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);
}

I recently read a “Coding Question” thread, and a developer was asking what we all thought about this article. I wanted to hold on to my replies, so I’m posting it here for posterity 🙂

Auri:

Only a Sith deals in absolutes. There are use cases for everything, with exceptions.

Auri:

Seriously, though, I’d write tests to ensure the states that you want work as expected.

Auri:

And now that I’ve had my coffee:

Exceptions are a necessary construct. If something doesn’t go as planned, we need a way to handle it. In his article, he’s against blindly swallowing exceptions. That’s generally sound advice. Ask yourself: “Is this an expected exception? If so, do I have a specific exception handler for it, or am I just using the generic catch-all? Have other exceptions occurred? If so, is this one expected? Didn’t I read about C# support for exception switch statements? Did I just shiver?”

Like I was explaining before, only a Sith deals in absolutes. The way I see it, if an error is unexpected, I should have specific use cases for how to handle that exception. I should, generally, never blindly swallow with no logging, or simply re-throw and assume the code above will address. At least, not without a custom/known/non-generic exception I can check up the chain, or include in an integration test. Good article about testing [written by a friend] here, btw: https://arktronic.com/weblog/2015-11-01/automated-software-testing-part-1-reasoning/
At the very least, and I try to follow this rule as much as possible, LOG in any exception for tracking and pro-active/offensive development. Better that you can read logs, or run scripts to let you know about exceptions, and help things go right, than to be blind with a “well, the code seems to work, so let it be” approach. That’s the key goal, really: Help things go right. There are exceptions [heh] to this rule, like simple utility apps whose job is to bulk process data, and exceptions are part of the game. Still, I try to make sure to log, even with those. Unexpected/unintended bugs tend to appear when you’re dealing with massive amounts of data, and logs give a perspective you can’t see from debugging.
Ok, next cup of coffee.

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!

 

CEATEC, the Combined Electronics and Technology exhibition in Makuhari, Japan is this week. The latest innovations from Japanese companies are showcased here, often many months before Americans get a taste. I’ll be posting a reporter’s notebook in a bit. For now, enjoy clicking through videos and photos of cool things found on the show floor!

Panasonic’s Cocotto Children’s Companion Robot

Bowing Vision Violin Improvement Sensors & App

Hitachi Robot for the Elderly, and those with Dimentia

Omron “Ping Pong” Robot, Now with “Smash” Shot Abilities

au’s AR Climbing Wall

Unisys’ Manufacturing Robot That Follows Lines

VR Racer

Takara Tomy Programmable Robot

Dry Ice Locomotion

Airline Customer Service Bot Attendant

Feel the Biker’s Heartbeat

Wind Sensors Paired with Fun Animations

The Trouble with Tribbles – Qoobo Robot

Spider-Like Robot from Bandai

Semi-Transparent Display with Water Effect

Bandai BN Bot

Model Train

Kunshan Plasma

The Many Faces of Robots at CEATEC

There were MANY robots at CEATEC. Many just sit there and answer basic questions. Still, some, like Omron’s Ping Pong robot, can learn and adapt and make a difference.