一些必備的背景知識,理解以下知識將有助於編寫AIDL通信流程。
1. AIDL是什麼?
AIDL:Android Interface Definition Language,即Android接口定義語言。即Android平臺上使用的IDL交互式數據語言,定義了Android平臺IPC的模板。
2. AIDL的語法?
2.1) AIDL文件以 .aidl 爲後綴名;
2.2) 支持八種基本數據類型:byte、char、short、int、long、float、double、boolean,以及String,CharSequence;
2.3) List類型:List中的所有元素必須是AIDL支持的類型之一,或者是一個其他AIDL生成的接口,或者是定義的parcelable。List可以使用泛型。
2.4) Map類型:Map中的所有元素必須是AIDL支持的類型之一,或者是一個其他AIDL生成的接口,或者是定義的parcelable。Map是不支持泛型的。
2.5) AIDL定向tag:in,out,inout。添加在AIDL接口中表示數據通信的流向。
in: client -> server, 數據從客戶端流向服務端
out: server -> client,數據從服務端流向客戶端
inout:client <-> server,數據在服務端和客戶端雙向流通。
3. Android平臺IPC的幾種方式
3.1) Socket(套接字)
作爲更通用的接口,傳輸效率低,主要用於不同機器或跨網絡的通信;
3.2) Pipe(管道)
在創建時分配一個page大小的內存,緩存區大小比較有限;
3.3 MessageQueue(消息隊列)
消息隊列:信息複製兩次,額外的CPU消耗;不合適頻繁或信息量大的通信;
3.4 Anonymous shared memory(匿名共享內存)
無須複製,共享緩衝區直接付附加到進程虛擬地址空間,速度快;但進程間的同步問題操作系統無法實現,必須各進程利用同步工具解決;
3.5 Signal(信號量)
不適用於信息交換,更適用於進程中斷控制,比如非法內存訪問,殺死某個進程等。比如系統log中常見的SIGABRT 6 C 由abort(3)發出的退出指令,SIGKILL 9 AEF Kill信號,SIGSEGV 11 C 無效的內存引用等等。
3.6 Semaphore(信號量)
常作爲一種鎖機制,防止某進程正在訪問共享資源時,其他進程也訪問該資源。因此,主要作爲進程間以及同一進程內不同線程之間的同步手段。
3.7 Binder通信
(1) 從性能的角度
數據拷貝次數:Binder數據拷貝只需要一次,而管道、消息隊列、Socket都需要2次,但共享內存方式一次內存拷貝都不需要;從性能角度看,Binder性能僅次於共享內存。
(2) 從穩定性的角度
Binder是基於C/S架構的,簡單解釋下C/S架構,是指客戶端(Client)和服務端(Server)組成的架構,Client端有什麼需求,直接發送給Server端去完成,架構清晰明朗,Server端與Client端相對獨立,穩定性較好;而共享內存實現方式複雜,沒有客戶與服務端之別,需要充分考慮到訪問臨界資源的併發同步問題,否則可能會出現死鎖等問題;從這穩定性角度看,Binder架構優越於共享內存。
(3) 從安全的角度傳統Linux
IPC的接收方無法獲得對方進程可靠的UID/PID,從而無法鑑別對方身份;而Android作爲一個開放的開源體系,擁有非常多的開發平臺,App來源甚廣,因此手機的安全顯得額外重要;對於普通用戶,絕不希望從App商店下載偷窺隱射數據、後臺造成手機耗電等等問題,傳統Linux IPC無任何保護措施,完全由上層協議來確保。
(4) 語言層面的角度
Android是基於Java語言(面向對象的語句),而對於Binder恰恰也符合面向對象的思想,將進程間通信轉化爲通過對某個Binder對象的引用調用該對象的方法,而其獨特之處在於Binder對象是一個可以跨進程引用的對象,它的實體位於一個進程中,而它的引用卻遍佈於系統的各個進程之中。相比而言,Binder通信在安全性、性能方面都有比較明顯的優勢。
Binder通信往往通過ioctl等方法跟內核空間的驅動進行交互:
圖1
Binder的架構圖:
圖2
C/S架構設計:
圖3
Android系統中Broadcast、ContentProvider、Message都能跨進程通訊,其根本原理都是Binder通信。可見Binder通信並非必須通過AIDL。
4. 序列化和反序列化
Android的進程都有獨立的內存空間,相互間不能訪問。想要在進程間數據通信,就需要將數據做序列化和反序列化。Android中對數據序列化有兩種方法:一種是實現Serializable接口另一種是實現Parcelable接口。Parcelable是android特有的序列化API,它的出現是爲了解決Serializable在序列化的過程中消耗資源嚴重的問題,但是因爲本身使用需要手動處理序列化和反序列化過程,會與具體的代碼綁定,使用較爲繁瑣,一般只獲取內存數據的時候使用。
簡單介紹下Parcelable的兩個過程:序列化、反序列化。
序列化:
@Override
publicvoid writeToParcel(Parcel dest, int flags) {
}
反序列化:
classBean {
}
publicstatic final Creator< Bean > CREATOR = new Creator< Bean >() {
@Override
public User createFromParcel(Parcelsource) {
return null;
}
@Override
public User[] newArray(int size) {
return new Bean [size];
}
};
5、AIDL的使用示例
在App 1中分享一個媒體文件(例如MP3)給另一個App 2。App 1中可以播放這個媒體文件,展示上傳文件進度。App 2可以播放傳輸過來的媒體文件。列舉下Server端和Client端需要做的事情:
a) AIDL通信過程中,Server端需要做什麼?
創建aidl文件以及數據通信類型,確認數據流向,後臺Service,在Service中埋入樁(Stub),以及在AndroidManifest.xml中聲明該Service。
b) AIDL通信過程中,Client端需要做什麼?
創建aidl文件以及數據通信類型(和Server端要保持一致),在activity或者適當位置bindService,bindService中的參數ServiceConnection,調用aidl接口函數傳遞數據。
值得注意的是,Client端不是必須要有Activity來傳遞數據,很多例子中都以Activity來演示,一個是方便看到數據通信結果,另一個是Activity有完整的生命週期,binder通信可以選擇在onCreate中bindService,在onStop中unbindService,這樣能有效回收資源。
5.1 明確Client端和Server端
從需求關係看:
1) App 1作爲數據提供方,需要源源不斷的將數據傳給App 2;
2) App 2作爲頁面(Activity)結果展示,更適合作客戶端。
定義App 1爲Server端, App 2作爲Client端。分別創建App 1和App 2,以及對應的MainActivity,相關的aidl文件,App 1創建Service,以及對應的樁(Stub)。
(ps:不過,如果反過來App 1作爲客戶端,主動調用AIDL接口獲取App 2傳過來的數據,思路也是通的。不過數據流向需要調整。)
5.2 確定接口以及數據流向
媒體文件的傳遞,確定接口:
// 通知文件傳輸流程開始
void onMediaShareStart(in String name);
//文件分段傳輸數據
void onMediaSharing(in MediaData data);
//通知文件傳輸結束
void onMediaShareFinish();
數據從當前頁面上傳到server端,數據流向爲Client端到Server端,接口參數配置in。
5.3創建AIDL文件
先從Server端開始。創建aidl文件:IMediaShareInterface.aidl、MediaData.aidl和MediaData.java。
//IMediaShareInterface.aidl
package com.cloudyhill.mediashare;
// Declare any non-default types here withimport statements
import com.cloudyhill.mediashare.MediaData;
interface IMediaShareInterface {
void onMediaShareStart(in String name);
void onMediaSharing(in MediaData data);
void onMediaShareFinish();
}
MediaData.aidl:
packagecom.cloudyhill.mediashare;
// Declare anynon-default types here with import statements
parcelable MediaData;
實現序列化的MediaData類,即文件MediaData.java,注意類的包名和類名和MediaData.aidl保持一致,否則會報錯。
MediaData.java:
package com.cloudyhill.mediashare;
import android.os.Parcel;
import android.os.Parcelable;
public class MediaData implements Parcelable {
private StringmFileName;
private int mMediaDataSize;
private byte[]mMediaDataArray;
public MediaData() {
}
protected MediaData(String name,int size,byte[] data) {
mFileName = name;
mMediaDataSize = size;
mMediaDataArray = data;
}
protected MediaData(Parcel in) {
readFromParcel(in);
}
public String getFileName() {
return mFileName;
}
public void setFileName(String name) {
mFileName = name;
}
public int getMediaDataSize() {
return mMediaDataSize;
}
public byte[] getMediaDataArray() {
return mMediaDataArray;
}
public void setMediaDataArray(byte[] array) {
mMediaDataArray = array;
mMediaDataSize = array.length;
}
public static final CreatorCREATOR = new Creator() {
@Override
public MediaData createFromParcel(Parcel in) {
return new MediaData(in);
}
@Override
public MediaData[] newArray(int size) {
return new MediaData[size];
}
};
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel parcel,int flags) {
parcel.writeString(mFileName);
parcel.writeInt(mMediaDataSize);
parcel.writeByteArray(mMediaDataArray);
}
public void readFromParcel(Parcel reply) {
mFileName = reply.readString();
mMediaDataSize = reply.readInt();
mMediaDataArray = reply.createByteArray();
}
}
5.4 Server端
創建Server端後臺運行的MediaShareService,Client端將通過bindService與之建立聯繫。
package com.cloudyhill.mediashareserver;
import android.app.Service;
import android.content.Intent;
import android.os.Environment;
import android.os.IBinder;
import android.os.RemoteException;
import android.util.Log;
import androidx.annotation.Nullable;
import com.cloudyhill.mediashare.IMediaShareInterface;
import com.cloudyhill.mediashare.MediaData;
import com.cloudyhill.mediashareserver.common.Config;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
public class MediaShareServiceextends Service {
private static final StringTAG = Config.LOG_TAG +"Srv";
private static MediaShareServicesInstance =null;
private long mMediaFileTotalSize;
private StringmMediaFileName;
private IMediaShareInterface.Stub mIMediaShareMgr = new IMediaShareInterface.Stub() {
@Override
public void onMediaShareStart(String name) throws RemoteException {
Log.d(TAG,"<onMediaShareStart>");
mMediaFileName = name;
mMediaFileTotalSize =0;
Log.d(TAG,"<onMediaShareStart>, mMediaFileName = " +mMediaFileName);
createMediaFile(mMediaFileName);
}
@Override
public void onMediaSharing(MediaData data) throws RemoteException {
Log.d(TAG,"<onMediaSharing>");
int size = data.getMediaDataSize();
Log.d(TAG,"<onMediaSharing>, size = " + size);
mMediaFileTotalSize += size;
writeMediaFile(data.getMediaDataArray(), size);
}
@Override
public void onMediaShareFinish() throws RemoteException {
Log.d(TAG,"<onMediaShareFinish>, mMediaFileTotalSize = " +mMediaFileTotalSize);
Intent intent =new Intent();
intent.setAction(Config.ACTION_MEDIA_SHARE_FINISH);
intent.putExtra(Config.EXTRA_MEDIA_SHARE_RESULT,mMediaFileTotalSize);
sendBroadcast(intent);
}
};
public MediaShareService() {
Log.d(TAG,"<MediaShareService>");
}
public MediaShareService getInstance() {
if (sInstance ==null) {
synchronized (this) {
if (sInstance == null) {
sInstance = new MediaShareService();
}
}
}
return sInstance;
}
@Nullable
@Override
public IBinder onBind(Intent intent) {
Log.d(TAG,"<onBind>");
return mIMediaShareMgr;
}
@Override
public void onCreate() {
super.onCreate();
Log.d(TAG,"<onCreate>");
}
@Override
public int onStartCommand(Intent intent,int flags,int startId) {
Log.d(TAG,"<onStartCommand>");
if (intent == null) {
return START_STICKY;
}
return START_STICKY;
}
@Override
public void onDestroy() {
Log.d(TAG,"<onDestroy>");
super.onDestroy();
}
private void createMediaFile(String name) {
Log.d(TAG,"<createMediaFile>, name = " + name);
File sdcard = Environment.getExternalStorageDirectory();
File file = new File(sdcard, name);
Log.d(TAG,"<createMediaFile>, file = " + file);
mMediaFileName = file.getAbsolutePath();
if (file.exists()) {
Log.d(TAG,"<createMediaFile>, file exist, delete");
file.delete();
}
try {
Log.d(TAG,"<createMediaFile>, create new file.");
file.createNewFile();
} catch (IOException e) {
Log.e(TAG,"<createMediaFile>, e = " + e);
}
}
private void writeMediaFile(byte[] array,int size) {
Log.d(TAG,"<writeMediaFile>");
File file =new File(mMediaFileName);
if (!file.exists()) {
try {
Log.d(TAG,"<writeMediaFile>, create new file.");
file.createNewFile();
} catch (IOException e) {
Log.e(TAG,"<writeMediaFile>, e = " + e);
}
}
try {
// append write the file
FileOutputStream fos =new FileOutputStream(file,true);
fos.write(array);
fos.flush();
fos.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
5.5 Client端
將之前的aidl文件和序列化的MediaData.java複製過去,注意包名以及位置。編寫用於上傳數據的MediaShareClientActivity
package com.cloudyhill.mediashareclient;
import android.app.Activity;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.IBinder;
import android.os.Looper;
import android.os.Message;
import android.os.RemoteException;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import com.cloudyhill.mediashare.IMediaShareInterface;
import com.cloudyhill.mediashare.MediaData;
import com.cloudyhill.mediashareclient.common.Config;
import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import static com.cloudyhill.mediashareclient.common.Config.MSG_MEDIA_FILE_SHARE;
import static com.cloudyhill.mediashareclient.common.Config.MSG_UPDATE_PROGRESS;
public class MediaShareClientActivity extends Activity implements View.OnClickListener {
private static final StringTAG = Config.LOG_TAG +"Activity";
private ContextmContext;
private MediaPlayermMediaPlayer;
private StringmMediaFileName = Config.FILE_NAME;
private long mMediaFileTotalSize;
private boolean mIsPlaying;
private TextViewmMediaFileText;
private TextViewmMediaProgressText;
private ButtonmPlayBtn;
private ButtonmShareBtn;
private IMediaShareInterfacemIMediaShare;
private HandlerThreadmHandlerThread;
private MessageHandlermMsgHandler;
private MainHandlermMainHandler;
private ServiceConnection mServiceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName componentName, IBinder service) {
Log.d(TAG,"<onServiceConnected>");
if (service !=null) {
try {
service.linkToDeath(mDeathRecipient,0);
}catch (RemoteException e) {
e.printStackTrace();
}
}
// step 2, notify media share start
mMediaFileTotalSize = 0;
// 關鍵點,獲取Server端接口類型
mIMediaShare = IMediaShareInterface.Stub.asInterface(service);
if (mIMediaShare !=null) {
try {
// 調用Server端接口
mIMediaShare.onMediaShareStart(Config.FILE_NAME);
} catch (RemoteException e) {
e.printStackTrace();
}
}
// step 3, send message
mMsgHandler.sendEmptyMessage(MSG_MEDIA_FILE_SHARE);
}
@Override
public void onServiceDisconnected(ComponentName componentName) {
Log.d(TAG,"<onServiceDisconnected>");
}
};
IBinder.DeathRecipient mDeathRecipient = new IBinder.DeathRecipient() {
@Override
public void binderDied() {
Log.d(TAG,"<binderDied>");
attemptBindService();
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mContext = getApplicationContext();
initViews();
initData();
}
@Override
protected void onStart() {
super.onStart();
Log.d(TAG,"<onStart>");
}
@Override
protected void onStop() {
super.onStop();
Log.d(TAG,"<onStart>");
attemptUnbindService();
}
@Override
public void onClick(View view) {
Log.d(TAG,"<onClick>");
int resId = view.getId();
switch (resId) {
case R.id.play:
if (mIsPlaying) {
pausePlayMusic();
} else {
startPlayMusic();
}
break;
case R.id.share:
handleShare();
break;
default:
break;
}
}
private void initViews() {
Log.d(TAG,"<initViews>");
mMediaFileText = (TextView) findViewById(R.id.share_name);
mMediaFileText.setText(mMediaFileName);
Log.d(TAG,"<initViews>, media file name = " +mMediaFileName);
mMediaProgressText = (TextView) findViewById(R.id.progress_text);
mPlayBtn = (Button) findViewById(R.id.play);
mPlayBtn.setOnClickListener(this);
mShareBtn = (Button) findViewById(R.id.share);
mShareBtn.setOnClickListener(this);
}
private void initData() {
Log.d(TAG,"<initData>");
mHandlerThread =new HandlerThread("MediaShareThread");
mHandlerThread.start();
mMsgHandler = new MessageHandler(mHandlerThread.getLooper());
mMainHandler = new MainHandler(Looper.getMainLooper());
}
private void updateMediaShareProgress() {
Log.d(TAG,"<updateMediaShareProgress>");
if (mMediaProgressText != null) {
mMediaProgressText.setText(String.valueOf(getMediaShareProgress()));
}
}
private void startPlayMusic() {
Log.d(TAG,"<pausePlayMusic>");
mMediaPlayer = MediaPlayer.create(mContext, R.raw.music_demo);
mMediaPlayer.start();
mPlayBtn.setText(R.string.pause);
mIsPlaying =true;
}
private void pausePlayMusic() {
Log.d(TAG,"<pausePlayMusic>");
if (mMediaPlayer != null) {
mMediaPlayer.pause();
}
mPlayBtn.setText(R.string.play);
mIsPlaying =false;
}
private synchronized long getMediaShareProgress() {
return mMediaFileTotalSize;
}
private synchronized void setMediaShareProgress(int size) {
mMediaFileTotalSize += size;
}
private void handleShare() {
Log.d(TAG,"<handleShare>");
// step 1
attemptBindService();
}
private void shareMediaFile() {
Log.d(TAG,"<shareMediaFile>");
boolean result =false;
InputStream is = getResources().openRawResource(R.raw.music_demo);
try {
result = readMediaFile(is);
}catch (IOException err) {
Log.e(TAG,"<shareMediaFile>, err = " + err);
}
Log.d(TAG,"<shareMediaFile>, result = " + result);
}
private boolean readMediaFile(InputStream is)throws IOException {
boolean result = false;
BufferedInputStream bis = new BufferedInputStream(is);
MediaData mediaData =new MediaData();
byte[] data =new byte[256*1024];
int size;
while ((size = bis.read(data)) != -1) {
Log.d(TAG,"<readMediaFile>, size = " + size);
setMediaShareProgress(size);
mMainHandler.sendEmptyMessage(MSG_UPDATE_PROGRESS);
mediaData.setMediaDataArray(data);
try {
if (mIMediaShare !=null) {
mIMediaShare.onMediaSharing(mediaData);
}
}catch (RemoteException e) {
e.printStackTrace();
}
}
Log.d(TAG,"<readMediaFile>, break while, size = " + size);
// step 4, notify media share finished.
try {
mIMediaShare.onMediaShareFinish();
}catch (RemoteException e) {
e.printStackTrace();
}
return result;
}
private void attemptBindService() {
Log.d(TAG,"<attemptBindService>");
Intent intent =new Intent();
intent.setAction("com.cloudyhill.action.MEDIA_SHARE");
intent.setPackage("com.cloudyhill.mediashareserver");
bindService(intent,mServiceConnection, Context.BIND_AUTO_CREATE);
}
private void attemptUnbindService() {
Log.d(TAG,"<attemptUnbindService>");
unbindService(mServiceConnection);
}
private class MessageHandler extends Handler {
private MessageHandler(Looper looper) {
super(looper);
}
@Override
public void handleMessage(Message msg) {
Log.d(TAG,"<handleMessage>, msg.what = " + msg.what);
switch (msg.what) {
case MSG_MEDIA_FILE_SHARE:
shareMediaFile();
break;
default:
break;
}
}
}
private class MainHandlerextends Handler {
private MainHandler(Looper looper) {
super(looper);
}
public void handleMessage(Message msg) {
Log.d(TAG,"<handleMessage>, MainHandler, msg.what = " + msg.what);
switch (msg.what) {
case MSG_UPDATE_PROGRESS:
updateMediaShareProgress();
break;
default:
break;
}
}
}
}
5.6 簡單看下byte[]的通信流程
從Client端的onMediaSharing入手,mIMediaShare是aidl編譯生成的IMediaShareInterface.java類。
BufferedInputStream bis =new BufferedInputStream(is);
MediaData mediaData =new MediaData();
byte[] data =new byte[256*1024];
int size;
while ((size = bis.read(data)) != -1) {
Log.d(TAG,"<readMediaFile>, size = " + size);
setMediaShareProgress(size);
mMainHandler.sendEmptyMessage(MSG_UPDATE_PROGRESS);
mediaData.setMediaDataArray(data);
try {
if (mIMediaShare !=null) {
// 調用aidl定義接口
mIMediaShare.onMediaSharing(mediaData);
}
} catch (RemoteException e) {
e.printStackTrace();
}
}
@Override
public void onMediaSharing(com.cloudyhill.mediashare.MediaData data) throws android.os.RemoteException {
// 獲取一個Parcel對象
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
try {
_data.writeInterfaceToken(DESCRIPTOR);
if ((data!=null)) {
_data.writeInt(1);
// 調用自定義Parcelable類的writeToParcel,data即MediaData
data.writeToParcel(_data,0);
} else {
_data.writeInt(0);
}
mRemote.transact(Stub.TRANSACTION_onMediaSharing, _data, _reply,0);
_reply.readException();
} finally {
_reply.recycle();
_data.recycle();
}
}
先是調用MediaData的writeToParcel,再調用mRemote(即Server端的IMediaShareInterface)發消息執行TRANSACTION_onMediaSharing。
查看MediaData的writeToParcel接口:
@Override
public void writeToParcel(Parcel parcel,int flags) {
parcel.writeString(mFileName);
parcel.writeInt(mMediaDataSize);
parcel.writeByteArray(mMediaDataArray);
}
數組寫入方式是調用writeByteArray寫入數據。在onTransact中有處理TRANSACTION_onMediaSharing:
case TRANSACTION_onMediaSharing:
{
data.enforceInterface(descriptor);
com.cloudyhill.mediashare.MediaData _arg0;
if ((0!=data.readInt())) {
// 這裏的data就是之前要往裏寫入的數據_data
_arg0 = com.cloudyhill.mediashare.MediaData.CREATOR.createFromParcel(data);
} else {
_arg0 =null;
}
this.onMediaSharing(_arg0);
reply.writeNoException();
return true;
}
從MediaData的用data數據即寫入的數據,調用MediaData的createFromParcel創建一個MediaData對象:
public static final CreatorCREATOR =new Creator() {
@Override
public MediaData createFromParcel(Parcel in) {
return new MediaData(in);
}
};
protected MediaData(Parcel in) {
readFromParcel(in);
}
public void readFromParcel(Parcel reply) {
mFileName = reply.readString();
mMediaDataSize = reply.readInt();
mMediaDataArray = reply.createByteArray();
}
這樣就把Parcelable數據從Client端傳給Server端,這個時候Server端的onMediaSharing中調用onMediaSharing,就能得到Client端的數據了。
上面還留了一個坑,爲什麼說mRemote即Server端的IMediaShareInterface?我們注意到Server端的Service有個接口:
public IBinder onBind(Intent intent) {
Log.d(TAG,"<onBind>");
return mIMediaShareMgr;
}
然後,看Client端獲取IMediaDataInterface的方法,下面這個service就是bindService建立連接以後返回的Server端的mIMediaShareMgr,跟蹤一下它的走向:
mIMediaShare = IMediaShareInterface.Stub.asInterface(service);
public static com.cloudyhill.mediashare.IMediaShareInterface asInterface(android.os.IBinder obj)
{
if ((obj==null)) {
return null;
}
android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
if (((iin!=null)&&(iininstanceof com.cloudyhill.mediashare.IMediaShareInterface))) {
return ((com.cloudyhill.mediashare.IMediaShareInterface)iin);
}
return new com.cloudyhill.mediashare.IMediaShareInterface.Stub.Proxy(obj);
}
Proxy(android.os.IBinder remote) {
mRemote = remote;
}
最終傳給了mRemote,即mRemote就是Server端的mIMediaShareMgr。
6、踩坑記錄
6.1 錯誤提示:ProcessException: Error while executing process D:\android\sdk\build-tools\28.0.3\aidl.exe with arguments
基本數據類型的數組(例如byte[])不能直接作爲aidl接口參數傳遞,要用實現Parcelable的數據類型來封裝數組。也就是說,aidl支持參數傳遞常用的數據類型byte、int等,但是並不直接支持byte[]、int[]等數組類型。也就是需要用Parcelable來序列化數據。
接口中傳遞的封裝數據類型,需要添加一個aidl文件,以parcelable來聲明該類型,在引用該類型的aidl文件中加import引用,並實現該類型的實現。詳情可參考5.1部分。
6.2 aidl文件的package name和Parcelable實現類的package name不一致,也會提示6.1的錯誤,應該是找不到實現類,所以報錯。
6.3 aidl文件中聲明數據流向是out或者inout,但是server端沒有實現readFromParcel。看aidl編譯生成的java文件,和數據流向有關的函數接口實現:
@Override public void onMediaSharing(com.cloudyhill.mediashare.MediaData data) throws android.os.RemoteException {
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
try {
_data.writeInterfaceToken(DESCRIPTOR);
mRemote.transact(Stub.TRANSACTION_onMediaSharing, _data, _reply, 0);
_reply.readException();
if ((0!=_reply.readInt())) {
data.readFromParcel(_reply);
}
} finally {
_reply.recycle();
_data.recycle();
}
}
從這裏看,數據流向聲明爲out、inout需要複寫readFromParcel。
6.4 Binder通信大小限制
Binder通信大小限制爲1M – 8KB,除非定製化Binder通信大小。在android源碼中ProcessState.cpp中有配置信息:
#define BINDER_VM_SIZE((1*1024*1024) - (4096 *2))
但是我設置爲512*1024KB,同樣會報TransactionTooLargeException的錯誤,因此,本例中設置byte[] data = new byte[256*1024],一次256KB。原因可以參考以下知乎上的回答:
“Binder的線程池數量默認是15個,由15個線程共享這1MB-8KB的內存空間,所以實際傳輸大小並沒有那麼大。”
抱着嚴謹的態度,這種說法正確與否還有待驗證。
源碼請另外參考附件demo程序,Client App和Server App。
參考鏈接:
https://www.zhihu.com/question/39440766/answer/89210950
https://www.jianshu.com/p/533de5fa6e4c
http://gityuan.com/2015/10/31/binder-prepare/
https://blog.csdn.net/luoyanglizi/article/details/51980630
https://blog.csdn.net/luoyanglizi/article/details/51958091