Xamarin - Does Android Drawable Exist?

Question

In a Xamarin Forms (3.0) application, what method(s) would I use to tell if a drawable resource exists in my Android project from shared project code?

In iOS, I can use NSFileManager to see if the file exists in my iOS project's "Resources" folder:

#if __IOS__
private bool DoesImageExist(string image)
{
    //WORKS
    return Foundation.NSFileManager.DefaultManager.FileExists(image);
}
#endif

In Android, I thought it should be part of the Assembly Resources, but that just returns my App.xaml file.

#if __ANDROID__
private bool DoesImageExist(string image)
{
    //DOES NOT WORK
    if(MyApp.Current?.GetType() is Type type)
        foreach (var res in Assembly.GetAssembly(type).GetManifestResourceNames())
        {
            if (res.Equals(image, StringComparison.CurrentCultureIgnoreCase))
                return true;
        }
    return false;
}
#endif

Curtis Shipley Curtis Shipley · Accepted Answer · 2018-07-27T20:52:02

How to specifically check if a drawable exists by name in android would work like something this:

#if __ANDROID__
public bool DoesImageExist(string image)
{
    var context = Android.App.Application.Context;
    var resources = context.Resources;
    var name = Path.GetFileNameWithoutExtension(image);
    int resourceId = resources.GetIdentifier(name, "drawable", context.PackageName);

    return resourceId != 0;
}
#endif

If your code is in a pcl or .net standard assembly, you will have to create an abstraction. Some kind of Ioc library works well for this. You can also have Android or iOS implement the abstract interface and make that available as a singleton somewhere. It's not as elegant, but it would work.

Basically you would implement something like this:

public interface IDrawableManager
{
    bool DoesImageExist(string path);
}

Then have two implementations:

public class DroidDrawableManager : IDrawableManager
{
        var context = Android.App.Application.Context;
        var resources = context.Resources;
        var name = Path.GetFileNameWithoutExtension(image);
        int resourceId = resources.GetIdentifier(name, "drawable", context.PackageName);

        return resourceId != 0;
}

public class IOSDrawableManager : IDrawableManager
{
    public bool DoesImageExist(string image)
    {
        return Foundation.NSFileManager.DefaultManager.FileExists(image);
    }
}

I've uploaded a working sample to github:

https://github.com/curtisshipley/ResourceExists

Xamarin - Does Android Drawable Exist?

1 Answers