How to create a simple app from C++ source code - android

I have written a very basic program in C++. It only interacts with the user via text from the console.
How can I turn this into an app for my android phone? I just want to do the exact same thing, interact via boring text in a black screen (no graphs, no fancy interface, no nothing)
Is there a simple way to achieve that? I was told that I should translate my program into Java, and then go from there; is that the only way, or better, the simplest way?

As far as I know, you will need a Java UI even for "boring text in a black screen". (The project https://github.com/jraska/Console looks like it might help with that. But note I haven't used it, can't vouch for how it works, and might be mistaken about what it does.)
But you probably don't need to translate absolutely all your C++ code to Java. The official Android Developer page https://developer.android.com/studio/projects/add-native-code describes how to include C++ code into an Android app, using the Java Native Interface (JNI). You will need to provide interface functions using JNI so that the Java code can call the C++ functions. And you may need to generalize how your C++ code handles input and output, e.g. to use streams or strings instead of std::cin and std::cout directly.

Related

Are there any simple way to use c/c++ source code directly on my android application?

I am currently working on an android application that evaluate images in different aspects, and I found that there are lots great open source algorithms can be used.
Problem 1: Most of the algorithms are designed on c/c++/matlab languages that cannot be applied directly.
I've search that NDK is a tool that allows us develop android application by other languages, but the setup procedures are quite complicated that I stuck for days. So before I go further on it, I would like to first ask whether I can include other's c/c++ source code directly like calling java library?
Problem 2: For example, I would like to use Point Matching algorithm's source code in my application, but there are lots files inside as it's just source code but not library/plugin. What are the steps to apply the require functions in my android application?
(the most desired way is to blindly input some images to the alogrithm, and it returns the results like calling functions, which I dont have to understand the working principle of it.)
You can't directly use other C++ libraries, you have to build them for Android first using NDK. If there is a version of the library built for Android, then, of course you can use it directly by linking to it using NDK.
You have two options here. First, you create a regular Java application for Android, write a C++ wrapper for handling calls to native side and build the necessary source files using NDK. Your java application will make calls to wrapper using JNI and the wrapper will call your actual C++ functions as in Java->JNI wrapper on C++->Your actual C++ source.
Second option is going fully native, which will leave out Java, JNI calls and the wrapper. You can access your source files directly as if you were writing a desktop C++ application. In the end you will have to build using NDK but this step is required in any case.
As a suggestion, you can also take a look at OpenCV for image processing purposes. It has libraries built for Android, all you will have to do is to link them.
Short version.
Download opencv4android library. Import it in eclipse and see if everything is fine (compile errors, output, etc.).
Secondly, try to import face detection application and try to understand how it works.
It has a java part and a native part.
In order to understand how it works you must understand how java interacts with C++, more or less how NDK works.
One important aspect is to learn how to create your interfaces in C++, based on the native ones defined in java. When you got there then you can try creating your own application.
After that you can come here and ask specific questions.

Native Activity vs SDK Activity in terms of U.I

I've been doing a fair amount of research, and have even experimented some with the NDK for Android (not so much the SDK). What I haven't been able to really find though is a clear and concise definition for what the NDK cannot do (besides lack of exception handling and rtti).
I've been mapping out some code for a game and a game engine for Android (Written entirely in the NDK) but it seems to not be as supported as many would like it to be. Not only that, but I'd like to be able to give my game a sexy U.I. without having to write everything from scratch in OpenGL.
While I'm sure it's easier in Java, I'd like to know if the NDK's front end/U.I. components are getting to a point to where they'd even be comparable with Java in terms of Touchscreen IO , Sound, and Graphical Interfaces. Worst case scenario I can write the U.I. in Java and just call native methods from that, but I'd like to be able to do more if possible.
Thanks.
Edit
If C++ is even somewhat on par with Java's U.I. feature set, it would be cool to know which of the two gives more control and customization. For example, while the Java implementation may be easier to use, does it give the programmer a lot of options to fine tune a "look" which resembles something specific?
Official NDK can do exceptions and rtti just fine. Read the "docs/CPLUSPLUS-SUPPORT.html" file distributed with Android NDK.
In C++ only thing you can not do is implement Java interface, inherit Java class and define new Java class. Otherwise - you can do everthing Java can. Only problem with that will be that a lot of things (like accessing Java object members, or calling Java functions) will require usage of JNI and that code will look really ugly. So if you need for UI creating/inheritance of Java classes, then you can code everything in C++.
I suggest to use JNI only for performance critical code. Mixing code - Java for UI, mathematical calculations in C/C++ is really easy.
Or if you code game by using OpenGL ES - that's also fine.

What is the best way to add "Tweet" button to a C++ application for Android

I want to add a "Tweet" button to a C++ application without use of heavy libraries and frameworks. The application is portable and runs on Android and Windows.
I am not sure if I understand your setup. If you have implemented a native part of an Android app you can still write some java UI code and call your c++ code from there.
If you want to have a full portable solution though I would render simple button with help of OpenGL.
UPDATE Oh I see what you meant, so this is actually quite simple. For Android many people use Twitter4j which is not that "heavy". You can also implement API calls on your own, see the official docs. Besides, there are a couple of more possibilities on SO with links to some tutorials.
As for portability, it gets a bit trickier. I would stick with twitter API and implement HTTP calls directly. The quickest way to get it done in a portable way is to write a thin wrapper around the socket calls as someone here suggested.
You could also use Boost.Asio or cURL library, but I have not checked them personally. The latter is available for windows and has recently been ported to Android.
Hope that helps!

100% Native C Application on Android?

Is there anyway I could write 100% native C code for Android? I know there are ways to write some C code inside Java code, but I don't know any Java and I hate Java anyway.
Is there anyway I could write pure C code that will run under Android?
There is, as of Android 2.3: NativeActivity. But you don't get access to any of the niceties of Android's Java libraries; you're on your own in the wild west. This is really intended for people writing high-performance games.
Yes, there is support for writing completely native activities. You can check out the native-activity sample application.
I would not recommend this path, though, as in my experience applications that are heavy in NDK code are very difficult to debug. I would rate the Android native debugging experience as lacking.
Edit - one caveat is that you will still be doing plently of Java--just through the JNI.
Might be more trouble than it's worth, you could possibly write your logic in C code and import that to java using extern or external (I forget which now) and then do the GUI in java. There's really no point to using straight C in android unless you want to REALLY optimized your logic. Most of the calls you can make are wrapped anyways so you would have to make those calls to access certain things on an android device. Long story short : not a good idea unless you need faster logic.
You can write most of the application in C around a NativeActivity. However, some Android features can only be used from Java, so you'll need to use JNI instead of pure native. See the official overview.

Android NativeActivity

The Android NDK has just been significantly expanded to include support for writing android applications entirely in native C/C++ code. One can now capture input events on the keyboard and touch screen using native code, and also implement the application lifecycle in C/C++ using the new NativeActivity class.
Given all the expanded native capabilities, would it be worthwhile to completely bypass Java and write Android application in native code?
The NDK is not native per-se. It is to a large extent a JNI wrapper around the Android SDK. Using NativeActivity gives you a convenient way of dealing with certain app-life cycle events, and add your own native code on top. ALooper, AInputQueue etc. are all JNI wrappers of the Java SDK counterparts, some with additional code that is private and unaccessible for real apps.
When it comes to Android development, there's no such thing as writing an application entirely in native C++ - you will (in every real App case that I can think of) always need to use the Android API:s, which are to a huge extent pure Java. Wether you use these through wrappers provided by the NDK or wrappers that you create yourself doesn't really change this.
So, to answer your question: No, it wouldn't be worthwhile, because you would end up writing JNI wrappers for SDK calls instead of writing JNI wrappers to your own Java methods that do the same thing, with less code, simpler code and faster code. For example, showing a dialog using "pure c++", involves quite many JNI calls. Just calling a Java method through JNI that does the same thing will give you faster code (one JNI call), and, arguably, code that is easier to maintain.
To fully understand what you can do, you really must examine the Android source code. Start with native_app_glue.c, which is available in the NDK, then continue with the OS implementation of AActivity, ALooper, AInputQueue etc. Google Code Search is a great help in this. :-)
If it is easy to do in Java, and includes many calls, call a method through JNI that does it all, rather than writing all the extra code to do it with multiple JNI calls. Preserve as much of your existing C++ code as is reasonable.
Not if you are just making a standard application. The Java SDK is more complete than its Native counterpart right now so you would still be making things more difficult for yourself.
If you are not doing something that requires the NDK (read: real time performance sensitive) then stick with Java.
Just some food for thought but if you have an app on iOS and Android, some C/C++ code might be shareable. Obviously the iOS Obj-C and platform specific code wouldn't work elsewhere. (Ditto for the Android specific stuff). But you might be able have some shared code that's platform neutral.
If you can, stick with the java style apps until versions of Android supporting native activities constitute a significant fraction of the installed base.
For things that were hard to do before - particularly ports of existing code - this will probably be a big help.
It's not entirely clear yet what has changed vs. just writing your own thin java wrapper. For example, is there still a copy of the dalvik VM hanging around?

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