如何在 DialogViewController 上将背景设置为透明 [英] How to set the background to transparent on a DialogViewController

问题描述

当我将 MonoTouch.Dialog 背景色设置为 uiclear(transparent) 时，它抛出异常，为什么?以及如何将其设置为透明.

When I set the MonoTouch.Dialog background color to uiclear(transparent), it throw an exception, why? and How to set it to transparent.

未处理的异常:System.NullReferenceException:对象引用未设置到 MyDialogViewController.LoadView () [0x00016] in MyDialogViewController.cs 中的对象实例:ParentViewController.View.BackgroundColor = UIColor.Clear

Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object MyDialogViewController.LoadView () [0x00016] in MyDialogViewController.cs: ParentViewController.View.BackgroundColor = UIColor.Clear

public class MyDialogViewController: DialogViewController
{
    public MyDialogViewController (RootElement root)  : base (root) 
    {
    }

    public override void LoadView() 
    {
        base.LoadView ();
        this.TableView.BackgroundColor = UIColor.Clear;
    ParentViewController.View.BackgroundColor = UIColor.Clear;

    }
}


    public void xxxxx(){
      var menu = new RootElement(""){
            new Section ("Demo"){
                new EntryElement("Name", "",""),
            },
        };

        var menuDVC = new MyDialogViewController (menu) {
            Autorotate = true
        };



        this.View.AddSubview(menuDVC.View);
}

推荐答案

NullReferenceException 很可能发生，因为 ParentViewController 是 null.

The NullReferenceException most likely occurs because ParentViewController is null.

根据您的 MyDialogViewController 如何显示，这可能是由于使用了错误的属性和最近的 iOS5，更改:

Depending on how your MyDialogViewController is showed this might be due to using the wrong property and a recent, iOS5, change:

在 iOS 5.0 之前，如果视图没有父视图控制器并且正在呈现，则将返回呈现视图控制器.在 iOS 5 上，此行为不再发生.相反，使用presentingViewController 属性来访问呈现视图控制器.

Prior to iOS 5.0, if a view did not have a parent view controller and was being presented, the presenting view controller would be returned. On iOS 5, this behavior no longer occurs. Instead, use the presentingViewController property to access the presenting view controller.

但是，如果 MyDialogViewController 是窗口的 RootViewController，那么这些属性为 null 是正常的.在这种情况下，只需在 TableView 上使用 UIColor.Clear 即可获得黑色背景(我在那里什么都没有)，因此它对于 MT.D 部分应该足够了.如果您有父级，则可以在显示 MyDialogViewController 之前尝试将其背景颜色设置为清除(如果需要).

However if the MyDialogViewController is the window's RootViewController then it's normal for those properties to be null. In this case simply using UIColor.Clear on the TableView get me a black background (I had nothing there) so it should be enough for MT.D part. If you have a parent then you can try to set it's background color to clear (if needed) before displaying your MyDialogViewController.

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