不能理解INotifyPropertyChanged的實現

Question

我只是C＃中的一個新手，我在MSDN博客上閱讀INotifyPropertyChanged Event Handler並在這裏搜索「stackoverflow」。但我真的不明白如何在代碼中實現它，以及如何將事件和屬性綁定在一起。

我已經與INotifyPropertyChanged取得了BindingClass，代碼爲：

namespace Testing.Pages 
{ 
    class BindingClass : INotifyPropertyChanged 
    { 
    private string _setting; 
    public event PropertyChangedEventHandler PropertyChanged; 

    public BindingClass() 
    { 

    } 

    public BindingClass(string value) 
    { 
     _setting = value; 
    } 

    public string SettingProperty 
    { 
     get { return _setting; } 
     set 
     { 
      _setting = value; 
      // calling OnPropertyChanged whenever the property gets updated 

     } 
    } 

    protected void OnPropertyChanged([CallerMemberName] string _setting = "") 
    { 
     PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(_setting)); 
    } 
    } 
} 

SettingsPage.xaml

<TextBlock x:Name="PopupText" 
       Grid.Row="0" 
       HorizontalAlignment="Center" 
       VerticalAlignment="Center" 
       Margin="0,0,0,20" 
       Text="Your theme will be updated next time you start the app." 
       TextWrapping="Wrap" 
       Visibility="Collapsed"> 
     <TextBlock.Resources> 
      <Storyboard x:Name="popup_animate"> 
       <DoubleAnimation Duration="0:0:2" 
           Storyboard.TargetName="PopupText" 
           AutoReverse="True" 
           From="0.0" 
           To="1.0" 
           BeginTime="{x:Bind }" 
           Storyboard.TargetProperty="(TextBlock.Opacity)" 
         ></DoubleAnimation> 
      </Storyboard> 
     </TextBlock.Resources> 
    </TextBlock> 
<TextBlock Text="Change Theme?" 
        Margin="10,10,0,0"></TextBlock> 
     <RadioButton x:Name="DarkTheme_btn" 
        Click="ChangeTheme_btn_Click" 
        Content="Dark Theme" 
        Margin="10,0,0,0" 
        GroupName="theme"></RadioButton> 
     <RadioButton x:Name="LightTheme_btn" 
        Click="ChangeTheme_btn_Click" 
        Content="Light Theme" 
        Margin="10,0,0,0" 
        GroupName="theme"></RadioButton> 

和代碼隱藏文件SettingsPage.xaml.cs是：

namespace Testing.Pages 
{ 

/// <summary> 
/// An empty page that can be used on its own or navigated to within a Frame. 
/// </summary> 
    public sealed partial class SettingsPage : Page 
    { 
    BindingClass notifyProperty = new BindingClass(); 

    public SettingsPage() 
    { 
     this.InitializeComponent(); 
     NavigationCacheMode = NavigationCacheMode.Enabled; 
    } 

    private void ChangeTheme_btn_Click(object sender, RoutedEventArgs e) 
    { 
     DataContext = notifyProperty; 
     int notifySettings = 0; 
     if ((bool)DarkTheme_btn.IsChecked) 
     { 
      notifySettings = 2; 
      AppSettings.saveThemeSettings(notifySettings); 
      PopupText.Visibility = Visibility.Visible; 
      popup_animate.Begin(); 
     } 
     else if ((bool)LightTheme_btn.IsChecked) 
     { 
      notifySettings = 1; 
      AppSettings.saveThemeSettings(notifySettings); 
      PopupText.Visibility = Visibility.Visible; 
      popup_animate.Begin(); 
     } 
    } 
    } 
} 

我已經使用了int notifySettings改變LocalSettingsFolder應用程序的設置和應用程序每次重新啓動在App.xaml加載設置。每當我更改設置時，我都會調用另一個class中的功能，並且它會更改設置，當我單擊SettingsPage.xaml中的這兩個radiobuttons中的一個時，將播放animation。這是舊的方法。
現在我想將這些事件綁定在一起，這樣我就不必使用int notifySettings和PopupText動畫，因爲它在每次更新Theme Settings時都會播放。這是我如何也可以瞭解INotifyPropertyChanged Event。
int notifySettings通過一個int值來相應地更改設置。 1 = LightTheme和2 = DarkTheme。

這裏是Settings Class：

namespace Testing.Pages 
{ 
    class AppSettings 
    { 
    public static void saveThemeSettings(int value) 
    { 
     ApplicationDataContainer themeSettings = ApplicationData.Current.LocalSettings; 
     StorageFolder localFolder = ApplicationData.Current.LocalFolder; 
     themeSettings.Values["AppThemeSetting"] = value.ToString(); 
    } 

    public static string readThemeSettings() 
    { 
     ApplicationDataContainer localSettings = ApplicationData.Current.LocalSettings; 
     StorageFolder localFolder = ApplicationData.Current.LocalFolder; 
     string appSettingsString = "error, nothing found"; 
     if (localSettings.Values.ContainsKey("AppThemeSetting")) 
     { 
      appSettingsString = localSettings.Values["AppThemeSetting"]?.ToString(); 
     } 
     return appSettingsString; 
    } 

    public static void removeLocalSettings(string settingValue) 
    { 
     ApplicationData.Current.LocalSettings.Values.Remove(settingValue); 
    } 

    } 

} 

如果仍然有任何含糊之處，請讓我知道，我可以嘗試進一步解釋。我希望有人能幫助我。

更新：
我根據答案由丹尼Bogers但需要Animation不啓動，我認爲這是因爲該功能甚至不被稱爲修改了自己的項目。我做了一些更改並嘗試自行完成，但並沒有真正實現，所以我將使用自己的方法來進行更改，直到其他人提出解決方案。

Answer 1

的的PropertyChanged需要知道哪些屬性更改，所以你必須通過它的名字。

使它看起來像這樣：

public string SettingProperty 
{ 
    get { return _setting; } 
    set 
    { 
     if(_setting != value) // Or String.Equals(_setting, value, ...) 
     { 
      _setting = value; 
      OnPropertyChanged(); // Invoke using no argument. 
     } 
    } 
} 

protected void OnPropertyChanged([CallerMemberName] string propertyName = "") 
{ 
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName)); 
} 

的OnPropertyChanged方法使用它的參數CallerMemberName屬性，該屬性也是可選的。這意味着編譯器將使用這個參數並將iith替換爲調用者的實際名稱。所以不要自己傳遞任何價值。

它相當於PropertyChanged("SettingProperty")。然而屬性使折射器安全。

關於你的問題的其餘部分：我相信這個問題本身帶來太多問題，並且包含至少一個以上的問題。所以一旦你修復了屬性改變的部分，而是問了一個具體問題的新問題。

Answer 2

我不是最擅長解釋的東西，我希望你能得到它的要點！ 我也沒有時間來正確地測試它，但是這應該可以完成這項工作。

您可以通過+=語法訂閱事件。現在，無論何時提出事件，所有訂戶都會被解僱。在這種情況下，一個PropertyChangedEventArgs的實例。這允許您的訂戶根據給定的EventArgs的值而行爲不同（您也可以將EventArgs的空實例傳遞給您的訂戶，這意味着您的訂戶不會根據EventArgs中的值進行任何操作）。

一些細微的變化：

• 增加了對主題的枚舉。檢查選擇哪個主題時添加類型安全性。這比檢查硬編碼字符串要好。

• 無法找到ThemeSetting時添加了異常。您可以在try/catch塊中相應地處理異常。這再次比檢查硬編碼字符串更好。

• 爲您的應用程序密鑰添加了一個常量字符串。與前面兩點一樣，這將防止由於錯字造成的運行時錯誤/爲您提供一個集中位置來管理值。

  namespace Testing.Pages 
  { 
      public enum Themes 
      { 
       Light = 1, 
       Dark = 2 
      } 
  } 
  
  namespace Testing.Pages 
  { 
      public class ThemeSettingNotFoundException : Exception 
      { 
       public ThemeSettingNotFoundException() : base("error, nothing found") 
       { 
       } 
      } 
  
  } 
  
  namespace Testing.Pages 
  { 
      class BindingClass : INotifyPropertyChanged 
      { 
       private string _setting; 
       public event PropertyChangedEventHandler PropertyChanged; 
  
       public BindingClass() { 
  
       } 
  
       public BindingClass(string value) { 
        _setting = value; 
       } 
  
       public string SettingProperty 
       { 
        get { return _setting; } 
        set 
        { 
         if(!_setting.Equals(value)){ 
          _setting = value; 
          OnPropertyChanged(); 
         } 
        } 
       } 
  
       protected void OnPropertyChanged([CallerMemberName] string _setting = "") { 
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(_setting)); 
       } 
      } 
  } 
  
  
  namespace Testing.Pages 
  { 
  
      /// <summary> 
      /// An empty page that can be used on its own or navigated to within a Frame. 
      /// </summary> 
      public sealed partial class SettingsPage : Page 
      { 
       BindingClass notifyProperty = new BindingClass(); 
  
       public SettingsPage() { 
        this.InitializeComponent(); 
        NavigationCacheMode = NavigationCacheMode.Enabled; 
  
        //Subscribe to the PropertyChanged event 
        notifyProperty.PropertyChanged += OnThemeSettingChanged; 
       } 
  
       private void ChangeTheme_btn_Click(object sender, RoutedEventArgs e) { 
        DataContext = notifyProperty; 
        SaveThemeSettings(); 
       } 
  
       private void SaveThemeSettings() 
       { 
        var notifySettings = 0; 
        if ((bool)DarkTheme_btn.IsChecked) 
         notifySettings = 2; 
        else if ((bool)LightTheme_btn.IsChecked) 
         notifySettings = 1; 
  
        //Only save theme settings when a button was checked 
        if (notifySettings != 0) 
         AppSettings.saveThemeSettings((Themes)notifySettings); 
       } 
  
       private void OnThemeSettingChanged(object sender, PropertyChangedEventArgs args) 
       { 
        PopupText.Visibility = Visibility.Visible; 
        popup_animate.Begin(); 
       } 
      } 
  } 
  
  
  namespace Testing.Pages 
  { 
      class AppSettings 
      { 
       private const string ThemeSettingKey = "AppThemeSetting"; 
  
       public static void saveThemeSettings(Themes theme) { 
        ApplicationDataContainer themeSettings = ApplicationData.Current.LocalSettings; 
        themeSettings.Values[ThemeSettingKey] = theme.ToString(); 
       } 
  
       public static Themes readThemeSettings() { 
        ApplicationDataContainer localSettings = ApplicationData.Current.LocalSettings; 
        if (!localSettings.Values.ContainsKey(ThemeSettingKey)) 
         throw new ThemeSettingNotFoundException(); 
        var appSettingsString = localSettings.Values[ThemeSettingKey]; 
        return (Themes)Enum.Parse(typeof(Themes), appSettingsString); 
       } 
  
       public static void removeLocalSettings(string settingValue) { 
        ApplicationData.Current.LocalSettings.Values.Remove(settingValue); 
       } 
      } 
  }