Develop Reference

Read value returned in CompletableFuture

A function from some SDK is returning me a CompletableFuture. How can I read the value properly once it's reached.
My Code:
CompletableFuture<Web3ClientVersion> web3clientCompletableFuture;
web3clientCompletableFuture = web3jNode.web3ClientVersion().sendAsync();
sendAsync() Code (In SDK):
public CompletableFuture<T> sendAsync() {
return web3jService.sendAsync(this, responseType);
}
I can access the returned data using get(), but that would make the whole process syncronus and block UI.
I've checked the functions signatures on Android API Reference, like:
thenApply(Function<? super T, ? extends U> fn)
handle(BiFunction<? super T, Throwable, ? extends U> fn)
But seems I require some code examples.
[Note: I'm not so familiar with lambda]

Here is a tutorial that has examples that show you how to use these powerful methods of CompletableFuture. You are right you want to use thenApply() if you have to return value after you process the future. But if you simply want to process the future and not return anything, you should use thenAccept() and thenRun(). There are other methods listed with examples as well.
Here is an example that simply returns a CompletableFuture of type integer:
CompletableFuture<Integer> mynumber = null;
if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.N) {
mynumber = CompletableFuture.supplyAsync(() -> {
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
throw new IllegalStateException(e);
}
return 4 * 4;
});
}
Here arg is the result(CompletableFuture) from the above step, and in your case the data you are receiving from the SDK. You are attaching a callback method(thenApply()) and do what ever you would like to do with it. Depending on your implementation, you can attach multiple thenApply(). Here I am calling a method that will take the result and do some computation with it.
CompletableFuture<Integer> willdoStuff = null;
if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.N) {
willdoStuff = mynumber.thenApply(arg -> {
compute(arg);
return arg / 2;
});
}
public void compute(int someInt){
Toast.makeText(getApplicationContext(), "The result of the computation is" + someInt, Toast.LENGTH_LONG).show();
}
Just comment out the sleep code to execute this code in the main thread.
The Lambda function is simply input and output, the arguments before {} being the input and the statement within the {}, which is actually a function that does something with the arguments(input). You might want to ask different question in regards to that.

How can I pass data to libcore on Android?

I was modifying the libcore on Andorid for debugging purpose.
It took a lot of time to build even for a variable change.
Is it possible to pass the data to libcore of android?
(so I can change the data in the running time).
I tried System.getProperty() but the data could not cross process.
I also tried SystemProperties.get() but it seems it can not be used in libcore (it could not find the package and symbol).
Does anyone know how to pass data to the libcore on Android?

Thanks Nativ.
JNI is doable but a little complicated for me.
Finally, I used a simple, easy but stupid way to do that.
I created a file and saved my parameter in this file, and get the data from libcore.
It is a stupid way but worked for me for debugging.
Now I don't need to rebuild libcore and It saved much for me.

You can use reflection on class android.os.SystemProperties to get System Properties at runtime.
Code example:
public static String getSystemProperty(String key) {
String value = "";
try {
Class clazz = Class.forName("android.os.SystemProperties");
if (clazz != null) {
Object object = clazz.newInstance();
value = (String) (clazz.getMethod("get", String.class).invoke(object, key));
} else {
System.err.println(TAG + ", getSystemProperty: Class is null.");
}
} catch (Exception e) {
e.printStackTrace();
}
return value;
}

Getting ProtoBuf.ProtoException using OsmSharp in Xamarin Android

I am trying to test a sample project called Android.Routing.Offline from OsmSharp.Samples in Github.
After two taps on the screen (the first one gets just the GeoCoordinate) I get a ProtoBuf.ProtoException in the Router.cs
private static IBasicRouterDataSource<CHEdgeData> _graph;
public static void Initialize()
{
var routingSerializer = new CHEdgeDataDataSourceSerializer();
_graph = routingSerializer.Deserialize(
Assembly.GetExecutingAssembly().GetManifestResourceStream(#"Android.Routing.Offline.kempen-big.contracted.mobile.routing"));
}
public static Route Calculate(GeoCoordinate from, GeoCoordinate to)
{
try
{
lock(_graph)
{
var router = Router.CreateCHFrom(_graph, new CHRouter(), new OsmRoutingInterpreter());
// The exception happens here below
var fromResolved = router.Resolve(Vehicle.Car, from);
var toResolved = router.Resolve(Vehicle.Car, to);
if(fromResolved != null && toResolved !=null)
{
return router.Calculate(Vehicle.Car, fromResolved, toResolved);
}
}
}
catch(Exception ex)
{
OsmSharp.Logging.Log.TraceEvent("Router", OsmSharp.Logging.TraceEventType.Critical, "Unhandled exception occured: {0}", ex.ToString());
}
return null;
}
And the exception:
> {ProtoBuf.ProtoException: Invalid wire-type; this usually means you
> have over-written a file without truncating or setting the length; see
> http://stackoverflow.com/q/2152978/23354 at
> ProtoBuf.ProtoReader.ReadSingle () ...
I didnt overwrite the file (kempen-big.contracted.mobile.routing) just added it as a linked file in the project. Any ideas how I can solve this issue?

Well, the first thing to try is to check that the contents of the Stream you are reading (via GetManifestResourceStream) contains exactly the contents you are expecting, and not some wrapper or otherwise-corrupt mess. If you have some checksum algorithm you can run: great! Checking just the .Length would be a great start. Otherwise, you could cheat (just for the purposes of validating the contents) by getting the hex:
using (var ms = new MemoryStream())
{
stream.CopyTo(ms);
string hex = BitConverter.ToString(
ms.GetBuffer(), 0, (int)ms.Length);
// dump this string, and compare it to the same output run on the
// oringal file; they should be identical
}
Note that this duplicates the contents in-memory, purely so we can get a byte[] (oversized) to get the hex from - it isn't intended for "real" code, but until you are sure that the contents are correct, all other bets are off. I strongly suspect that you'll find that the contents are not identical to the contents in the original file. Note that I'm also implicitly assuming that the original file works fine in terms of deserialization. If the original file doesn't work: again, all bets are off.

Not finding local data files saved in my application

The process seemed quite simplistic at first, but there must be something that I am missing going forward with this task. There was a settings file that I wanted to create local to my application for storing a whole bunch of data (not preference worthy). I ended up saving the file with the following code snippet.
protected File createSettingsFileLocation(String fileNameF)
{
File directoryFile = context_.getDir("settings", Context.MODE_PRIVATE);
File settingsFile;
settingsFile = new File(directoryFile, fileNameF);
if (!settingsFile.exists())
{
try
{
settingsFile.createNewFile();
} catch(IOException e)
{
Log.e(MyConstants.LOG_TAG, "Could not create the file as intended within internal storage.");
return null;
}
}
return settingsFile;
}
and then proceeded to retrieve the file later by looking for it locally with the following code snippets.
public String getCurrentFileContainingSettings()
{
List<String >settingFilesInFolder = getLocalStorageFileNames();
if (settingFilesInFolder == null || settingFilesInFolder.isEmpty())
{
return null;
}
String pathToCurrentSettingsFile = settingFilesInFolder.get(0);
return pathToCurrentSettingsFile;
}
protected List<String> getLocalStorageFileNames()
{
return Arrays.asList(context_.fileList());
}
However, the settingFilesInFolder always returns no entries, so I get null back from the getCurrentFileContainingSettings(). As what I could see from the documentation it seems as thought I was doing it right. But, I must be missing something, so I was hoping that someone could point something out to me. I could potentially hard-code the file name once it has been created within the system in a preference file for access later the first time that the settings are created, but I shouldn't have to do something like that I would think.

fileList() only looks in getFilesDir(), not in its subdirectories, such as the one you created via getDir(). Use standard Java file I/O (e.g., list()) instead.

Is there a simpler way to do parsing in Java on Android?

I'm having difficulty performing what should be a simple task. Let's say I have a text file that states:
a = b
I want my program to read this file and output "b" whenever the user inputs "a". In Python or C++ I can accomplish this in around 7 lines or less.
However, I'm having difficulty finding a simple way to do this on Android. For example, one sample that I found here on SO had nearly 900 lines in 6 files.
Is there a simple way to parse a file and return a variable on Android that I am missing?

BufferedReader r = new BufferedReader(new FileReader(filename));
string s;
while(s = r.readLine()) {
//Oh hey, I got a line out of the file.
//In three lines of code.
//So what's all this Android-bashing about?
}

As long as you're happy with thea = b format used in properties files, you get 99% of the way to your goal with
Properties properties = new Properties();
try {
properties.load(new FileInputStream(filename));
} catch (IOException e) {
// the file is missing or is not in 'a = b' format
}
The, having got a variable key containing the string "a" from the user, the result of properties.getProperty ( key ) will equal "b" if the file contains the line a = b. I'm pretty sure you need more than that in C++ to load a map from a file and handle all the escaping and character encoding issues.
If the properties are held in a text file called mappings.properties in the assets folder of your Android project rather than in the user's file system, then you get at it like this:
final AssetManager am = getResources().getAssets();
final Properties properties = new Properties();
try {
properties.load( am.open("mappings.properties"));
} catch (IOException e) {
// the file is missing or is not in 'a = b' format
}
This next bit is borrowed from the android tutorial to show a toast message with 'b' in it if 'a' is entered in the edit box. Maybe here is where you get your line count from, as setting up a GUI with XML files and adding listeners in Java is fairly verbose compared with other languages. That's due to Java and XML syntax rather than the virtual machine.
final EditText edittext = (EditText) findViewById(R.id.edittext);
edittext.setOnKeyListener(new OnKeyListener() {
#Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
// If the event is a key-down event on the "enter" button
if ((event.getAction() == KeyEvent.ACTION_DOWN) &&
(keyCode == KeyEvent.KEYCODE_ENTER)) {
// Perform action on key press
Toast.makeText(YourOuterViewClass.this,
properties.getProperty(edittext.getText().toString()),
Toast.LENGTH_SHORT).show();
return true;
}
return false;
}
});

You definitely don't need hundreds of lines of code to achieve this. It can be done in a few lines. I don't know what examples you were looking at but they were probably doing way more than what you are describing.