魯棒的方法來從基類一般初始化派生類的字段？

Question

我正在開發一個項目，它有許多從類View派生的類，其中View提供了一些常用的方法，派生類的字段引用了該視圖的特定UI元素。例如（在C＃）：

public abstract class View 
{ 
    public virtual void Initialize(){} 
    public virtual void Activate(){} 
    public virtual void Deactivate(){} 
}  

public class MainScreenView : View 
{ 
    private ImageView portraitImageView; 
    private ImageView landscapeImageView; 

    public MainScreenView(ImageView portrait, ImageView landscape) 
    { 
     portraitImageView = portrait; 
     landscapeImageView = landscape; 
    } 

    public override Initialize() 
    { 
     base.Initialize(); 
     portraitImageView.Initialize(); // I would like to eliminate these calls! 
     landscapeImageView.Initialize(); 
    } 

    public ImageView GetPortrait() { return portraitImageView; } 
    public ImageView GetLandscape() { return landscapeImageView; } 
} 

public class ImageView : View 
{ 
    private Image image; 

    public ImageView(Image image) { this.image = image; } 
    public override void Initialize() { base.Initialize(); image.Show(); } 
    public Image GetImage() { return image; } 
} 

在這個例子中，我要對所有ImageViews調用初始化（）時MainScreenView.Initialize被調用。這感覺容易出錯並且不方便，因爲每次將新的子視圖添加到MainScreenView組合時，都必須添加Initialize（）調用。因此，我想在派生類中消除對這些調用的需求，但是我想將這些字段保留到特定於視圖的字段中。

我的想法是添加視圖基類，然後可以遞歸初始化（）的集合，如下：

public abstract class View 
{ 
    private List<View> subViews; 

    public virtual void Initialize() 
    { 
     foreach(View in subViews) { view.Initialize(); } 
    } 

    // This gets called before Initialize() is called. 
    public void AddSubViews(View[] views) 
    { 
     subViews = new List<View>(); 
     subViews.AddRange(views); 
    } 
} 

public class MainScreenView : View 
{ 
    private ImageView portraitImageView; 
    private ImageView landscapeImageView; 

    public MainScreenView() 
    { 
     portraitImageView = ???; 
     landscapeImageView = ???; 
    } 

    // Even if View.subViews had been protected instead of private, this couldn't return an element from the list because the required index is unknown. 
    public ImageView GetPortrait() { return portraitImageView; } 
    public ImageView GetLandscape() { return landscapeImageView; } 
} 

public class ImageView : View 
{ 
    private Image image; 

    public ImageView() { this.image = ??? } 
    public override void Initialize() { base.Initialize(); image.Show(); } 
    public Image GetImage() { return image; } // Even if View.subViews had been protected instead of private, this couldn't return an element from the list because the required index is unknown. 
} 

然而，因爲所有的單個子視圖現在是「匿名'（它們通過索引而不是字段名來訪問），除非我也通過派生類的構造函數添加子視圖，如我在第一個示例中所做的那樣，我無法執行傳遞給構造函數的對象與列表中的對象相同，或者從派生類的構造函數中調用AddSubViews，其中每次添加新子視圖時都手動添加子視圖...具有相同問題是在子視圖上調用Initialize（）在派生類中。

所以我的問題是：是有辦法有子視圖的所有初始化調用的視圖基類正在做，同時仍能夠提供派生類特定的元素，而無需通過引用這些元素派生類的構造函數？

Answer 1

更新：如果你想確保所有的子視圖被初始化（即沒有人忘記將它們添加到子視圖的基類列表），你可以使用反射的方法。這是主要的想法：

public interface IView // you don't need abstract class 
{ 
    void Initialize(); 
} 

使用反射來獲取它們實現IView所有類字段和被初始化：

public class View : IView 
{ 
    private IView portraitView; 
    private IView landscapeView; 

    // assign some values to sub-views 

    public virtual void Initialize() 
    { 
     var flags = BindingFlags.NonPublic | BindingFlags.Instance; 
     var subViews = from field in GetType().GetFields(flags) 
         let value = field.GetValue(this) 
         where value != null && value is IView 
         select (IView)value; 

     foreach (var subView in subViews) 
      subView.Initialize(); 
    } 
} 

這麼簡單。現在，如果有人會將IView類型的字段添加到您的課程中，則會使用其他子視圖進行初始化。

---

原來的答案：只需添加這兩種觀點基類子視圖列表：

public MainScreenView(ImageView portrait, ImageView landscape) 
{ 
    portraitImageView = portrait; 
    landscapeImageView = landscape; 
    AddSubViews(new View [] { portrait, landscape }); 
} 

也請記住，你正在重新創建子視圖每次列表，當您試圖添加新觀點：

public void AddSubViews(View[] views) 
{ 
    subViews = new List<View>(); // here 
    subViews.AddRange(views); 
} 

我認爲這是較好的一類場初始化期間只有一次創建子視圖列表：

private readonly List<View> subViews = new List<View>(); 

public void AddSubViews(params View[] views) // you can use params here 
{ 
    subViews.AddRange(views); 
} 

現在，你根本就打電話

AddSubViews(portrait, landscape); 

Answer 2

您可以使用以下模式：

public abstract class View 
{ 
    private IEnumerable<View> SubViews { get; } 

    protected View(params View[] subViews) 
    { 
     SubViews = subViews; 
    } 

    public void Initialize() 
    { 
     OnInitialize(); 

     foreach (var view in SubViews) 
     { 
      view.Initialize(); 
     } 
    } 

    protected abstract void OnInitialize(); 
} 

現在你具體的意見將是這樣的：

public class MainScreenView : View 
{ 
    private readonly ImageView portraitImageView; 
    private readonly ImageView landscapeImageView; 

    public MainScreenView(ImageView portrait, ImageView landscape) 
     : base(portrait, landscape) 
    { 
     portraitImageView = portrait; 
     landscapeImageView = landscape; 
    } 

    protected override void OnInitialize() { } 
    public ImageView GetPortrait() { return portraitImageView; } 
    public ImageView GetLandscape() { return landscapeImageView; } 
} 

public class ImageView : View 
{ 
    private readonly Image image; 

    public ImageView(Image image) 
     : base() 
    { 
     this.image = image; 
    } 

    protected override void OnInitialize() { image.Show(); } 
    public string GetImage() { return image; } 
} 

最後，

var main = new MainScreenView(new ImageView(portraitImage), new ImageView(landScapeImage)); 
main.Initialize(); 

將正確初始化所有視圖。