Develop Reference

Visual Studio can't find extension methods Splat.BitmapMixins.FromNative() and Splat.BitmapMixins.ToNative() in Android app

While upgrading a Xamarin app that leverages Splat's bitmap functionality we are getting errors around the use of the methods mentioned in the title:
'IBitmap' does not contain a definition for 'ToNative' and no accessible extension method 'ToNative' accepting a first argument of type 'IBitmap' could be found (are you missing a using directive or an assembly reference?)
In an effort to troubleshoot the problem we have created a new sample Android-only Xamarin app and referenced Splat and Splat.Drawing via NuGet. We then added calls to these methods and have reproduced the error:
public void Bar(IBitmap source)
{
Bitmap native = source.ToNative();
IBitmap bitmap = native.FromNative();
}
It seems as though the Andriod app may not be referencing the proper build of the Splat libraries. When I monitor paths containing %USERPROFILE%\.nuget\packages\splat in ProcMon I don't see any attempt by Visual Studio to open/read anything other than files in the .\netstandard2.0 directories during the build process.
When I open the netstandard2.0 libraries in DotPeek I can see that the class BitmapMixins is not included, but it is included in the monoandroid90 builds.
How do I get the reference to Splat in the Android project to pull in the proper build of Splat?
Example project can be found here: https://github.com/jctlp/SplatBitmap

The error caused by that you did not have the extension methods to assist with dealing with Bitmaps of ToNative and FromNative.
Please do not add reference by installing the Splat from NuGet directly. Add reference to the whole project of Splat would be okay.
Download the whole Splat project from the link below.
https://github.com/reactiveui/splat.git
I create a Xamarin.forms app named App1. And create a class Class2.cs in App1.Android. When I add reference to Splat from the project. It works well with ToNative and FromNative extension method.
Please note: Do not use the Bitmap, use Android.Graphics.Drawables.Drawable or var instead.
public void Bar(IBitmap source)
{
Android.Graphics.Drawables.Drawable native = source.ToNative();//var
IBitmap bitmap = native.FromNative();
}

How to resolve "Obsolete custom lint check" for my custom IssueRegistry written in Kotlin and make it work (Android)

I am trying to implement custom lint checks (using Kotlin). I have set up a module for my custom checks and added classes to test my first lew lint check, mostly following these two tutorials here and here.
So I now have a module, I have a custom IssueRegistry, I've created an issue and a Detector class for it. So far it seems complete. I've added a test to check if my lint check works and it looks alright.
I have added my module to the project by referencing it in settings.gradle like this: include ':app', ':somemodule', ':mylintmodule'
Now if I run the linter using ./gradlew lint I get a lint result file telling me this:
Lint found an issue registry (com.myproject.mylintmodule) which requires a newer API level. That means that the custom lint checks are intended for a newer lint version; please upgrade
Lint can be extended with "custom checks": additional checks implemented by developers and libraries to for example enforce specific API usages required by a library or a company coding style guideline.
The Lint APIs are not yet stable, so these checks may either cause a performance degradation, or stop working, or provide wrong results.
This warning flags custom lint checks that are found to be using obsolete APIs and will need to be updated to run in the current lint environment.
It may also flag issues found to be using a newer version of the API, meaning that you need to use a newer version of lint (or Android Studio or Gradle plugin etc) to work with these checks.
To suppress this error, use the issue id "ObsoleteLintCustomCheck" as explained in the Suppressing Warnings and Errors section.
So it tells me that I am using a newer API verion in my custom lint check, right? This is my custom IssueRegistry (minus some parts not relevant for this problem):
class MyCustomIssueRegistry : IssueRegistry() {
override val issues: List<Issue>
get() = listOf(ISSUE_NAMING_PATTERN)
override val api: Int = com.android.tools.lint.detector.api.CURRENT_API
override val minApi: Int = 1
}
From googling this problem and finding this issue I figured I have to override and set the right API version (and maybe the min API?) by overriding these properties like I did above (this version is my last attempt, directly taken from that issue).
So this property can be set to values between -1 and 5, meaning this (taken right out of the lint.detector.api class):
/** Describes the given API level */
fun describeApi(api: Int): String {
return when (api) {
5 -> "3.5+" // 3.5.0-alpha07
4 -> "3.4" // 3.4.0-alpha03
3 -> "3.3" // 3.3.0-alpha12
2 -> "3.2" // 3.2.0-alpha07
1 -> "3.1" // Initial; 3.1.0-alpha4
0 -> "3.0 and older"
-1 -> "Not specified"
else -> "Future: $api"
}
I have tried all of them, plus the one above adding a minApi override too, and I keep getting the exact same result for each of them.
Also I am unable to locate what other API version this is compared with. Is there a place where this is set for the regular linter in an Android project?
It's also unclear to me what I have to do to make sure my changes got applied - is it enough to change some code, then run lint, or do I have to compile the project first, or build & clean?
Following the tutorials, I added my custom lint check by adding this to the app's build.gradle: lintChecks project(":mylintmodule")
Is that even right? The API issue on my registry class shows up no matter if my lint check is referenced (and hopefully used) like that or not. I have also tried the other method described in the first tutorial, adding this task to the linter module build.gradle:
defaultTasks 'assemble'
task copyLintJar(type: Copy) {
description = 'Copies the lint jar file into the {user.home}/.android/lint folder.'
from('build/libs/')
into(System.getProperty("user.home") + '/.android/lint')
include("*.jar")
}
// Runs the copyLintJar task after build has completed.
build.finalizedBy(copyLintJar)
But since I can't figure out how to see if my custom checks are actually run, I don't know if that works as intended either.
So how do I get this warning resolved (since I interpret the text as "As long as the versions don't match I will not try to run your lint check"), and how can I make sure my lint check is actually run by the linter?

Why an unresolved reference on attempting to access constant values?

The app defines constants in a Kotlin singleton object:
#file:JvmName("APIConstants")
package com.myapp.api
object APIConstants {
const val HTTP_RESPONSE_CODE_NOT_AUTHORIZED = 401
etc....
}
They are then used in another class:
import com.myapp.api.APIConstants.HTTP_RESPONSE_CODE_NOT_AUTHORIZED
etc ...
class API {
private fun returnBadResponse(response: Response<*>, callback: ApiAuthListener<*>) {
if (response.code() == HTTP_RESPONSE_CODE_NOT_AUTHORIZED) {
callback.onBadAuthToken()
} else {
callback.onFailure(response.message(), getServerError(response))
}
}
In this class Android Studio (3.0 beta) provided a hint to add the import for the constant, and it does not give any indication of a problem (no red underlines etc, and the constant reference in the method is shown in purple italic text indicating it has been resolved) but when I build the project I get this:
Error: Unresolved reference: HTTP_RESPONSE_CODE_NOT_AUTHORIZED
I've tried clearing the IDE cache and restarting it, and doing a clean build, which make no difference. I've tried removing the #JvmName annotation and even placing the const values in the root of the file with no containing object but neither allows a build.
Why is the class failing to reference the constant, especially when the IDE strongly suggests it can resolve it?

And the solution is.... to make very sure all Kotlin source files have a .kt file extension! In this case the APIConstants file was called "APIConstants" and not "APIConstants.kt" which appears to mean the IDE was able to resolve references based on the content of the file, but the build tools could not. Confusingly Android Studio showed a Kotlin K icon on the filename despite the lack of a .kt extension.

Xamarin Realm no realmobject has linker stripped them

I am receiving an exception at runtime as follows.
"No realmobject. Has linker stripped them...."
My solution includes a PCL, Android and IOS project with Visual studio Mac and the realm package 1.6.0 installed in each project. I've also checked that Fodyweaver.xml includes the correct reference and all packages have th same version.
When I have the PCL included in the same folder as the solution (i.e like the default multiplatform solution with PCL) everything works ok.
However I moved the PCL project which includes all the realm logic to a separate folder so I can use it across multiple solutions. My solution now includes the PCL from this external folder and the iOS and Android project also reference the realm packages. the app compiles fine but when I run the application it now receives this exception on the first call to use realm.getinstance.
If Input the PCL project back into the same folder as the main solution as originally created it works fine.
can anyone advise a fix for this ?

I've solved the issue now. Firstly I had applied the solution from #sushhangover, but it didn't work straight off.
After some investigation I discovered the compiler was not weaving the classes and realm objects into the library at all.
I simply loaded the library independently of my main solution, removed and reloaded realm packages and Fody, cleaned it all, rebuild All. and then I could see the fodyweaver working properly. I then added the reference back into my main solution and it all works .

This is the same issue I have when placing my RealmObject models into a separate library (PCL or NetStd) as I use a Viper architecture and I share the same model across multiple solutions.
When Realms.Realm.GetInstance(....) is called the Realm initialization assumes the RealmObjects will be in the same assembly or that the assembly containing is already loaded, but they are not in this case. You can tell this is the case as a compiler warning is issued in the assembly build (via the Fody processing) that is calling GetInstance but that does not have any RealmObjects in it:
Warning: Fody/RealmWeaver: Default schema appears to be empty. This is not an error if you don't have any RealmObject inheritors declared. Otherwise it may be a bug with the weaver. (GeneticCancerSelectors)
So I add a static class to my Realm model library:
public static class RealmModel
{
public static Realms.Realm GetInstance() => GetInstance("");
public static Realms.Realm GetInstance(string databasePath) => GetInstance(new RealmConfiguration(databasePath));
public static Realms.Realm GetInstance(RealmConfigurationBase config = null) => Realms.Realm.GetInstance(config);
public static Task<Realms.Realm> GetInstanceAsync(RealmConfigurationBase config) => Realms.Realm.GetInstanceAsync(config);
}
Now when you need to get a Realm instance, do not call:
Realms.Realm.GetInstance()
But call the one in your Model assembly:
RealmModel.GetInstance()

Thanks to Chris Baxter.
That's my situation.
[WPF Application, Fody 3.0.3, Realm 3.4.0]
Exception: No RealmObjects. Has linker stripped them?
...This is my First Time using Realm, and It's really bad feeling...
A [Brand New] Blank WPF Project
Nuget => Realm
Required FodyWeavers.xml file Created in Solution Folder, because Nuget can't
do this for you now.
(Somehow I Update Then Downgrade a latest version of Fody, after
recongized that Realm don't support Any Fody which version newer
than 3.X)
Awful Exception Occurs, ooooops!
(hours work with System
Auth, SpecialFolder, etc... Until I Discovered Chris Baxter's
answer)
Xml file content:
<?xml version="1.0" encoding="utf-8" ?>
<Weavers>
<RealmWeaver/>
</Weavers>
How to Solve the Problem:
Just Clean And ReBuild Solution, Problem Solved.

Getting the Android SDK directory within a gradle task

Recently the gradle plugin for android got updated (with android studio), after which the previous way of getting to the SDK directory ceased to work. The expression
${android.plugin.sdkDirectory}
which worked in an older version now returns the error
Error:(42, 0) No such property: sdkDirectory for class: com.android.build.gradle.LibraryPlugin
What would be the proper way of getting the android SDK directory being used, preferably independent of the user's configuration such as plugin and gradle version? The script needs to be shareable with several users.

Since all the previous answers depend on the environment or specific user intervention on top of normal configuration, I'll just post my technically messy fix.
if (android.hasProperty('plugin')) {
if (android.plugin.hasProperty('sdkHandler')) {
androidPath = android.plugin.sdkHandler.sdkFolder
} else {
androidPath = android.plugin.sdkDirectory
}
} else {
androidPath = android.sdkDirectory
}
Unlike all previous methods, this actually works, but it still looks hacky.

In gradle.properties set location sdkdir=/home/user/android-sdk and then in gradle you can use $sdkdir

I'm using Android gradle plugin v1.2.3 and this works fine:
${android.sdkDirectory}

You can use
$System.env.ANDROID_HOME

export ANDROID_HOME=/xxx/xxx/ in shell, then use it by System.env.ANDROID_HOME in gradle file.