MVVM更容易内存泄露吗？

由于MVVM是把View, ViewModel, Model紧紧绑定在一起的模式，特别视图和视图模型通过实现观察者模式双向绑定和NotifyPropertyChanged事件，似乎更加容易造成内存泄露/内存不释放。网上也有这种说法。真的是这样的吗？我们来实际测试一下。

实际测试MVVM是不是容易内存泄露

为了说明问题，我把MVVM搞复杂一点，在ViewModel里面引用一个Singleton单例模式的Service，这个Service定义如下：

namespace SilverlightApplication1.Service
{
    public class GlobalService
    {
        private static readonly GlobalService Instance = new GlobalService();

        static GlobalService()
        {
        }

        public static GlobalService GetInstance()
        {
            return Instance;
        }
    }
}

写一个ViewModel，里面引用了Service，用到了ICommand，实现了INotifyPorpertyChanged接口：

using System.ComponentModel;
using System.Windows.Input;
using SilverlightApplication1.Service;

namespace SilverlightApplication1.MVVM
{
    public class ViewModel1 : INotifyPropertyChanged
    {
        private GlobalService _injectSingletonService;

        public ViewModel1(GlobalService injectSingletonService)
        {
            Property1 = "test1";
            Command1 = new DelegateCommand(LoadMe, CanLoadMe);

            _injectSingletonService = injectSingletonService;
        }

        private string _property1;
        public string Property1
        {
            get { return _property1; }
            set
            {
                _property1 = value;

                if (PropertyChanged != null)
                {
                    PropertyChanged(this,
                        new PropertyChangedEventArgs("Property1"));
                }
            }
        }

        public ICommand Command1 { get; set; }
        public event PropertyChangedEventHandler PropertyChanged;

        private void LoadMe(object param)
        {

        }

        private bool CanLoadMe(object param)
        {
            return true;
        }
    }
}

来一个视图View，绑定ViewModel，有个button绑定了ICommand，属性也绑定了。

<UserControl x:Class="SilverlightApplication1.MVVM.View1"
    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"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">

    <Grid x:Name="LayoutRoot" Background="White">
        <TextBlock Height="65" HorizontalAlignment="Left" Margin="57,82,0,0" Name="textBlock1" Text="this is view1" VerticalAlignment="Top" Width="224" FontSize="18" />
        <Button Content="Button" Command="{Binding Command1}" Height="28" HorizontalAlignment="Left" Margin="55,130,0,0" Name="button1" VerticalAlignment="Top" Width="111" />
        <TextBlock Height="28" HorizontalAlignment="Left" Margin="56,173,0,0" Name="textBlock2" Text="{Binding Property1}" VerticalAlignment="Top" Width="114" />
    </Grid>
</UserControl>

这个View1的界面是这样子的：

View1.xaml.cs代码：

using System.Windows.Controls;
using SilverlightApplication1.Service;

namespace SilverlightApplication1.MVVM
{
    public partial class View1 : UserControl
    {
        public View1()
        {
            InitializeComponent();

            this.DataContext = new ViewModel1(GlobalService.GetInstance());
        }
    }
}

辅助类DelegateCommand源码：

using System;
using System.Windows.Input;

namespace SilverlightApplication1
{
    public class DelegateCommand : ICommand
    {
        public event EventHandler CanExecuteChanged;

        Func<object, bool> canExecute;
        Action<object> executeAction;
        bool canExecuteCache;

        public DelegateCommand(Action<object> executeAction,
        Func<object, bool> canExecute)
        {
            this.executeAction = executeAction;
            this.canExecute = canExecute;
        }

        #region ICommand Members

        /// <summary>

        /// Defines the method that determines whether the command

        /// can execute in its current state.

        /// </summary>

        /// <param name="parameter">

        /// Data used by the command.

        /// If the command does not require data to be passed,

        /// this object can be set to null.

        /// </param>

        /// <returns>

        /// true if this command can be executed; otherwise, false.

        /// </returns>

        public bool CanExecute(object parameter)
        {

            bool tempCanExecute = canExecute(parameter);



            if (canExecuteCache != tempCanExecute)
            {

                canExecuteCache = tempCanExecute;

                if (CanExecuteChanged != null)
                {

                    CanExecuteChanged(this, new EventArgs());

                }

            }



            return canExecuteCache;

        }



        /// <summary>

        /// Defines the method to be called when the command is invoked.

        /// </summary>

        /// <param name="parameter">

        /// Data used by the command.

        /// If the command does not require data to be passed,

        /// this object can be set to null.

        /// </param>

        public void Execute(object parameter)
        {

            executeAction(parameter);

        }

        #endregion
    }
}

MainPage的代码：

<UserControl x:Class="SilverlightApplication1.MainPage"
    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"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400" xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk">

    <Grid x:Name="LayoutRoot" Background="White">
        <Button Content="Add view" Height="36" HorizontalAlignment="Left" Margin="20,31,0,0" Name="button1" VerticalAlignment="Top" Width="115" Click="button1_Click" />
        <sdk:TabControl Height="197" HorizontalAlignment="Left" Margin="28,82,0,0" Name="tabControl1" VerticalAlignment="Top" Width="346">
            <sdk:TabItem Header="tabItem1" Name="tabItem1">
                <Grid />
            </sdk:TabItem>
        </sdk:TabControl>
        <Button Content="Close view" Height="35" HorizontalAlignment="Left" Margin="148,32,0,0" Name="button2" VerticalAlignment="Top" Width="108" Click="button2_Click" />
    </Grid>
</UserControl>

MainPage界面，主要是在Tab里面打开View1，不断打开关闭，打开关闭，因为View1是用MVVM模式实现的，看看有内存泄露：

MainPage.xaml.cs，就是测试代码，正常情况下点击关闭tab，可能GC不会立即回收内存，这里为了便于测试，手动加了GC.Collect。（正常情况下，不推荐使用GC.Collect()）

using System;
using System.Windows;
using System.Windows.Controls;
using SilverlightApplication1.MVVM;

namespace SilverlightApplication1
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            var v = new View1();
            TabItem t = new TabItem {Content = v, Header = "header " + DateTime.Now.Second.ToString()};
            this.tabControl1.Items.Add(t);
        }

        private void button2_Click(object sender, RoutedEventArgs e)
        {
            this.tabControl1.Items.RemoveAt(0);//view1, viewModel1并没有立即释放，由GC决定何时决定。

            System.GC.Collect();
            System.GC.WaitForPendingFinalizers();

            //{
            //    FooContext context = new FooContext();
            //    context.Load(context.MyQuery);
            //}
        }
    }
}

 

测试结果：内存泄露和MVVM无关

我的测试结果是内存能够释放，没有内存泄露问题，也就是说MVVM模式和内存泄露无关。那种所谓的MVVM更容易内存泄露的说法没有什么道理。但不排除你的ViewModel和Model里面有复杂的引用关系，比如你的VIewModel或者Model引用了其他的类，你可能没有察觉，而那些类可能是Public Static的（是GC Root，不释放），或者是永远不释放的（如MainForm）引用，那就复杂了。由于你的ViewModel被那些不释放的对象引用着，而你却不知道，那就是内存泄露了。这和MVVM没有关系。

 

深入思考和继续阅读

通常.NET程序的内存泄露原因：

• Static references
• Event with missing unsubscription
• Static event with missing unsubscription
• Dispose method not invoked
• Incomplete Dispose method

有关如何避免.NET程序的内存泄露，请仔细阅读MSDN这两篇文章，详细讲述了<如何检测.NET程序内存泄露>以及<如何写高性能的托管程序>

• How to detect and avoid memory and resources leaks in .NET applications
• Writing High-Performance Managed Applications : A Primer

有关.NET的自动内存管理机制、GC机制，垃圾回收原理等深层次内容，请仔细阅读下面的内容：

• 买书《CLR Via C#(3rd Edition)》，里面有《Memory Management》这一章专门讲述了.NET CLR的自动内存管理和垃圾回收机制
• CodeProject上的文章《Memory Management Misconceptions》有助你深入理解Root, Generation 0, 1…

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分类: SilverLight