Xamarin.Forms、XAML、绑定和 isVisible [英] Xamarin.Forms, XAML, Bindings and isVisible

问题描述

我(显然，关于这个问题)对此很陌生，所以在此先感谢您的帮助！由于我现在在这方面努力了几个小时，我希望有人可以加快我的学习曲线 :)

I am (obviously, regarding the question) new to this, so thanks in advance for any help! As I am trying my current best on this for hours now, I hope, someone can accelerate my learning curve :)

附录:我也在 Xamarin 论坛上发帖，但是关于问题的答案数量，这似乎已经死了.所以我希望没有人冒犯.

Addendum: I also posted on the Xamarin Forum, however this seems to be rather dead regarding the amount of answers to questions. Therefore I hope no one takes offense.

所以，我有我的 XAML MainPage:

So, I have my XAML MainPage:

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="cant post links"
             xmlns:x="cant post links"
             xmlns:local="clr-namespace:App.ViewModels"
             x:Class="App.ViewModels.MainPage">

    <ContentPage.BindingContext>
        <local:User/>
    </ContentPage.BindingContext>

    <StackLayout>
        <Label Text="Test"/>
        <ListView ItemsSource="{Binding Changes}"
                  x:Name="ChangesList"
                  HasUnevenRows="True"
                  Margin="40,80"
                  ItemTapped="ListView_ItemTapped">
            <ListView.ItemTemplate>
                <DataTemplate>
                    <ViewCell>
                        <StackLayout>
                            <Label Text="{Binding Name}"/>
                            <Button Text="Details"
                                    IsVisible="{Binding IsVisible}"/>
                        </StackLayout>
                    </ViewCell>
                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>
        <Button Text="Press to add" x:Name="addItem" Clicked="addItem_Clicked"/>
    </StackLayout>

</ContentPage>

我有一个带有相应属性的数据模型.当我离开 MainPage 类构造函数时，如下所示:

I have a datamodel with the correponding attributes behind. When I leave the MainPage class constructor like the following:

public MainPage()
{
    InitializeComponent();
}

我看不到任何列表项.

那么，第一个问题:我想，基于绑定，应用程序会自动生成一个 User 实例并将其分配到列表中?

正如我在调试器中看到的那样，实际上生成了一个 User 实例并将其分配给了 BindingContext，但 ChangesList.ItemsSource 仍然为空.

As I can see with the debugger, a User instance actually is generated and also assigned to the BindingContext, but the ChangesList.ItemsSource remains null.

因此，我更改了构造函数的代码:

Therefore, I changed the code of the constructor:

public MainPage()
{
    InitializeComponent();
    var bc = BindingContext;
    var list = ChangesList.ItemsSource;
    ChangesList.ItemsSource = (bc as User).Changes;
}

这让我可以在编译和运行应用程序时看到一个包含项目的列表.此外，我可以通过addItem"按钮后面的代码将新项目添加到列表中.但是:当我点击一个项目时，没有任何反应.代码如下所示:

This lets me see a list with items when I compile and run the app. Also, I can add new items to the list via the code behind the 'addItem' Button. However: Nothing happens, when I tap an item. The code looks like follows:

private void ListView_ItemTapped(object sender, ItemTappedEventArgs e)
{
    var change = e.Item as Change;
    change.IsVisible = !change.IsVisible;
}

Data 方法如下所示:

and the Data methods look as follows:

 public class Change : INotifyPropertyChanged
{
    public string Name { get; set; }
    bool isVisible = false;

    public event PropertyChangedEventHandler PropertyChanged;

    public bool IsVisible
    {
        get
        {
            return isVisible;
        }
        set
        {
            isVisible = value;
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Change-IsVisible"));
        }
    }
}

因此第二个问题:为什么 Button 不改变其可见性状态并变为可见?

在此先非常感谢您！

狼

添加了完整的更改"类代码.

Added the complete "Change" Class Code.

编辑 2:用户代码.

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Text;
using System.ComponentModel;
using Xamarin.Forms;
using System.Diagnostics;

namespace App.ViewModels
{
    public class User : INotifyPropertyChanged
    {
        public string Username { get; set; }
        public ObservableCollection<Change> Changes = null;   
        public event PropertyChangedEventHandler PropertyChanged;

        public User()
        {
            Changes = new ObservableCollection<Change>();
            addChange("Test 1");
            addChange("Test 2");

        }

        public void addChange(string text)
        {
            Change c = new Change
            {
                Name = text,
                IsVisible = false
            };
            Changes.Add(c);
            refresh();
        }

        public void refresh()
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Changes"));
        }
    }
}

推荐答案

对于第二个问题 - 尝试:

For the 2nd question - try:

PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("IsVisible"));

对于第一个问题 - 您能否分享您的用户源代码

For the first question - can you please share your User source code

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