Archive for the ‘Xamarin’ Category

I ran into this issue this week. I would define the Source as a URL and then, nothing…

It turns out, with FFImageLoading, an indispensable Xamarin.Forms plugin available via NuGet, you must also set the ErrorPlaceholder property if loading your image from a URL. That did the trick – images started loading perfectly!

I’ve reported what I think is a bug. I haven’t yet looked at their code.

Here’s an example of how I fixed it:

Working Code:

<ff:CachedImage 
    Source="{Binding ModelImageUrl}"
    ErrorPlaceholder="icon_errorloadingimage"
    DownsampleToViewSize="True"
    RetryCount="3"
    RetryDelay="1000"
    WidthRequest="320"
    HeightRequest="240"
    Aspect="AspectFit"
    HorizontalOptions="Center" 
    VerticalOptions="Center" />

Non-Working Code, note the missing ErrorPlaceholder property:

<ff:CachedImage 
    Source="{Binding ModelImageUrl}"
    DownsampleToViewSize="True"
    RetryCount="3"
    RetryDelay="1000"
    WidthRequest="320"
    HeightRequest="240"
    Aspect="AspectFit"
    HorizontalOptions="Center" 
    VerticalOptions="Center" />

I hope that helps others with the same issue. Enjoy!

I had the need today to display strikethrough text in a Xamarin Forms app. The built-in label control didn’t support such formatting. So, leaning on Unicode’s strikethrough character set, I wrote a function to convert any string to a strikethrough string. To be fair, this works great for the normal character set, so I feel it’s good for most things. Please let me know if your mileage varies.

Business case: I needed to show a “Was some dollar amount” value. Like “Was $BLAH, and Now BLAH!”

In my class, I simply called into my strikethrough converter, as follows:

The property:

public string StrikeThroughValueText => StrikeThroughValue.HasValue ? $"{ConvertToStrikethrough(StrikeThroughValue.Value.ToString("C"))}" : "???";

The function:

private string ConvertToStrikethrough(string stringToChange)
{
    var newString = "";
    foreach (var character in stringToChange)
    {
        newString += $"{character}\u0336";
    }
 
    return newString;
}

Enjoy! I hope this helps you 🙂

Link: More about why this works: Combining Long Stroke Overlay.

I ran into this issue today when debugging on Android, so posting what took an hour to figure out 🙂 This is for when you’re getting a null reference exception when attempting to scan. I was following the instructions here, and then, well, it wouldn’t work 🙂

Rather than using the Dependency Resolver, you’ll need to pass in the Application Context from Android. So, in the App, create a static reference to the IQrCodeScanner,, as follows:

	public partial class App : Application
	{
 
	    public static IQrCodeScanningService QrCodeScanningService;

Then, populate that static instance from the Android app, as follows:

App.QrCodeScanningService = new QrCodeScanningService(this);
global::Xamarin.Forms.Forms.Init(this, bundle);
LoadApplication(new App());

Obviously you’ll also need a matching constructor, like so:

public class QrCodeScanningService : IQrCodeScanningService
{
    private readonly Context _context;
 
    public QrCodeScanningService(Context context)
    {
        _context = context;
    }

This solved the problem like magic for me. I hope it helps you, too!

P.S. Make sure you have the CAMERA permission. I’ve also read you may also need the FLASHLIGHT permission, although I’m not entirely sure that’s required.

So I had to deal with this recently. There were many examples out there, many of which didn’t work. Sooo, I’m blogging my code example so others don’t remain stuck 🙂

In short:

  1. In the XAML, add a CommandParameter binding, and wire up the Clicked event handler.
  2. In the C# Event Handler: Read the (sender as Button).CommandParameter and it’ll be the bound object. Cast / parse accordingly.

XAML (condensed):

<ListView x:Name=”LocationsListView”
ItemsSource=”{Binding Items}”
VerticalOptions=”FillAndExpand”
HasUnevenRows=”true”
RefreshCommand=”{Binding LoadLocationsCommand}”
IsPullToRefreshEnabled=”true”
IsRefreshing=”{Binding IsBusy, Mode=OneWay}”
Refreshing=”LocationsListView_OnRefreshing”
CachingStrategy=”RecycleElement”>
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Orientation=”Horizontal” Padding=”5″>
<StackLayout WidthRequest=”64″>
<Button
CommandParameter=”{Binding Id}”
BackgroundColor=”#4CAF50″
Clicked=”MapButtonClicked”
Text=”Map”
HorizontalOptions=”FillAndExpand”></Button>
</StackLayout>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>

C#:

protected void MapButtonClicked(object sender, EventArgs e)
{
var selectedLocation = _viewModel.Items.First(item =>
item.Id == int.Parse((sender as Button).CommandParameter.ToString()));

Utility.LaunchMapApp(selectedLocation.Latitude, selectedLocation.Longitude);
}

As part of my .NET 301 Advanced class at the fantastic Eleven Fifty Academy, I teach Xamarin development. It’s sometimes tough, as every student has a different machine. Some have PCs, others have Macs running Parallels or Bootcamp. Some – many – have Intel processors, while others have AMD. I try to recommend students come to the class with Intel processors, due to the accelerated Android emulator benefit Intel’s HAXM – Hardware Acceleration Manager – provides. This blog entry is a running list of how I’ve solved getting the emulator running on so many machines. I hope the list helps you, too.

This list will be updated from time to time, as I find new bypasses. At this time, the list is targeted primarily for machines with an Intel processor. Those with AMD and Windows are likely stuck with the ARM emulators. Umm, sorry. I welcome solutions, there, too, please!

Last updated: December 4, 2017

Make sure you’re building from a path that’s ultimate length is less than 248 characters.

That odd Windows problem of long file paths bites us again here. Many new developers tend to build under c:\users\username\documents\Visual Studio 2017\projectname. Add to that the name of the project, and all its subfolders, and the eventual DLLs and executable are out of reach of various processes.

I suggest in this case you have a folder such as c:\dev\ and build your projects under there. That’s solved many launch and compile issues.

Use the x86 emulators.

If you have an Intel processor, then use the x86 and x64 based emulators instead of ARM. They’re considerably faster, as long as you have a) an Intel processor with virtualization abilities, which I believe all or most modern Intel processors do, and b) Intel’s HAXM installed.

Make sure VTI-X / Hardware Virtualization is enabled.

Intel’s HAXM – which you can download here – won’t run if the processor’s virtualization is disabled. You need to tackle this in the BIOS. That varies per machine. Many devices seem to chip with the feature disabled. Enabling it will enable HAXM to work.

Uninstall the Mobile Development with .NET Workload using the Visual Studio Installer, and reinstall.

Yes, I’m suggesting Uninstall + Reinstall. This has worked well in the class. Go to Start, then Visual Studio Installer, and uncheck the box. Restart afterwards. Then reinstall, and restart.

Mobile Development Workload Screenshot

Use the Xamarin Android SDK Manager.

The Xamarin team has built a much better Android SDK Manager than Google’s. It’s easy to install HAXM, update Build Tools and Platforms, and so forth. Use it instead and dealing with tool version conflicts may be a thing of the past.

Make sure you’re using the latest version of Visual Studio.

Bugs are fixed all the time, especially with Xamarin. Make sure you’re running the latest bits and your problems may be solved.

Experiment with Hyper-V Enabled and Disabled.

I’ve generally had issues with virtualization when Hyper-V is enabled. If you’re having trouble with it enabled, try with it disabled.

To enable/disable Hyper-V, go to Start, then type Windows Features. Choose Turn Windows Features On or Off. When the selection list comes up, toggle the Hyper-V feature accordingly.

Note: You may need to disable Windows Device Guard before you can disable Hyper-V. Thanks to Matt Soucoup for this tip.

Use a real device.

As a mobile developer, you should never trust the emulators to reflect the real thing. If you can’t get the emulators to work, and even if you can, you have the option of picking up an Android phone or tablet for cheap. Get one and test with it. If you’re not clear on how to set up Developer Mode on Android devices, it’s pretty simple. Check out Google’s article on the subject.

Try Xamarin’s HAXM and emulator troubleshooting guide.

The Xamarin folks have a guide, too.

If all else fails, use the ARM processors.

This is your last resort. If you don’t have an Intel processor, or a real device available, use the ARM processors. They’re insanely slow. I’ve heard there’s an x86 emulator from AMD, yet it’s supposedly only available for Linux. Not sure why that decision was made, but moving on… 🙂

Have another solution?

Have a suggestion, solution, or feature I’ve left out? Let me know and I’ll update!

 

My latest Visual Studio extension is now available! Get it here: 2017, 2015

So what is CodeLink?

Getting two developers on the same page over chat can be time consuming. I work remote, so I can’t just walk to someone’s desk. I often find myself saying “go to this file” and “ok, now find function <name>”. Then I wait. Most of the time it’s only 10-20 seconds lost. If it’s a common filename or function, it takes longer. Even then, mistakes can be made.

So I asked myself: Self, wouldn’t it be great if I could send them a link to the place / cursor location in the solution I’m at? Just like a web link?

CodeLink was born.

So here’s what a CodeLink looks like:

codelink://[visualstudio]/[AurisIdeas.Common.Security\AurisIdeas.Common.Security.csproj]/[ParameterFactory.cs]/[9]

I would simply share that CodeLink with a fellow developer. They’d select “Open CodeLink…” in VisualStudio, paste it in, and be brought to that line of code in that project. No more walking them through it, much less waiting.

Technically, the format is:

codelink://[Platform]/[Project Unique Path]/[File Unique Path]/[LineNumber]

What’s it good for?

Other than what I’ve suggested, and what you come up with, I’m thinking CodeLink will help you, teams, teachers, and students with:

  • Include CodeLinks in bugs, code reviews to highlight what needs to be reviewed
  • Share CodeLinks on Git repos, pointing to specific code examples, points of interest, and so forth
  • Share CodeLinks with students so they can continue referring / reviewing useful code

So what’s next?

When I was thinking of the link format, I figured I may end up extending this to VS Code and other editors in the future. After all, not everyone uses VS. Why not XCode, Visual Studio Mac, Atom? So, I added a type identifier.

As always, I look forward to your feedback. Hit me up on Twitter or LinkedIn.

 

Want to learn all about Xamarin and how you can use it, while not spending most of your time watching code scroll by in a video? I figured there was room for an explainer without being a close-captioner for a code tutorial. Enjoy my latest video!

https://www.youtube.com/edit?video_id=AhvofyQCrhw

From the description, along with links:

Have you been considering Xamarin for your cross-platform mobile app? This presentation will help.

In this non-code-heavy presentation, we’ll discuss:

* What is Xamarin
* Development Environment Gotchas
* Creating a Sample To Do List App without writing any code
* Reviewing a real Xamarin app that’s “in the wild”
* Review native, platform-specific integrations
* Discuss gotchas when using Xamarin, and mobile apps in general
* Answer audience questions

Why not code-heavy? Because there are many examples you can follow online. This presentation will provide valuable information you can consider while reviewing the myriad of tutorials available to you with a simple Bing or Google search, or visiting Pluralsight, Microsoft Virtual Academy, or Xamarin University.

If you have any feedback, please leave in the comments, or ask me on Twitter: @Auri

Here are the links relevant for this presentation:

Slides: https://1drv.ms/p/s!AmKBMqPeeM_1-Zd7Y…

Indy.Code Slides with Cost and Performance Figures: https://1drv.ms/p/s!AmKBMqPeeM_1-JZR4…
(you can find the Indy.Code() presentation on my YouTube channel)

Google Xamarin vs. Native iOS with Swift/Objective C vs. Android with Java Performance Article: https://medium.com/@harrycheung/mobil…

Example code for push notifications, OAuth Twitter/Facebook/Google authentication, and more: https://github.com/codemillmatt/confe…

Link to Microsoft Dev Essentials for $30/month free Azure credit and free Xamarin training: https://aka.ms/devessentials

Microsoft Virtual Academy Multi-Threading Series: https://mva.microsoft.com/en-us/train…