素.当您收到错误消息"内容"被设置多次时,这意味着您已尝试将多种类型的元素放在仅允许1个元素的容器中.

也许尝试这个(未测试):

<TabItem Header="Document Flow" >
<StackPanel>
<TextBlock>This is where the outline of the entire document will be placed. </TextBlock>
<Canvas></Canvas>
</StackPanel>
</TabItem>