ContentPresenter 未显示 ControlTemplate Xamarin Forms 内的内容

Question

I want to create a reusable template page that I want to use throughout my app.

I decided to go with a ControlTemplate to achieve this but I am having issues. The first issue is that the HeaderText does not get displayed when I bind to it. The second issue is that the Page using this ControlTemplate does not have his children visible, the ContentPresenter is empty.

ControlTemplate:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         x:Class="Project.MainViewTemplate">
<ContentPage.ControlTemplate>
    <ControlTemplate>
        <Grid RowSpacing="0">
            <Grid.RowDefinitions>
                <RowDefinition Height="2*"/>
                <RowDefinition Height="*"/>
            </Grid.RowDefinitions>

            <Label TextColor="Black"
                   Text="{TemplateBinding HeaderText}"
                   BackgroundColor = "Green"
                   Grid.Row="0"/>

            <ContentPresenter Grid.Row="1"/>
        </Grid>
    </ControlTemplate>
</ContentPage.ControlTemplate>

And its code behind:

public partial class MainViewTemplate : ContentPage
{
    public static readonly BindableProperty HeaderTextProperty = BindableProperty.Create(nameof(HeaderText), typeof(string), typeof(MainViewTemplate), default(string));

    public string HeaderText
    {
        get { return (string)GetValue(HeaderTextProperty); }
        set { SetValue(HeaderTextProperty, value); }
    }

    public MainViewTemplate()
    {
        InitializeComponent();
    }
}

Page that uses it:

<template:MainViewTemplate xmlns="http://xamarin.com/schemas/2014/forms"
                       xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
                       x:Class="Project.MainView"
                       xmlns:template="clr-namespace:Project"
                       HeaderText="Main view">
     <StackLayout Margin="10"
                  BackgroundColor="Green">
         <Label Text = "Test"/>
     </StackLayout>
</template:MainViewTemplate>

The label that binds HeaderText is not showing its text, if i change it to write hardcoded text it works, so something is off with the binding. Secondly, I can see the green background as well. Secondly, the contentpresenter is not showing the content inside the page that uses this ControlTemplate.

Answer 1

I don't see you use Template in your code correctly, I do one sample that you can take a look:

ControlTemplate, there one control x:key="template1"

<ContentPage
x:Class="demo3.template.MainViewTemplate"
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml">
<ContentPage.Resources>
    <ControlTemplate x:Key="template1">
        <Grid RowSpacing="0">
            <Grid.RowDefinitions>
                <RowDefinition Height="2*" />
                <RowDefinition Height="*" />
            </Grid.RowDefinitions>

            <Label
                Grid.Row="0"
                BackgroundColor="Green"
                Text="{TemplateBinding HeaderText}"
                TextColor="Black" />

            <ContentPresenter Grid.Row="1" />
        </Grid>
    </ControlTemplate>
</ContentPage.Resources>

public partial class MainViewTemplate : ContentPage
{
    public static readonly BindableProperty HeaderTextProperty = BindableProperty.Create(nameof(HeaderText), typeof(string), typeof(MainViewTemplate), default(string));

    public string HeaderText
    {
        get => (string)GetValue(HeaderTextProperty);
        set => SetValue(HeaderTextProperty, value);
    }

    public MainViewTemplate()
    {
        InitializeComponent();
    }
}

Using ControlTemplate x:key=""template

<control:MainViewTemplate
x:Class="demo3.template.Page1"
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:control="clr-namespace:demo3.template"
ControlTemplate="{StaticResource template1}"
HeaderText="Main view">
<ContentPage.Content>
    <StackLayout Margin="10" BackgroundColor="Green">
        <Label Text="Test" />
    </StackLayout>
</ContentPage.Content>
  </control:MainViewTemplate>

The screenshot:

More detailed info about ControlTemplate, please take a look:

https://docs.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/templates/control-template#substitute-content-into-a-contentpresenter