public interface

Observable<T>

 androidx.camera.core.Observable<T>

Overview

An observable stream which contains data or errors.

Summary

Methods
public voidaddObserver(java.util.concurrent.Executor executor, Observable.Observer<java.lang.Object> observer)

Adds an observer which will receive the stream of data.

public <any>fetchData()

Fetch the latest piece of data asynchronously.

public voidremoveObserver(Observable.Observer<java.lang.Object> observer)

Removes a previously added observer.

Methods

public <any> fetchData()

Fetch the latest piece of data asynchronously.

The returned future may also complete with an exception if the observable currently contains an error. If the observable has not yet been initialized with a value, the future may contain an java.lang.IllegalStateException.

Returns:

A future which will contain the latest value or an error.

public void addObserver(java.util.concurrent.Executor executor, Observable.Observer<java.lang.Object> observer)

Adds an observer which will receive the stream of data.

This is an asynchronous operation. Once the observer has been added, it will immediately be called with the latest value contained in the observable if it contains a value, or will be called once a value has been set on the observable.

All added observers should be removed with Observable.removeObserver(Observable.Observer) when no longer needed.

If the same observer is added twice, it will only be called on the last executor it was registered with.

Parameters:

executor: The executor which will be used to notify the observer of new data.
observer: The observer which will receive new data.

public void removeObserver(Observable.Observer<java.lang.Object> observer)

Removes a previously added observer.

Once removed, the observer will no longer receive data.

If the observer was not previously added, this operation will be a no-op.

Parameters:

observer: The observer to remove.

Source

/*
 * Copyright 2019 The Android Open Source Project
 *
 * 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 androidx.camera.core;

import android.annotation.SuppressLint;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import com.google.common.util.concurrent.ListenableFuture;

import java.util.concurrent.Executor;

/**
 * An observable stream which contains data or errors.
 *
 * @param <T> The type of the data in the stream.
 */
public interface Observable<T> {

    /**
     * Fetch the latest piece of data asynchronously.
     *
     * <p>The returned future may also complete with an exception if the observable currently
     * contains an error. If
     * the observable has not yet been initialized with a value, the future may contain an
     * {@link IllegalStateException}.
     *
     * @return A future which will contain the latest value or an error.
     */
    @NonNull
    ListenableFuture<T> fetchData();

    /**
     * Adds an observer which will receive the stream of data.
     *
     * <p>This is an asynchronous operation. Once the observer has been added, it will
     * immediately be called with the latest value contained in the observable if it contains a
     * value, or will be called once a value has been set on the observable.
     *
     * <p>All added observers should be removed with {@link #removeObserver(Observer)} when no
     * longer needed.
     *
     * <p>If the same observer is added twice, it will only be called on the last executor it was
     * registered with.
     *
     * @param executor The executor which will be used to notify the observer of new data.
     * @param observer The observer which will receive new data.
     */
    @SuppressLint("LambdaLast")
    // Remove after https://issuetracker.google.com/135275901
    void addObserver(@NonNull Executor executor, @NonNull Observer<T> observer);

    /**
     * Removes a previously added observer.
     *
     * <p>Once removed, the observer will no longer receive data.
     *
     * <p>If the observer was not previously added, this operation will be a no-op.
     *
     * @param observer The observer to remove.
     */
    void removeObserver(@NonNull Observer<T> observer);

    /**
     * A callback that can receive new values and errors from an {@link Observable}.
     *
     * @param <T> The type of the data being reported.
     */
    interface Observer<T> {
        /**
         * Called when the stream emits a new piece of data.
         *
         * @param value The new data value
         */
        void onNewData(@Nullable T value);

        /**
         * Called when the stream emits an error.
         *
         * @param t The error.
         */
        void onError(@NonNull Throwable t);
    }
}