com.spotify.mobius.extras.Connectables Maven / Gradle / Ivy
/*
* -\-\-
* Mobius
* --
* Copyright (c) 2017-2018 Spotify AB
* --
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
* -/-/-
*/
package com.spotify.mobius.extras;
import com.spotify.mobius.Connectable;
import com.spotify.mobius.Connection;
import com.spotify.mobius.ConnectionLimitExceededException;
import com.spotify.mobius.functions.Consumer;
import com.spotify.mobius.functions.Function;
import javax.annotation.Nonnull;
/** Contains utility functions for working with {@link Connectables}. */
public final class Connectables {
private Connectables() {
// prevent instantiation
}
/**
* Convert a {@code Connectable} to a {@code Connectable} by applying the supplied
* function from J to I for each J received, before passing it on to a {@code Connection}
* received from the underlying {@code Connectable}. This makes {@link Connectable} a contravariant
* functor in functional programming terms.
*
* The returned {@link Connectable} doesn't enforce a connection limit, but of course the
* connection limit of the wrapped {@link Connectable} applies.
*
*
This is useful for instance if you want your UI to use a subset or a transformed version of
* the full model used in the {@code MobiusLoop}. As a simplified example, suppose that your model
* consists of a {@code Long} timestamp that you want to format to a {@code String} before
* rendering it in the UI. Your UI could then implement {@code Connectable}, and
* you could create a {@code Function} that does the formatting. The {@link
* com.spotify.mobius.MobiusLoop} would be outputting {@code Long} models that you need to convert
* to Strings before they can be accepted by the UI.
*
*
* public class Formatter {
* public static String format(Long timestamp) { ... }
* }
*
* public class MyUi implements Connectable {
* // other things in the UI implementation
*
* {@literal @}Override
* public Connection connect(Consumer output) {
* return new Connection() {
* {@literal @}Override
* public void accept(String value) {
* // bind the value to the right UI element
* }
*
* {@literal @}Override
* public void dispose() {
* // dispose of any resources, if needed
* }
* }
* }
* }
*
* // Then, to connect the UI to a MobiusLoop.Controller with a Long model:
* MobiusLoop.Controller controller = ... ;
* MyUi myUi = ... ;
*
* controller.connect(Connectables.contramap(Formatter::format, myUi));
*
*
* @param mapper the mapping function to apply
* @param connectable the underlying connectable
* @param the type the underlying connectable accepts
* @param the type the resulting connectable accepts
* @param the output type; usually the event type
*/
@Nonnull
public static Connectable contramap(
final Function mapper, final Connectable connectable) {
return new Connectable() {
@Nonnull
@Override
public Connection connect(Consumer output) throws ConnectionLimitExceededException {
final Connection delegateConnection = connectable.connect(output);
return new Connection() {
@Override
public void accept(J value) {
delegateConnection.accept(mapper.apply(value));
}
@Override
public void dispose() {
delegateConnection.dispose();
}
};
}
};
}
}