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Tips for Updating Code to the Unified API

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When updating older Xamarin solutions to the Unified API, the following errors might be encountered.

NSInvalidArgumentException Could Not Find storyboard Error

There is a bug in the current version of Visual Studio for Mac that can occur after using the automated migration tool to convert your project to the Unified APIs. After the update, if you get an error message in the form:

Objective-C exception thrown. Name: NSInvalidArgumentException Reason: Could not find a storyboard named 'xxx' in bundle NSBundle...

You can do the following to solve this issue, locate the following build target file:

/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/2.1/Xamarin.iOS.Common.targets

In this file you need to find the following target declaration:

<Target Name="_CopyContentToBundle"
        Inputs = "@(_BundleResourceWithLogicalName)"
        Outputs = "@(_BundleResourceWithLogicalName -> '$(_AppBundlePath)%(LogicalName)')" >

And add the DependsOnTargets="_CollectBundleResources" attribute to it. Like this:

<Target Name="_CopyContentToBundle"
        DependsOnTargets="_CollectBundleResources"
        Inputs = "@(_BundleResourceWithLogicalName)"
        Outputs = "@(_BundleResourceWithLogicalName -> '$(_AppBundlePath)%(LogicalName)')" >

Save the file, reboot Visual Studio for Mac, and do a clean & rebuild of your project. A fix for this issue should be released by Xamarin shortly.

Useful Tips

After using the migration tool, you may still get some compiler errors requiring manual intervention. Some things that might need to be manually fixed include:

  • Comparing enums might require an (int) cast.

  • NSDictionary.IntValue now returns an nint, there is an Int32Value which can be used instead.

  • nfloat and nint types cannot be marked const; static readonly nint is a reasonable alternative.

  • Things that used to be directly in the MonoTouch. namespace are now generally in the ObjCRuntime. namespace (e.g.: MonoTouch.Constants.Version is now ObjCRuntime.Constants.Version).

  • Code that serializes objects may break when attempting to serialize nint and nfloat types. Be sure to check your serialization code works as expected after migration.

  • Sometimes the automated tool misses code inside #if #else conditional compiler directives. In this case you'll need to make the fixes manually (see the common errors below).

  • Manually exported methods using [Export] may not be automatically fixed by the migration tool, for example in this code snippert you must manually update the return type to nfloat:

    [Export("tableView:heightForRowAtIndexPath:")]
public nfloat HeightForRow(UITableView tableView, NSIndexPath indexPath)

  • The Unified API does not provide an implicit conversion between NSDate and .NET DateTime because it's not a lossless conversion. To prevent errors related to DateTimeKind.Unspecified convert the .NET DateTime to local or UTC before casting to NSDate.

  • Objective-C category methods are now generated as extension methods in the Unified API. For example, code that previously used UIView.DrawString would now reference NSString.DrawString in the Unified API.

  • Code using AVFoundation classes with VideoSettings should change to use the WeakVideoSettings property. This requires a Dictionary, which is available as a property on the settings classes, for example:

    vidrec.WeakVideoSettings = new AVVideoSettings() { ... }.Dictionary;

  • The NSObject .ctor(IntPtr) constructor has been changed from public to protected (to prevent improper use).

  • NSAction has been replaced with the standard .NET Action. Some simple (single parameter) delegates have also been replaced with Action<T>.

Finally, refer to the Classic v Unified API differences to look up changes to APIs in your code. Searching this page will help find Classic APIs and what they've been updated to.

Note

The MonoTouch.Dialog namespace remains the same after migration. If your code uses MonoTouch.Dialog you should continue to use that namespace - do not change MonoTouch.Dialog to Dialog!

Common Compiler Errors

Other examples of common errors are listed below, along with the solution:

Error CS0012: The type 'MonoTouch.UIKit.UIView' is defined in an assembly that is not referenced.

Fix: This usually means the project references a component or NuGet package that has not been built with the Unified API. You should delete and re-add all Components and NuGet packages. If this does not fix the error, the external library may not yet support the Unified API.

Error MT0034: Cannot include both 'monotouch.dll' and 'Xamarin.iOS.dll' in the same Xamarin.iOS project - 'Xamarin.iOS.dll' is referenced explicitly, while 'monotouch.dll' is referenced by 'Xamarin.Mobile, Version=0.6.3.0, Culture=neutral, PublicKeyToken=null'.

Fix: Delete the component that is causing this error and re-add to the project.

Error CS0234: The type or namespace name 'Foundation' does not exist in the namespace 'MonoTouch'. Are you missing an assembly reference?

Fix: The automated migration tool in Visual Studio for Mac should update all MonoTouch.Foundation references to Foundation, however in some instances these will need to be updated manually. Similar errors may appear for the other namespaces previously contained in MonoTouch, such as UIKit.

Error CS0266: Cannot implicitly convert type 'double' to 'System.float'

Fix: change type and cast to nfloat. This error may also occur for the other types with 64-bit equivalents (such as nint, )

nfloat scale = (nfloat)Math.Min(rect.Width, rect.Height);

Error CS0266: Cannot implicitly convert type 'CoreGraphics.CGRect' to 'System.Drawing.RectangleF'. An explicit conversion exists (are you missing a cast?)

Fix: Change instances to RectangleF to CGRect, SizeF to CGSize, and PointF to CGPoint. The namespace using System.Drawing; should be replaced with using CoreGraphics; (if it isn't already present).

error CS1502: The best overloaded method match for 'CoreGraphics.CGContext.SetLineDash(System.nfloat, System.nfloat[])' has some invalid arguments

Fix: Change array type to nfloat[] and explicitly cast Math.PI.

grphc.SetLineDash (0, new nfloat[] { 0, 3 * (nfloat)Math.PI });

Error CS0115: `WordsTableSource.RowsInSection(UIKit.UITableView, int)' is marked as an override but no suitable method found to override

Fix: Change the return value and parameter types to nint. This commonly occurs in method overrides such as those on UITableViewSource, including RowsInSection, NumberOfSections, GetHeightForRow, TitleForHeader, GetViewForHeader, etc.

public override nint RowsInSection (UITableView tableview, nint section) {

Error CS0508: WordsTableSource.NumberOfSections(UIKit.UITableView): return type must be 'System.nint' to match overridden member UIKit.UITableViewSource.NumberOfSections(UIKit.UITableView)

Fix: When the return type is changed to nint, cast the return value to nint.

public override nint NumberOfSections (UITableView tableView)
{
    return (nint)navItems.Count;
}

Error CS1061: Type 'CoreGraphics.CGPath' does not contain a definition for 'AddElipseInRect'

Fix: Correct spelling to AddEllipseInRect. Other name changes include:

  • Change 'Color.Black' to NSColor.Black.
  • Change MapKit 'AddAnnotation' to AddAnnotations.
  • Change AVFoundation 'DataUsingEncoding' to Encode.
  • Change AVFoundation 'AVMetadataObject.TypeQRCode' to AVMetadataObjectType.QRCode.
  • Change AVFoundation 'VideoSettings' to WeakVideoSettings.
  • Change PopViewControllerAnimated to PopViewController.
  • Change CoreGraphics 'CGBitmapContext.SetRGBFillColor' to SetFillColor.

Error CS0546: cannot override because `MapKit.MKAnnotation.Coordinate' does not have an overridable set accessor (CS0546)

When creating a custom annotation by subclassing MKAnnotation the Coordinate field has no setter, only a getter.

The Fix

  • Add a field to keep track of the coordinate
  • return this field in the getter of the Coordinate property
  • Override the SetCoordinate method and set your field
  • Call SetCoordinate in your ctor with the passed in coordinate parameter

It should look similar to the following:

class BasicPinAnnotation : MKAnnotation
{
    private CLLocationCoordinate2D _coordinate;

    public override CLLocationCoordinate2D Coordinate
    {
        get
        {
            return _coordinate;
        }
    }

    public override void SetCoordinate(CLLocationCoordinate2D value)
    {
        _coordinate = value;
    }

    public BasicPinAnnotation (CLLocationCoordinate2D coordinate)
    {
        SetCoordinate(coordinate);
    }
}