Category Archives: Errors

Errors

Xamarin Forms, Android and images – things to remember

If you are using Xamarin Forms for your next awesome cross-platform mobile app, there are things you need to remember when dealing with images for Android.

1. No folders

Even though you can group images into subfolders at root level for Windows Phone or under Resources for iOS, all images have to be inside the Drawable folder for Android. Images in folders are not used.

However, Images/picture.png still resolves on Android.

Which brings us to the obvious…

2. No duplicates

You cannot have two images with the same name in two different folders like Company1/Logo.png and Company2/Logo.png.

Because you cannot have two files with the same name in the same folder.

However, there are still problems with file names…

3. Invalid characters in file names

After reading point 2, you renamed your files and put all images into Drawable. You renamed those files with the same name to something more obvious like Company1-Logo.png and Company2-Logo.png. And it still doesn’t work.

// aapt resource value: 0x7f020020
public const int Icon = 2130837536;

Picture above: Android’s awesome resource handling code.

Due to the way resources are processed in Android, all file names are converted to C# identifiers. And you can resolve images by using their C# counterpart. This, unfortunately, means that only those file names which are valid C# identifiers are valid file names.

This means removing dashes and using underscores. This also means that your images starting with numbers are also invalid. Forget all those 1.png and 13thStreet.pngh, use some “better” names.

Till’ next time, happy coding.

Errors

Don’t use ObservableCollection.Clear on Xamarin.iOS

Xamarin.Forms are awesome, but the framework is young and there are some very annoying bugs. Consider the following common, and simple, scenario: you have a ListView bound to an ObservableCollection. If you want to clear/fill that list, e.g. you are building a search page, you will get the following errors (the numbers may vary):

MonoTouch.Foundation.MonoTouchException: Objective-C exception thrown. Name: NSInternalInconsistencyException Reason: Invalid update: invalid number of rows in section 0. The number of rows contained in an existing section after the update (1) must be equal to the number of rows contained in that section before the update (6), plus or minus the number of rows inserted or deleted from that section (1 inserted, 0 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out).

There is a simple workaround: clear the list by removing each item individually. Instead of writing:

list.Clear();

use:

while (list.Any())
    list.RemoveAt(list.Count - 1);

Happy coding :)

Errors Windows Phone

Error using the most recent version of RestSharp in wp7.

When adding RestSharp via NuGet to WP7 project, you will probably receive the following error:

File or assembly name ‘Newtonsoft.Json, Version=4.0.5.0, Culture=neutral, PublicKeyToken=30AD4FE6B2A6AEED’, or one of its dependencies, was not found.

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Errors

“Unable to create virtual directory” error message in Visual Studio 2010

The error from IIS are sometimes baffling, such as this one:

Unable to create the virtual directory. Could not find the server ‘http://localhost/xxxx’ on the local machine. Creating a virtual directory is only supported on the local IIS server.

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