A lightweight implementation of Promises/A+ specification.
Add the following dependency to build.gradle:
dependencies {
...
compile 'com.octopepper.promiser:android-promiser:1.0.2'
}
This library is written using Java 8 syntax.
Let's embrace the future ! 😄
To use this into Java 7, 6 and 5 projects, don't forget to install retrolambda by @orfjackal.
You can create a Promiser object like this :
Promiser<T, U> p = new Promiser<T, U>(
(Resolver<T> resolve, Rejecter<U> reject) -> {
// Place your asynchronous process here, and make sure
// to trigger resolve.run() or reject.run() when needed.
});<T> is the type of the result returned in case of success and <U> is the type of the result returned in case of error.
You can handle result and error cases like this now :
p.success((T result) -> {
// Handle success here
}).error((U err) -> {
// Handle error here
});If you want to do multiple asynchronous tasks sequentially use .then()
p.then((T result) -> {
// T instanceOf String
// example X = parseToInt(T)
}).then((X result) -> {
// Now X instanceOf int
});For example let's mock an asynchronous process using Retrofit v2
public Promiser<String, Integer> fetchUsers() {
return new Promiser<>((resolve, reject) -> {
retrofit.getService(IUserService.class).fetchUsers().enqueue(new Callback<String>() {
@Override
public void onResponse(Response<String> response) {
if (response.isSuccess())
resolve.run(response.body()); //resolving result
else
reject.run(response.code()); //rejecting error code
}
@Override
public void onFailure(Throwable t) {
reject.run(CodeError.Undefined.getCode()); //reject error
}
});
});
}Now we can handle the success or the error of this promise using the .success() and .error() callbacks :
fetchUsers()
.success(str -> {
// Handle success here
}).error(code -> {
// Handle error here
});fetchUsers()
.then(str -> {
// Parse Json to Object
}).then(users -> {
// Do something
});or even better:
fetchUsers()
.success(this::resultSucceeded)
.error(this::resultError);
private void resultSucceeded(String s) {
// Handle success here
}
private void resultError(Integer code) {
// Handle error here
}- Make
.then()accept a Promiser as a return type. The Promiser returned will have to be resolved.
fetchUser()
.then(user -> fetchPhotosByUser())
.then(photos -> {
// Do something
});