如何在MonoTouch中为继承的视图创建UIAppearance代理？

Posted 2021-04-21

我创建了一个UIButton的子类，它充当UIBarButtonItem中的自定义Back按钮：

 - - - - - - - - - - - - - - - - - 
|         UIBarButtonItem         |

|     ------------------------    |
     /                       |
|     BackButton : UIButton |    |
      ------------------------
|  _  _  _  _  _  _  _  _  _  _  _|

当我将我的代码切换到使用UIAppearance时，我注意到BackButton.Appearance是毫无疑问的，继承自UIButton.Appearance，因此更改它将改变整个应用程序中的所有UIButtons，而不仅仅是我的自定义按钮。

我知道我可以使用AppearanceWhenContainedIn但是，因为UIBarButtonItem不是外观容器，我必须在它们之间插入另一个视图以识别后退按钮，我不想这样做。

如何为我的自定义UIAppearance子类提供UIButton代理，该子类具有UIButton.UIButtonAppearance中的所有可用方法？我注意到它的构造函数是内部的。

答案

虽然可能有一个更简单的答案，但我最终直接从UIAppearance继承并从MonoDevelop C＃反汇编程序中复制粘贴相关的UIButton和UIButton+UIButtonAppearance绑定实现，并在此处和那里修复内部字段。

在BackButton内：

static readonly IntPtr class_ptr = Class.GetHandle(typeof(BackButton));

public new static BackButtonAppearance Appearance
{
    get {
        return new BackButtonAppearance (Messaging.IntPtr_objc_msgSend (class_ptr, UIAppearance.SelectorAppearance));
    }
}

public new static BackButtonAppearance AppearanceWhenContainedIn (params Type[] containers)
{
    return new BackButtonAppearance (UIAppearance.GetAppearance (class_ptr, containers));
}

嵌套的BackButtonAppearance：

public class BackButtonAppearance : UIAppearance {
    public BackButtonAppearance(IntPtr handle) : base(handle) { }

    // These are copied from UIButton disassembly:

    static readonly IntPtr selSetBackgroundImageForState_ = Selector.GetHandle ("setBackgroundImage:forState:");
    static readonly IntPtr selSetTitleShadowColorForState_ = Selector.GetHandle ("setTitleShadowColor:forState:");            
    static readonly IntPtr selSetTitleColorForState_ = Selector.GetHandle ("setTitleColor:forState:");

    // These are copied from UIButton+UIButtonAppearance disassembly,
    // with internal UIButton.selSet* fields replaced by fields declared above.

    [Export ("setBackgroundImage:forState:"), CompilerGenerated]
    public virtual void SetBackgroundImage (UIImage image, UIControlState forState)
    {
        UIApplication.EnsureUIThread ();
        if (this.IsDirectBinding) {
            Messaging.void_objc_msgSend_IntPtr_UInt32 (base.Handle, selSetBackgroundImageForState_, (image != null) ? image.Handle : IntPtr.Zero, (uint)forState);
        } else {
            Messaging.void_objc_msgSendSuper_IntPtr_UInt32 (base.SuperHandle, selSetBackgroundImageForState_, (image != null) ? image.Handle : IntPtr.Zero, (uint)forState);
        }
    }


    [Export ("setTitleColor:forState:"), CompilerGenerated]
    public virtual void SetTitleColor (UIColor color, UIControlState forState)
    {
        UIApplication.EnsureUIThread ();
        if (this.IsDirectBinding) {
            Messaging.void_objc_msgSend_IntPtr_UInt32 (base.Handle, selSetTitleColorForState_, (color != null) ? color.Handle : IntPtr.Zero, (uint)forState);
        } else {
            Messaging.void_objc_msgSendSuper_IntPtr_UInt32 (base.SuperHandle, selSetTitleColorForState_, (color != null) ? color.Handle : IntPtr.Zero, (uint)forState);
        }
    }

    [Export ("setTitleShadowColor:forState:"), CompilerGenerated]
    public virtual void SetTitleShadowColor (UIColor color, UIControlState forState)
    {
        UIApplication.EnsureUIThread ();
        if (this.IsDirectBinding) {
            Messaging.void_objc_msgSend_IntPtr_UInt32 (base.Handle, selSetTitleShadowColorForState_, (color != null) ? color.Handle : IntPtr.Zero, (uint)forState);
        } else {
            Messaging.void_objc_msgSendSuper_IntPtr_UInt32 (base.SuperHandle, selSetTitleShadowColorForState_, (color != null) ? color.Handle : IntPtr.Zero, (uint)forState);
        }
    }
}

这允许我带来我的自定义视图以支持UIAppearance风格的API。

另一答案

为完整性添加答案。

使用BackButton.GetAppearance<BackButton>()而不是BackButton.Appearance。