TransportMediator

Class Overview

Helper for implementing a media transport control (with play, pause, skip, and other media actions). Takes care of both key events and advanced features like RemoteControlClient. This class is intended to serve as an intermediary between transport controls (whether they be on-screen controls, hardware buttons, remote controls) and the actual player. The player is represented by a single TransportPerformer that must be supplied to this class. On-screen controls that want to control and show the state of the player should do this through calls to the TransportController interface.

Here is a simple but fairly complete sample of a video player that is built around this class. Note that the MediaController class used here is not the one included in the standard Android framework, but a custom implementation. Real applications often implement their own transport controls, or you can copy the implementation here out of Support4Demos.

import android.support.v4.media.TransportMediator;
import android.support.v4.media.TransportPerformer;
import com.example.android.supportv4.R;

import android.app.ActionBar;
import android.content.Context;
import android.media.MediaPlayer;
import android.os.Handler;
import android.util.AttributeSet;
import android.view.KeyEvent;
import android.view.View;

import android.app.Activity;
import android.net.Uri;
import android.os.Bundle;
import android.widget.VideoView;

public class TransportControllerActivity extends Activity {

    /**
     * TODO: Set the path variable to a streaming video URL or a local media
     * file path.
     */
    private Content mContent;
    private TransportMediator mTransportMediator;
    private MediaController mMediaController;

    /**
     * Handle actions from on-screen media controls.  Most of these are simple re-directs
     * to the VideoView; some we need to capture to update our state.
     */
    TransportPerformer mTransportPerformer = new TransportPerformer() {
        @Override public void onStart() {
            mContent.start();
        }

        @Override public void onStop() {
            mContent.pause();
        }

        @Override public void onPause() {
            mContent.pause();
        }

        @Override public long onGetDuration() {
            return mContent.getDuration();
        }

        @Override public long onGetCurrentPosition() {
            return mContent.getCurrentPosition();
        }

        @Override public void onSeekTo(long pos) {
            mContent.seekTo((int)pos);
        }

        @Override public boolean onIsPlaying() {
            return mContent.isPlaying();
        }

        @Override public int onGetBufferPercentage() {
            return mContent.getBufferPercentage();
        }

        @Override public int onGetTransportControlFlags() {
            int flags = TransportMediator.FLAG_KEY_MEDIA_PLAY
                    | TransportMediator.FLAG_KEY_MEDIA_PLAY_PAUSE
                    | TransportMediator.FLAG_KEY_MEDIA_STOP;
            if (mContent.canPause()) {
                flags |= TransportMediator.FLAG_KEY_MEDIA_PAUSE;
            }
            if (mContent.canSeekBackward()) {
                flags |= TransportMediator.FLAG_KEY_MEDIA_REWIND;
            }
            if (mContent.canSeekForward()) {
                flags |= TransportMediator.FLAG_KEY_MEDIA_FAST_FORWARD;
            }
            return flags;
        }
    };

    /**
     * This is the actual video player.  It is the top-level content of
     * the activity's view hierarchy, going under the status bar and nav
     * bar areas.
     */
    public static class Content extends VideoView implements
            View.OnSystemUiVisibilityChangeListener, View.OnClickListener,
            ActionBar.OnMenuVisibilityListener, MediaPlayer.OnPreparedListener,
            MediaPlayer.OnCompletionListener, MediaPlayer.OnErrorListener {
        Activity mActivity;
        TransportMediator mTransportMediator;
        MediaController mMediaController;
        boolean mAddedMenuListener;
        boolean mMenusOpen;
        boolean mPaused;
        boolean mNavVisible;
        int mLastSystemUiVis;

        Runnable mNavHider = new Runnable() {
            @Override public void run() {
                setNavVisibility(false);
            }
        };

        Runnable mProgressUpdater = new Runnable() {
            @Override public void run() {
                mMediaController.updateProgress();
                getHandler().postDelayed(this, 1000);
            }
        };

        public Content(Context context, AttributeSet attrs) {
            super(context, attrs);
            setOnSystemUiVisibilityChangeListener(this);
            setOnClickListener(this);
            setOnPreparedListener(this);
            setOnCompletionListener(this);
            setOnErrorListener(this);
        }

        public void init(Activity activity, TransportMediator transportMediator,
                MediaController mediaController) {
            // This called by the containing activity to supply the surrounding
            // state of the video player that it will interact with.
            mActivity = activity;
            mTransportMediator = transportMediator;
            mMediaController = mediaController;
            pause();
        }

        @Override protected void onAttachedToWindow() {
            super.onAttachedToWindow();
            if (mActivity != null) {
                mAddedMenuListener = true;
                mActivity.getActionBar().addOnMenuVisibilityListener(this);
            }
        }

        @Override protected void onDetachedFromWindow() {
            super.onDetachedFromWindow();
            if (mAddedMenuListener) {
                mActivity.getActionBar().removeOnMenuVisibilityListener(this);
            }
            mNavVisible = false;
        }

        @Override public void onSystemUiVisibilityChange(int visibility) {
            // Detect when we go out of nav-hidden mode, to clear our state
            // back to having the full UI chrome up.  Only do this when
            // the state is changing and nav is no longer hidden.
            int diff = mLastSystemUiVis ^ visibility;
            mLastSystemUiVis = visibility;
            if ((diff&SYSTEM_UI_FLAG_HIDE_NAVIGATION) != 0
                    && (visibility&SYSTEM_UI_FLAG_HIDE_NAVIGATION) == 0) {
                setNavVisibility(true);
            }
        }

        @Override protected void onWindowVisibilityChanged(int visibility) {
            super.onWindowVisibilityChanged(visibility);

            // When we become visible or invisible, play is paused.
            pause();
        }

        @Override public void onClick(View v) {
            // Clicking anywhere makes the navigation visible.
            setNavVisibility(true);
        }

        @Override public void onMenuVisibilityChanged(boolean isVisible) {
            mMenusOpen = isVisible;
            setNavVisibility(true);
        }

        @Override
        public void onPrepared(MediaPlayer mp) {
            mMediaController.setEnabled(true);
        }

        @Override
        public void onCompletion(MediaPlayer mp) {
            mTransportMediator.pausePlaying();
            pause();
        }

        @Override
        public boolean onError(MediaPlayer mp, int what, int extra) {
            mTransportMediator.pausePlaying();
            pause();
            return false;
        }

        @Override public void start() {
            super.start();
            mPaused = false;
            setKeepScreenOn(true);
            setNavVisibility(true);
            mMediaController.refresh();
            scheduleProgressUpdater();
        }

        @Override public void pause() {
            super.pause();
            mPaused = true;
            setKeepScreenOn(false);
            setNavVisibility(true);
            mMediaController.refresh();
            scheduleProgressUpdater();
        }

        void scheduleProgressUpdater() {
            Handler h = getHandler();
            if (h != null) {
                if (mNavVisible && !mPaused) {
                    h.removeCallbacks(mProgressUpdater);
                    h.post(mProgressUpdater);
                } else {
                    h.removeCallbacks(mProgressUpdater);
                }
            }
        }

        void setNavVisibility(boolean visible) {
            int newVis = SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                    | SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                    | SYSTEM_UI_FLAG_LAYOUT_STABLE;
            if (!visible) {
                newVis |= SYSTEM_UI_FLAG_LOW_PROFILE | SYSTEM_UI_FLAG_FULLSCREEN
                        | SYSTEM_UI_FLAG_HIDE_NAVIGATION;
            }

            // If we are now visible, schedule a timer for us to go invisible.
            if (visible) {
                Handler h = getHandler();
                if (h != null) {
                    h.removeCallbacks(mNavHider);
                    if (!mMenusOpen && !mPaused) {
                        // If the menus are open or play is paused, we will not auto-hide.
                        h.postDelayed(mNavHider, 3000);
                    }
                }
            }

            // Set the new desired visibility.
            setSystemUiVisibility(newVis);
            mNavVisible = visible;
            mMediaController.setVisibility(visible ? VISIBLE : INVISIBLE);
            scheduleProgressUpdater();
        }
    }

    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        setContentView(R.layout.videoview);

        // Find the video player in our UI.
        mContent = (Content) findViewById(R.id.content);

        // Create transport controller to control video, giving the callback
        // interface to receive actions from.
        mTransportMediator = new TransportMediator(this, mTransportPerformer);

        // Create and initialize the media control UI.
        mMediaController = (MediaController) findViewById(R.id.media_controller);
        mMediaController.setMediaPlayer(mTransportMediator);

        // We're just playing a built-in demo video.
        mContent.init(this, mTransportMediator, mMediaController);
        mContent.setVideoURI(Uri.parse("android.resource://" + getPackageName() +
                "/" + R.raw.videoviewdemo));
    }

    @Override
    public boolean dispatchKeyEvent(KeyEvent event) {
        // We first dispatch keys to the transport controller -- we want it
        // to get to consume any media keys rather than letting whoever has focus
        // in the view hierarchy to potentially eat it.
        if (mTransportMediator.dispatchKeyEvent(event)) {
            return true;
        }

        return super.dispatchKeyEvent(event);
    }
}

Summary

[Expand] Inherited Methods
From class android.support.v4.media.TransportController abstract int getBufferPercentage() Retrieve amount, in percentage (0-100), that the media stream has been buffered on to the local device. abstract long getCurrentPosition() Retrieve the current playback location in the media stream, in milliseconds. abstract long getDuration() Retrieve the total duration of the media stream, in milliseconds. abstract int getTransportControlFlags() Retrieve the flags for the media transport control buttons that this transport supports. abstract boolean isPlaying() Return whether the player is currently playing its stream. abstract void pausePlaying() Request that the player pause its playback and stay at its current position. abstract void registerStateListener(TransportStateListener listener) Start listening to changes in playback state. abstract void seekTo(long pos) Move to a new location in the media stream. abstract void startPlaying() Request that the player start its playback at its current position. abstract void stopPlaying() Request that the player stop its playback; it may clear its state in whatever way is appropriate. abstract void unregisterStateListener(TransportStateListener listener) Stop listening to changes in playback state.
From class java.lang.Object Object clone() Creates and returns a copy of this Object. boolean equals(Object o) Compares this instance with the specified object and indicates if they are equal. void finalize() Invoked when the garbage collector has detected that this instance is no longer reachable. final Class<?> getClass() Returns the unique instance of Class that represents this object's class. int hashCode() Returns an integer hash code for this object. final void notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. final void notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. String toString() Returns a string containing a concise, human-readable description of this object. final void wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object. final void wait(long millis, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires. final void wait(long millis) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.