TransportMediator

public class TransportMediator
extends TransportController

助手实现媒体传输控制（播放，暂停，跳过和其他媒体操作）。 照顾重要事件和高级功能，如RemoteControlClient 。 该课程旨在作为交通控制（无论是屏幕控制，硬件按钮，遥控器）还是实际玩家之间的中介。 玩家由一个TransportPerformer代表，必须提供给该课程。 希望控制和显示播放器状态的屏幕控件应通过调用TransportController界面来完成。

这是一个简单但相当完整的围绕此课程构建的视频播放器示例。 请注意，此处使用的MediaController类不是标准Android框架中包含的类，而是自定义实现。 真正的应用程序通常会实现自己的传输控制，或者您可以将实现从Support4Demos中复制出来。

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

Inherited methods
From class android.support.v4.media.TransportController abstract int getBufferPercentage() 以百分比（0-100）检索媒体流已缓冲到本地设备的金额。 abstract long getCurrentPosition() 以毫秒为单位检索媒体流中的当前播放位置。 abstract long getDuration() 检索媒体流的总持续时间，以毫秒为单位。 abstract int getTransportControlFlags() 检索该传输支持的媒体传输控制按钮的标志。 abstract boolean isPlaying() 返回玩家是否正在播放其流。 abstract void pausePlaying() 请求播放器暂停播放并保持当前位置。 abstract void registerStateListener(TransportStateListener listener) 开始监听播放状态的变化。 abstract void seekTo(long pos) 移动到媒体流中的新位置。 abstract void startPlaying() 请求播放器在当前位置开始播放。 abstract void stopPlaying() 要求播放器停止播放; 它可以以任何适当的方式清除其状态。 abstract void unregisterStateListener(TransportStateListener listener) 停止收听播放状态的变化。
From class java.lang.Object Object clone() 创建并返回此对象的副本。 boolean equals(Object obj) 指示其他某个对象是否“等于”这一个。 void finalize() 当垃圾收集确定没有更多对该对象的引用时，由对象上的垃圾回收器调用。 final Class<?> getClass() 返回此 Object的运行时类。 int hashCode() 返回对象的哈希码值。 final void notify() 唤醒正在等待该对象监视器的单个线程。 final void notifyAll() 唤醒在该对象监视器上等待的所有线程。 String toString() 返回对象的字符串表示形式。 final void wait(long millis, int nanos) 导致当前线程等待，直到另一个线程为该对象调用 notify()方法或 notifyAll()方法，或者某个其他线程中断当前线程，或者经过了一定的实时时间。 final void wait(long millis) 导致当前线程等待，直到另一个线程调用此对象的 notify()方法或 notifyAll()方法或经过了指定的时间量。 final void wait() 导致当前线程等待，直到另一个线程调用此对象的方法 notify()或方法 notifyAll() 。

Constants

int FLAG_KEY_MEDIA_FAST_FORWARD

int FLAG_KEY_MEDIA_NEXT

int FLAG_KEY_MEDIA_PAUSE

int FLAG_KEY_MEDIA_PLAY

int FLAG_KEY_MEDIA_PLAY_PAUSE

int FLAG_KEY_MEDIA_PREVIOUS

int FLAG_KEY_MEDIA_REWIND

int FLAG_KEY_MEDIA_STOP

int KEYCODE_MEDIA_PAUSE

int KEYCODE_MEDIA_PLAY

int KEYCODE_MEDIA_RECORD

Public constructors

TransportMediator (Activity activity, 
                TransportPerformer callbacks)

TransportMediator (View view, 
                TransportPerformer callbacks)

Public methods

void destroy ()

boolean dispatchKeyEvent (KeyEvent event)

int getBufferPercentage ()

long getCurrentPosition ()

long getDuration ()

Object getRemoteControlClient ()

int getTransportControlFlags ()

boolean isPlaying ()

void pausePlaying ()

void refreshState ()

void registerStateListener (TransportStateListener listener)

void seekTo (long pos)

void startPlaying ()

void stopPlaying ()

void unregisterStateListener (TransportStateListener listener)