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：

   1: namespace SilverlightApplication1.Service

   2: {

   3:     public class GlobalService

   4:     {

   5:         private static readonly GlobalService Instance = new GlobalService();

6:

   7:         static GlobalService()

   8:         {

   9:         }

10:

  11:         public static GlobalService GetInstance()

  12:         {

  13:             return Instance;

  14:         }

  15:     }

  16: }

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

   1: using System.ComponentModel;

   2: using System.Windows.Input;

   3: using SilverlightApplication1.Service;

4:

   5: namespace SilverlightApplication1.MVVM

   6: {

   7:     public class ViewModel1 : INotifyPropertyChanged

   8:     {

   9:         private GlobalService _injectSingletonService;

10:

  11:         public ViewModel1(GlobalService injectSingletonService)

  12:         {

  13:             Property1 = "test1";

  14:             Command1 = new DelegateCommand(LoadMe, CanLoadMe);

15:

  16:             _injectSingletonService = injectSingletonService;

  17:         }

18:

  19:         private string _property1;

  20:         public string Property1

  21:         {

  22:             get { return _property1; }

  23:             set

  24:             {

  25:                 _property1 = value;

26:

  27:                 if (PropertyChanged != null)

  28:                 {

  29:                     PropertyChanged(this,

  30:                         new PropertyChangedEventArgs("Property1"));

  31:                 }

  32:             }

  33:         }

34:

  35:         public ICommand Command1 { get; set; }

  36:         public event PropertyChangedEventHandler PropertyChanged;

37:

  38:         private void LoadMe(object param)

  39:         {

40:

  41:         }

42:

  43:         private bool CanLoadMe(object param)

  44:         {

  45:             return true;

  46:         }

  47:     }

  48: }

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

   1: <UserControl x:Class="SilverlightApplication1.MVVM.View1"

   2:     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

   3:     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

   4:     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"

   5:     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"

   6:     mc:Ignorable="d"

   7:     d:DesignHeight="300" d:DesignWidth="400">

8:

   9:     <Grid x:Name="LayoutRoot" Background="White">

  10:         <TextBlock Height="65" HorizontalAlignment="Left" Margin="57,82,0,0" Name="textBlock1" Text="this is view1" VerticalAlignment="Top" Width="224" FontSize="18" />

  11:         <Button Content="Button" Command="{Binding Command1}" Height="28" HorizontalAlignment="Left" Margin="55,130,0,0" Name="button1" VerticalAlignment="Top" Width="111" />

  12:         <TextBlock Height="28" HorizontalAlignment="Left" Margin="56,173,0,0" Name="textBlock2" Text="{Binding Property1}" VerticalAlignment="Top" Width="114" />

  13:     </Grid>

  14: </UserControl>

这个View1的界面是这样子的：

View1.xaml.cs代码：

   1: using System.Windows.Controls;

   2: using SilverlightApplication1.Service;

3:

   4: namespace SilverlightApplication1.MVVM

   5: {

   6:     public partial class View1 : UserControl

   7:     {

   8:         public View1()

   9:         {

  10:             InitializeComponent();

11:

  12:             this.DataContext = new ViewModel1(GlobalService.GetInstance());

  13:         }

  14:     }

  15: }

辅助类DelegateCommand源码：

   1: using System;

   2: using System.Windows.Input;

3:

   4: namespace SilverlightApplication1

   5: {

   6:     public class DelegateCommand : ICommand

   7:     {

   8:         public event EventHandler CanExecuteChanged;

9:

  10:         Func<object, bool> canExecute;

  11:         Action<object> executeAction;

  12:         bool canExecuteCache;

13:

  14:         public DelegateCommand(Action<object> executeAction,

  15:         Func<object, bool> canExecute)

  16:         {

  17:             this.executeAction = executeAction;

  18:             this.canExecute = canExecute;

  19:         }

20:

  21:         #region ICommand Members

22:

  23:         /// <summary>

24:

  25:         /// Defines the method that determines whether the command

26:

  27:         /// can execute in its current state.

28:

  29:         /// </summary>

30:

  31:         /// <param name="parameter">

32:

  33:         /// Data used by the command.

34:

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

36:

  37:         /// this object can be set to null.

38:

  39:         /// </param>

40:

  41:         /// <returns>

42:

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

44:

  45:         /// </returns>

46:

  47:         public bool CanExecute(object parameter)

  48:         {

49:

  50:             bool tempCanExecute = canExecute(parameter);

51:

52:

53:

  54:             if (canExecuteCache != tempCanExecute)

  55:             {

56:

  57:                 canExecuteCache = tempCanExecute;

58:

  59:                 if (CanExecuteChanged != null)

  60:                 {

61:

  62:                     CanExecuteChanged(this, new EventArgs());

63:

  64:                 }

65:

  66:             }

67:

68:

69:

  70:             return canExecuteCache;

71:

  72:         }

73:

74:

75:

  76:         /// <summary>

77:

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

79:

  80:         /// </summary>

81:

  82:         /// <param name="parameter">

83:

  84:         /// Data used by the command.

85:

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

87:

  88:         /// this object can be set to null.

89:

  90:         /// </param>

91:

  92:         public void Execute(object parameter)

  93:         {

94:

  95:             executeAction(parameter);

96:

  97:         }

98:

  99:         #endregion

 100:     }

 101: }

MainPage的代码：

   1: <UserControl x:Class="SilverlightApplication1.MainPage"

   2:     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

   3:     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

   4:     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"

   5:     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"

   6:     mc:Ignorable="d"

   7:     d:DesignHeight="300" d:DesignWidth="400" xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk">

8:

   9:     <Grid x:Name="LayoutRoot" Background="White">

  10:         <Button Content="Add view" Height="36" HorizontalAlignment="Left" Margin="20,31,0,0" Name="button1" VerticalAlignment="Top" Width="115" Click="button1_Click" />

  11:         <sdk:TabControl Height="197" HorizontalAlignment="Left" Margin="28,82,0,0" Name="tabControl1" VerticalAlignment="Top" Width="346">

  12:             <sdk:TabItem Header="tabItem1" Name="tabItem1">

  13:                 <Grid />

  14:             </sdk:TabItem>

  15:         </sdk:TabControl>

  16:         <Button Content="Close view" Height="35" HorizontalAlignment="Left" Margin="148,32,0,0" Name="button2" VerticalAlignment="Top" Width="108" Click="button2_Click" />

  17:     </Grid>

  18: </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()）

   1: using System;

   2: using System.Windows;

   3: using System.Windows.Controls;

   4: using SilverlightApplication1.MVVM;

5:

   6: namespace SilverlightApplication1

   7: {

   8:     public partial class MainPage : UserControl

   9:     {

  10:         public MainPage()

  11:         {

  12:             InitializeComponent();

  13:         }

14:

  15:         private void button1_Click(object sender, RoutedEventArgs e)

  16:         {

  17:             var v = new View1();

  18:             TabItem t = new TabItem {Content = v, Header = "header " + DateTime.Now.Second.ToString()};

  19:             this.tabControl1.Items.Add(t);

  20:         }

21:

  22:         private void button2_Click(object sender, RoutedEventArgs e)

  23:         {

  24:             this.tabControl1.Items.RemoveAt(0);//view1, viewModel1并没有立即释放，由GC决定何时决定。

25:

  26:             System.GC.Collect();

  27:             System.GC.WaitForPendingFinalizers();

28:

  29:             //{

  30:             //    FooContext context = new FooContext();

  31:             //    context.Load(context.MyQuery);

  32:             //}

  33:         }

  34:     }

  35: }

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

转载于:https://www.cnblogs.com/Areas/archive/2011/09/23/2186621.html