如何使用UIAlertController顯示來自UIViewController的提醒消息

Question

我試圖在我的UIViewController中使用UIAlertController顯示消息。 使用VisualStudio的2015年CTP 5 ...

使用的樣本來自：

http://forums.xamarin.com/discussion/26404/uialertcontroller-question-for-ipad http://www.hjerpbakk.com/blog/2014/11/23/from-uialertview-to-uialertcontroller-using-xamarin-and-async-await https://gist.github.com/Sankra/622e5855f95189e13d77

基於以上的樣品我有這個至今：

public partial class MyViewController : GenericViewController //inherits from UIViewController 
{ 
    ..... 
    public async override void ViewDidLoad() 
    { 
      try 
      { 

       base.ViewDidLoad(); 
       //other irrelevant code here 
       throw new Exception("Something went wrong"); 
      } 
      catch (Exception ex) 
      { 
        int result = await AlertViewControllerHelper.ShowAlertDialogAsync(this, ex.StackTrace, true); 
      } 
    } 
     ........ 
} 

我的靜態輔助等級：

public static class AlertViewControllerHelper 
{ 
public static Task<int> ShowAlertDialogAsync(UIViewController parent, string stackTrace, bool debugMode = false) 
{ 

    var taskCompletionSource = new TaskCompletionSource<int>(); 

    try 
    { 
     var alert = UIAlertController.Create("Error", stackTrace, UIAlertControllerStyle.ActionSheet); 
     if (alert.PopoverPresentationController != null) 
     { 
      alert.PopoverPresentationController.SourceView = parent.View; 
      alert.PopoverPresentationController.SourceRect = parent.View.Bounds; 
     } 

     alert.AddAction(UIAlertAction.Create("OK", UIAlertActionStyle.Default, 
      a => taskCompletionSource.SetResult(0))); 
     if (debugMode) 
     { 
      alert.AddAction(UIAlertAction.Create("Info", UIAlertActionStyle.Default, 
       a => taskCompletionSource.SetResult(1))); 
     } 

     parent.PresentViewController(alert, true, null); 

    } 
    catch (Exception ex) 
    {    
    } 
    return taskCompletionSource.Task; 
} 

運行代碼後，我的錯誤對話不顯示。 我已經完成了使用UIAlertView但UIAlertController到目前爲止沒有運氣的例子（這是我的要求）提前

謝謝...

Answer 1

此找到解決方案：
1.通ParentViewController代替當前視圖控制器（本）

public partial class MyViewController : GenericViewController //inherits from UIViewController 
{ 

    ..... 
public async override void ViewDidLoad() 
{ 
     try 
     { 

      base.ViewDidLoad(); 
      //other irrelevant code here 
      throw new Exception("Something went wrong"); 
     } 
     catch (Exception ex) 
     { 
      int actionCode = await AlertViewControllerHelper.ShowAlertDialogAsync(ParentViewController, AlertViewControllerHelper.ERRORDESCRIPTION); 

      if (actionCode == AlertViewControllerHelper.INFOACTIONCODE) 
      { 
       await AlertViewControllerHelper.ShowAlertDialogAsync(ParentViewController, string.Format("{0} : {1}", ex.Message, ex.StackTrace), actionCode); 
      } 
     } 
} 
    ........ 
} 

然後Helper方法將實施這樣的：

public static Task<int> ShowAlertDialogAsync(UIViewController parent, string stackTrace, int actionCode = 0) 
    { 
     bool isDebug = false; 

// #if DEBUG 
     isDebug = true; 
//#endif 

     var taskCompletionSource = new TaskCompletionSource<int>(); 

     var alert = UIAlertController.Create(ERROR, stackTrace, UIAlertControllerStyle.Alert); 
     if (alert.PopoverPresentationController != null) 
     { 
      alert.PopoverPresentationController.SourceView = parent.View; 
      alert.PopoverPresentationController.SourceRect = parent.View.Bounds; 
     } 

     alert.AddAction(UIAlertAction.Create("OK", UIAlertActionStyle.Default, 
      a => taskCompletionSource.SetResult(0))); 
     if (isDebug && actionCode == OKACTIONCODE) 
     { 
      alert.AddAction(UIAlertAction.Create("Info", UIAlertActionStyle.Default, 
       a => taskCompletionSource.SetResult(1))); 
     } 

     parent.PresentViewController(alert, true, null); 

     return taskCompletionSource.Task; 
    } 

Answer 2

using System; 
using UIKit; 
using System.Threading.Tasks; 

namespace Sample 
{ 

public partial class ViewController : UIViewController 
{ 

    public ViewController (IntPtr handle) : base (handle) 
    { 
    } 

    public override void ViewDidLoad() 
    { 
     base.ViewDidLoad(); 
     // Perform any additional setup after loading the view, typically from a nib. 

    } 

    public override void ViewDidAppear (bool animated) 
    { 
     base.ViewDidAppear (animated); 
     this.InvokingMethod(); 

    } 

    public static Task<bool> ShowOKCancel (UIViewController parent, string strTitle, string strMsg) 
    { 
     // method to show an OK/Cancel dialog box and return true for OK, or false for cancel 
     var taskCompletionSource = new TaskCompletionSource<bool>(); 

     var alert = UIAlertController.Create (strTitle, strMsg, UIAlertControllerStyle.ActionSheet); 
     // set up button event handlers 
     alert.AddAction (UIAlertAction.Create ("OK", UIAlertActionStyle.Default, a => taskCompletionSource.SetResult (true))); 
     alert.AddAction (UIAlertAction.Create ("Cancel", UIAlertActionStyle.Default, a => taskCompletionSource.SetResult (false))); 
     // show it 
     parent.PresentViewController (alert, true, null); 

     return taskCompletionSource.Task; 
    } 

    private async void InvokingMethod() 
    { 
     var userClickedOk = await ShowOKCancel (this, "Action Sheet Title", " It is just awesome!"); 
     // go on to use the result in some way  

     if (userClickedOk) { 
      Console.WriteLine ("Clicked on Okay"); 

     } else {     
      Console.WriteLine ("Clicked on Cancel"); 
     }; 
    } 

    public override void DidReceiveMemoryWarning() 
    { 
     base.DidReceiveMemoryWarning(); 
     // Release any cached data, images, etc that aren't in use. 
    } 
} 
}