CachedField

master: develop:

Wrapper for expensive resources. Allows you to separate concerns of how to load the values from how to use them.

Interface description

Each Cached field supports following methods:

void postValue();

which posts current value when it's ready - most often that happens immediately if the value was already calculated/fetched, or after time needed for it recalculation if session changed or it is first time that this value is requested.

void refresh();

that forces recalculation of the value (and then posts event),

FieldState getState();

that returns current state of the field (this is typically used to display some kind of progress indicator to user).

void drop();

that orders cached value to be forgotten, so the memory can be reclaimed.

void addStateListener(FieldStateListener listener);
boolean removeStateListener(FieldStateListener listener);

Allows adding and removing listeners that will be informed about FieldState changes(like starting to load value). This can be useful for displaying busy indicator in graphical applications.

Parametric fields

In case your value depends on some argument (for example API GET call that requires item ID) you can use CachedFieldWithArg. It supports same methods but requires you to pass argument to post and refresh calls. Only one value will be cached at the time, so changing argument will force a refresh.

If you ask CachedFieldWithArg for value with new argument before last call had chance to finish, SuccessListenerWithArg will be informed only about values with current argument. Previous call will be assumed obsolete, and its return value(if any) will be discarded and ErrorListenerWithArg (if any) will be called instead.

Parametric field classes have withArg suffix, and behave same as their no arg counterparts. Split exist only to enforce passing extra argument to methods that depend on it.

Controlling execution threads

By default loading of value is executed asynchronously on background thread, and listeners are called without thread switching. This means that by default you can safely invoke CachedField methods on UI thread without blocking it.

If you prefer to have more control over Threads on which value loading (or calling state listeners) you can specify custom ExecutorService and Executor (Either by passing constructor arguments to CachedFieldImpl directly or by setting defaults, or by builder )

CachedEndpoint

If you have API calls that do not fit into CachedField (most of non GET calls) you may prefer to use CachedEndpoint instead.

CachedEndpoint differences compared toCachedField(other than different names and packages):

• call() will always make an API call (even if value was already loaded with same arguments - like refresh())
• After failed call value is not dropped, and instead Exception is cached.
• EndpointState compared to FieldState have additional state CALL_FAILED
• Instead of separate ErrorListener and SuccessListener there is only one CallEndListener
• Cached value can be read directly by getStateAndValue()
• Adding EndpointStateListener results in it being informed about current state and value

Some of the CachedEndpoint specification is still not decided (mostly behaviour with multiple concurrent calls to one endpoint). Therefore it should be considered beta feature, as the behaviour may be adjusted in the future.

Session Id

Passing a provider of session id to CachedField allows it to check if cached value is still valid. For example it will ensure that when user switches accounts data from old account will never be shown (even if it arrives after account switch). Depending on application either session token, user name, or even empty string may be valid for this check. As sessionProvider is standard Provider you may use Dependency Injection like Dagger to create it (example) By default sessionProvider must be passed to CachedFieldImpl constructor, but some libraries like OttoCachedField allow to set default provider for whole project.

Getting started

Including in projects

Add as a dependency to your build.gradle:

• recommended for pure Java:

compile 'com.byoutline.cachedfield:cachedfield:1.5.3'

• recommended for Android (comes with most unversal builder that allows to build any other CachedField and supports Android Data Binding:

compile 'com.byoutline.ottocachedfield:observablecachedfield:1.1.0'

Init common settings

To avoid passing same values to each of your CachedFields put following into your code (typically to Application onCreate method).

OttoCachedField.init(sessionIdProvider, bus);

where bus is Otto bus instance, and sessionIdProvider is a Provider of current session. Provider is supposed to return same string as long as same user is logged in. Typically it something like authorization header for your API calls.

Declare your fields

Start by typing CachedFieldBuilder(). and follow autocompletion in your IDE through fluent interface. This will allow you to build CachedField that you need. For example you will be able to select:

• whether you require argument or not (.withValueProvider*)
• whether you want to post results by bus ( withSuccessEvent, withErrorEvent)
• whether you want to use DataBinding Observable (asObservable)
• whether you want to get CachedEndpoint instead of CachedField
• whether you want to use custom or default session provider or bus

for example

new CachedFieldBuilder()
        .withValueProvider(service::getValueFromApi)
        .asObservable()
        .build();

Note: if you are using Retrofit 2 and your service returns Call you can convert it to Provider with apiValueProv static method.

Testing with Espresso on Android

For instrumented tests on Android you may want to register your Cached Fields/Endpoints as IdlingResources. Easiest way to do that is creating with CachedFieldIdlingResource.from method that takes any amount of Cached Fields/Endpoints and notifies Espresso when any of them is working. For example your test set up may look like this:

private CachedFieldIdlingResource cachedFieldIdlingResource;

@Before
public void registerIdlingResources() {
    cachedFieldIdlingResource = CachedFieldIdlingResource.from(field1, field2, field3);
    Espresso.registerIdlingResources(cachedFieldIdlingResource);
}

@After
public void unregisterIdlingResources() {
    Espresso.unregisterIdlingResources(cachedFieldIdlingResource);
}

Displaying progress on Android

If you want to have indicator that is synchronized with state of your CachedField(s) check out WaitLayout which will display spinner any time any of the registered Fields/Endpoints is working.