VolumeProviderCompat.java

/*
 * Copyright (C) 2014 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 android.support.v4.media;

import android.os.Build;
import android.support.annotation.IntDef;
import android.support.v4.media.session.MediaSessionCompat;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

/**
 * Handles requests to adjust or set the volume on a session. This is also used
 * to push volume updates back to the session after a request has been handled.
 * You can set a volume provider on a session by calling
 * {@link MediaSessionCompat#setPlaybackToRemote}.
 */
public abstract class VolumeProviderCompat {

    /**
     * @hide
     */
    @IntDef({VOLUME_CONTROL_FIXED, VOLUME_CONTROL_RELATIVE, VOLUME_CONTROL_ABSOLUTE})
    @Retention(RetentionPolicy.SOURCE)
    public @interface ControlType {}

    /**
     * The volume is fixed and can not be modified. Requests to change volume
     * should be ignored.
     */
    public static final int VOLUME_CONTROL_FIXED = 0;

    /**
     * The volume control uses relative adjustment via
     * {@link #onAdjustVolume(int)}. Attempts to set the volume to a specific
     * value should be ignored.
     */
    public static final int VOLUME_CONTROL_RELATIVE = 1;

    /**
     * The volume control uses an absolute value. It may be adjusted using
     * {@link #onAdjustVolume(int)} or set directly using
     * {@link #onSetVolumeTo(int)}.
     */
    public static final int VOLUME_CONTROL_ABSOLUTE = 2;

    private final int mControlType;
    private final int mMaxVolume;
    private int mCurrentVolume;
    private Callback mCallback;

    private Object mVolumeProviderObj;

    /**
     * Create a new volume provider for handling volume events. You must specify
     * the type of volume control and the maximum volume that can be used.
     *
     * @param volumeControl The method for controlling volume that is used by
     *            this provider.
     * @param maxVolume The maximum allowed volume.
     * @param currentVolume The current volume.
     */
    public VolumeProviderCompat(@ControlType int volumeControl, int maxVolume, int currentVolume) {
        mControlType = volumeControl;
        mMaxVolume = maxVolume;
        mCurrentVolume = currentVolume;
    }

    /**
     * Get the current volume of the provider.
     *
     * @return The current volume.
     */
    public final int getCurrentVolume() {
        return mCurrentVolume;
    }

    /**
     * Get the volume control type that this volume provider uses.
     *
     * @return The volume control type for this volume provider
     */
    @ControlType
    public final int getVolumeControl() {
        return mControlType;
    }

    /**
     * Get the maximum volume this provider allows.
     *
     * @return The max allowed volume.
     */
    public final int getMaxVolume() {
        return mMaxVolume;
    }

    /**
     * Set the current volume and notify the system that the volume has been
     * changed.
     *
     * @param currentVolume The current volume of the output.
     */
    public final void setCurrentVolume(int currentVolume) {
        mCurrentVolume = currentVolume;
        Object volumeProviderObj = getVolumeProvider();
        if (volumeProviderObj != null) {
            VolumeProviderCompatApi21.setCurrentVolume(volumeProviderObj, currentVolume);
        }
        if (mCallback != null) {
            mCallback.onVolumeChanged(this);
        }
    }

    /**
     * Override to handle requests to set the volume of the current output.
     *
     * @param volume The volume to set the output to.
     */
    public void onSetVolumeTo(int volume) {
    }

    /**
     * Override to handle requests to adjust the volume of the current output.
     *
     * @param direction The direction to adjust the volume in.
     */
    public void onAdjustVolume(int direction) {
    }

    /**
     * Sets a callback to receive volume changes.
     * <p>
     * Used internally by the support library.
     * <p>
     */
    public void setCallback(Callback callback) {
        mCallback = callback;
    }

    /**
     * Gets the underlying framework {@link android.media.VolumeProvider} object.
     * <p>
     * This method is only supported on API 21+.
     * </p>
     *
     * @return An equivalent {@link android.media.VolumeProvider} object, or null if none.
     */
    public Object getVolumeProvider() {
        if (mVolumeProviderObj != null || Build.VERSION.SDK_INT < 21) {
            return mVolumeProviderObj;
        }

        mVolumeProviderObj = VolumeProviderCompatApi21.createVolumeProvider(
                mControlType, mMaxVolume, mCurrentVolume, new VolumeProviderCompatApi21.Delegate() {

            @Override
            public void onSetVolumeTo(int volume) {
                VolumeProviderCompat.this.onSetVolumeTo(volume);
            }

            @Override
            public void onAdjustVolume(int direction) {
                VolumeProviderCompat.this.onAdjustVolume(direction);
            }
        });
        return mVolumeProviderObj;
    }

    /**
     * Listens for changes to the volume.
     */
    public static abstract class Callback {
        public abstract void onVolumeChanged(VolumeProviderCompat volumeProvider);
    }
}