无法从 Xamarin 中的列表视图上的 JSON 输出信息

Question

我一直在尝试用MVVM学习Xamarin，我仍然在努力。我遇到的问题主要是试图在ListView中从JSON文件输出信息。
如果我忽略MVVM并直接将代码添加到视图中，它就可以完美地工作。然而，当我尝试在ViewModel中使用代码时，它找不到绑定的Itemssource。
代码:
ListPageVM

using SaveUp.Model;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.IO;
using SaveUp.View;
using System.Reflection;
using System.Text;
using System.ComponentModel;
using System.Runtime.CompilerServices;
namespace SaveUp.ViewModel
{
public class ListPageVM : INotifyPropertyChanged
{
private ObservableCollection<MainModel> data;
public ListPageVM()
{
var assembly = typeof(ListPageVM).GetTypeInfo().Assembly;
Stream stream = assembly.GetManifestResourceStream("SaveUp.eintraege.json");
using (var reader = new StreamReader(stream))
{
var json = reader.ReadToEnd();
List<MainModel> dataList = JsonConvert.DeserializeObject<List<MainModel>>(json);
data = new ObservableCollection<MainModel>(dataList);
lw.ItemsSource = data;
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
}

ListPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="SaveUp.View.ListPage"
xmlns:viewModel="clr-namespace:SaveUp.ViewModel"
x:DataType="viewModel:ListPageVM">
<ContentPage.BindingContext>
<viewModel:ListPageVM/>
</ContentPage.BindingContext>
<ContentPage.Content>
<StackLayout>
<ListView x:Name="lw"
Footer="">
<ListView.ItemTemplate>
<DataTemplate>
<TextCell Text="{Binding Geld}" Detail="{Binding Detail}"/>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
</ContentPage.Content>
</ContentPage>

eintraege.json

[
{
"Geld": 500.00,
"Detail": "Kaffee"
},
{
"Geld": 250.00,
"Detail": "Creme"
},
{
"Geld": 100.00,
"Detail": "Yogurt"
}
]

Answer 1

首先，它需要有一个公共属性

private ObservableCollection<MainModel> data;

应该看起来像

private ObservableCollection<MainModel> data;
public ObservableCollection<MainModel> Data { 
get
{
return data;
{
set
{
data = value;
OnPropertyChanged();
}
}

如果你正在使用MVVM，那么你的VM不会直接与你的视图交互

// get rid of this
lw.ItemsSource = data;

然后在XAML中使用binding来设置ItemsSource

<ListView ItemsSource="{Binding Data}" ...