Develop Reference

Xamarin iOS Crash on Android

We are use Xamarin forms local notifications on our app. with the below line in the code it causes the app the crash
UNUserNotificationCenter.Current.RemovePendingNotificationRequests(requests);
even tho the line should only be run on iOS devices. this is done with the following;
`
if (Device.RuntimePlatform == "Android")
{
}
else
{
UNUserNotificationCenter.Current.RemovePendingNotificationRequests(requests);
}
`
the below error is given with the UNUserNotificationsCenter in the code
System.IO.FileNotFoundException: Could not load file or assembly 'Xamarin.iOS, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065' or one of its dependencies.
anyone any ideas??
We have tried completely reimplementing the local notifications, clean and clearing bin/obj. updated both machine and vs to the latest version, updated frameworks.
built on VS Mac 2022 17.3.6
android framework 13.0.0.0

Android h3: A Hexagonal Hierarchical Geospatial Indexing System

I want to integrate h3 java binding library to my android app and I'm getting following exception:
java.lang.UnsatisfiedLinkError: No native resource found at /android-armv7l/libh3-java.so
at com.uber.h3core.H3CoreLoader.copyResource(H3CoreLoader.java:67)
Does anyone used this library before for Android OS?
Thank you.

Initially, following the intended usage as seen in their README should make it work. If it doesn't, see below.
Known Issue: Android, can't use library
UnsatisfiedLinkError: This can be encountered when the corresponding native library is not copied/detected in the project. Following NickRadu's workaround should make it work.
Below is a step-by-step guide.
Add a JNI folder in your project app folder and rename it jniLibs (app/src/main/jniLibs) (for some reason, having it named jni only doesn't work for me).
Get the H3 JAR (make sure you use the same version) and extract the JAR contents.
Copy the folders prefixed with android- and insert them in the jniLibs folder (from step 1).
Rename the copied folders, remove the android- prefix.
Add splits { abi { enable false } } to your app's build.gradle file (within android).
Done. In general, the library should now work as expected.
If during the app installation you encounter:
INSTALL_FAILED_NO_MATCHING_ABIS,
then depending on your test device, create a copy of the folder (along with its contents) and rename it as needed.
For example, a device running on arm64-v8a, I just made a copy of the arm64 folder and renamed it to arm64-v8a. Or if you're using an emulator, make sure that you're not using one with an x86 CPU.
D8 errors: Invoke-customs are only supported starting with Android O (--min-api 26), add these compile options in your app's build.gradle (within android -- note that it may change depending on your system's Java version)
compileOptions {
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}
Note: It is best to test the app on multiple CPU architecture types first to see it's behavior.
To quickly see the CPU Architecture of the device, you could install Droid Hardware Info, or run a quick test code yourself.
Here's a test block I used and its corresponding result logs:
private fun testH3() {
val h3 = H3Core.newSystemInstance()
val lat = 37.775938728915946
val lng = -122.41795063018799
val resolution = 8
val hexAddr = h3.geoToH3Address(lat, lng, resolution)
val hex = h3.stringToH3(hexAddr)
val kRingsResult = h3.kRings(hexAddr, 1)
Log.d("H3Test", "geoToH3Address: $hexAddr")
Log.d("H3Test", "stringToH3: $hex")
Log.d("H3Test", "kRings: $kRingsResult")
}
Result:
D/H3Test: geoToH3Address: 8828308281fffff
D/H3Test: stringToH3: 613196570331971583
D/H3Test: kRings: [[8828308281fffff], [8828308281fffff, 882830828dfffff, 8828308285fffff, 8828308287fffff, 8828308283fffff, 882830828bfffff, 8828308289fffff]]
I made a sample project where the library works as expected. See android-uber-h3-sample.

Also be advised that the library will not work on Android api < 26 without some modifications to the code. The function that H3Core relies on to parse the hex long to hex string Long.parseUnsignedInt was not added to Android Java until api 26.

App crashes on Launch when made as system application

I developed an application that uses DJI SDK. When installed as an system application it crashes on Launch because its not able to load the libraries. It works fine when installed as normal application.
Steps followed to make system application
1)Rooted the device
2)Copied the .apk file to system/app directory
3)Rebooted the device
4)App was installed as default application but crashed on Launch
After commenting out the following line related to DJI SDK and followed the same steps as above. It worked fine as system app.
Helper.install(context);
The implementation of Helper class which is in DJI SDK is as below:
public static void install(Application app) {
Object var1 = null;
try {
System.loadLibrary("DexHelper_sdk");
if (PPATH != null) {
System.load(PPATH);
}
} catch (Error var3) {
;
}
String app_dataDir = app.getApplicationInfo().dataDir;
DexInstall.install(app, new File(app_dataDir + "/.cache_sdk/sdkclasses.jar"));
}
As far as my understanding the crash is because the system is failing to load the libraries.
My gradle looks similar as in the following link:
https://github.com/dji-sdk/Mobile-SDK-Android/blob/master/Sample%20Code/app/build.gradle

this issue has been fixed since 4.6 version of Android MSDK, pls try to update to the later version, right now the 4.7.1 has been released.

Xamarin Forms fails to create an instance of DI container

Using Visual Studio 2017.
Created the default Xamarin Forms project (.net standard 2.0 + android). No changes in project configuration, Debug mode.
Compile -> Build -> Success (simple page with a standard text).
Added Unity/Autofac and created an instance of the container in App.
In Unity:
Object reference not set to an instance of an object
Similar in AutoFac
p.s. tried the approach to skip linking assembly System.Core
upd.1
This is absolutely standard solution with the only 1 line of code:
public App ()
{
InitializeComponent();
var c = new UnityContainer(); //this is the line for Unity
MainPage = new App2.MainPage();
}
The scenario with Autofac is similar. But it fails on RegisterType with exception Target of Add is null (NullReferenceException)
upd.2
This fails both in Release and Debug mode
This does not fail in simulator!
This fails during any kind of execution on phone directly (inculding Xamarin Live)

Build an android apk from Unity3d project working with C/C++ dll

I made a Unity3d project working with C/C++ Dll.
So first I made the dll in Visual studio.
// mydll.cpp
#define EXPORT_API __declspec(dllexport)
extern "C" {
int EXPORT_API add(int a, int b)
{
return a+b;
}
}
And I added this dll into my Unity3D project and called
// C# script in Unity3D
public class TestDll : MonoBehaviour {
[DllImport("mydll")]
private static extern int add (int a, int b);
void Start() {
int a = add (100, 200);
}
}
This code works well and I got the correct result in Unity3D editor.
So I built this project to android platform and got an apk.
I installed and run this apk on my android device but the app doesn't work.
The app didn't run the Dll function.
Whats the matter? I tried to find out the solution in Google and here, but didn't get anything, yet.
Please help me.
Thanks.

Your dll must be in Plugins folder for Windows, it can work for Editor too. for Android you must replace in Plugins/Android folder. Build and write me ok

LearnCocos2D's comment is accurate.
To get Unity to DllImport() a shared library on Android, you must use an NDK compiler and specify a compile config for your target Android platform. Moreover, Unity requires you to specify the architecture of the Android platform in the build settings, eg.. "arm v7" vs "arm64".
As an aside, in Unity 2019.4 - selecting "Load on Startup" in the inspector page of my .so elicits a "DLLNotFoundException".
Overview of this: https://docs.unity3d.com/2019.4/Documentation/Manual/AndroidNativePlugins.html
NDK's CMake guide for getting you started on compiling correctly: https://developer.android.com/ndk/guides/cmake