C# WPF MVVM下显示ObservableCollection集合Count Add或者Remove界面不更新的解决方法-TCPGAME

现在有个需求，就是要在TextBlock控件上显示ObservableCollection的count，但是发现绑定后出现ObservableCollection数量变化时，TextBlock的内容却不刷新的问题。

ObservableCollection表示一个动态数据集合，它可在添加、删除项目或刷新整个列表时提供通知。
[microsoft官方文档](https://docs.microsoft.com/zh-cn/dotnet/api/system.collections.objectmodel.observablecollection-1?view=netframework-4.5&f1url=%3FappId%3DDev16IDEF1%26l%3DZH-CN%26k%3Dk%28System.Collections.ObjectModel.ObservableCollection%601%29;k%28TargetFrameworkMoniker-.NETFramework,Version%253Dv4.5%29;k%28DevLang-csharp%29%26rd%3Dtrue "microsoft官方文档")

常规的绑定方式是，首先在ViewModel中定义集合
```
 public class VMMain: BaseNotify
 {
	private ObservableCollection<int> numbers;
	public ObservableCollection<int> Numbers
	{
		get => numbers;
		set => SetProperty(ref numbers, value);
	}
	
	public VMMain()
	{
		Numbers = new ObservableCollection<int>(new List<int> {1,2,3,4,5,6,7,8,9 });
	}
}
```
其中**BaseNotify基类**请到文章后面查看**BaseNotify.cs**

在界面中这样绑定显示
```
 <TextBlock 
	 HorizontalAlignment="Center"
	 VerticalAlignment="Center"
	 FontSize="32"
	 Text="{Binding Numbers,Converter={StaticResource ObservableCollectionCountConverter}}"/>
```

其中ObservableCollectionCountConverter转换器的代码请到文章后面查看**ObservableCollectionCountConverter.cs**

程序界面运行起来后，首次显示的数量为9，是正确的，但是之后对ObservableCollection集合进行元素的add或者remove操作，实际上界面并不会刷新，还保留着之前的显示的9，这并不是我们想实现的效果。实际上是ObservableCollection实现接口的数据集合的内置实现 INotifyCollectionChanged ，所以他元素变化是通知了INotifyCollectionChanged事件。普通非列表控件的绑定，实际上只监听INotifyPropertyChanged的变化，所以add或者remove以及clear不会影响普通绑定。

###解决方案
在ObservableCollection的CollectionChanged中通知界面更新，仅需修改ViewModel即可，修改后的VMMain如下：
```
public class VMMain : BaseNotify
{
	private ObservableCollection<int> numbers;
	public ObservableCollection<int> Numbers
	{
		get => numbers;
		set => SetProperty(ref numbers, value);
	}

public VMMain()
	{
		Numbers = new ObservableCollection<int>(new List<int> {1,2,3,4,5,6,7,8,9 });
		Numbers.CollectionChanged += Numbers_CollectionChanged;
	}

private void Numbers_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
	{
		RaisePropertyChanged("Numbers");
	}
}
```
问题解决！

###完整代码
####VMMain.cs
```
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Threading;

namespace TcpGameDemo
{
	public class VMMain : BaseNotify
	{
		private ObservableCollection<int> numbers;
		public ObservableCollection<int> Numbers
		{
			get => numbers;
			set => SetProperty(ref numbers, value);
		}

public VMMain()
		{
			Numbers = new ObservableCollection<int>(new List<int> {1,2,3,4,5,6,7,8,9 });
            Numbers.CollectionChanged += Numbers_CollectionChanged;

DispatcherTimer dispatcher = new DispatcherTimer();
            dispatcher.Tick += Dispatcher_Tick;
			dispatcher.Interval = TimeSpan.FromMilliseconds(1000);
			dispatcher.Start();
		}

private void Dispatcher_Tick(object sender, EventArgs e)
        {
			Numbers.Add(999);
		}

private void Numbers_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
        {
			RaisePropertyChanged("Numbers");
        }
    }
}

```
####BaseNotify.cs
```
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;

namespace BatteryPackInfo
{
	public class TcpGameDemo : INotifyPropertyChanged
	{
		public event PropertyChangedEventHandler PropertyChanged;

/// <summary>
		/// 属性发生改变时调用该方法发出通知
		/// </summary>
		/// <param name="propertyName">属性名称</param>
		public void RaisePropertyChanged(string propertyName)
		{
			if (PropertyChanged != null)
			{
				PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
			}
		}

protected bool SetProperty<T>(ref T target, T value, [CallerMemberName] string propertyName = null)
		{
			if (EqualityComparer<T>.Default.Equals(target, value))
			{
				return false;
			}

target = value;
			RaisePropertyChanged(propertyName);
			return true;
		}
	}
}

```
####MainWindow.xaml
```
<Window x:Class="TcpGameDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:TcpGameDemo" xmlns:converters="clr-namespace:TcpGameDemo.Converters"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Window.DataContext>
        <local:VMMain></local:VMMain>
    </Window.DataContext>
    <Window.Resources>
        <converters:ObservableCollectionCountConverter x:Key="ObservableCollectionCountConverter"></converters:ObservableCollectionCountConverter>
    </Window.Resources>
    <Grid>
        <TextBlock 
            HorizontalAlignment="Center"
            VerticalAlignment="Center"
            FontSize="32" 
            Text="{Binding Numbers,Converter={StaticResource ObservableCollectionCountConverter}}"/>
    </Grid>
</Window>

```
####ObservableCollectionCountConverter.cs
```
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Data;

namespace TcpGameDemo.Converters
{
    public class ObservableCollectionCountConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
           var collection = value as ObservableCollection<int>;
            if (collection == null)
                return 0;
            else
                return collection.Count();
        }

public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}
```