提到的進程間通信(IPC:Inter-Process Communication),在Android系統中,一個進程是不能直接訪問另一個進程的內存的,需要提供一些機制在不同的進程之間進行通信,Android官方推出了AIDL(Android Interface Definition Language),它是基於Binder機制的,至於官方為什麼要採用Binder,查看為什麼Android要採用Binder作為IPC機制,分析很全面。
上篇Android之Service總結 提到組件在與Service通信方法有三種。
後面兩種可以跨進程通信,是基於Binder機制的通信方式。
在確定使用什麼機制之前,首先了解應用場景。Android系統中,如果組件與服務通信是在同一進程,就使用第一種方式;如果是跨進程通信,使用第二種和第三種,兩者不同在於,Messenger不能處理多線程併發請求。
AIDL是可以處理多線程訪問的請求的,所以實現AIDL首先要保證線程安全。
onBind()
,返回Stub類的實現在Android Studio中工程目錄下,反鍵new -> AIDL -> AIDL FIle
,可以新建aidl文件,編譯器會自動在app(殼工程)/src/main/
目錄下新建aidl文件,同時也會新建文件夾,默認以工程包名作為aidl文件所在的目錄。
目錄結構如下:
也可以手動創建,aidl接口定義的包名也可以和工程包名不同,aidl文件語法和Java語法相似,aidl定義的接口名必須和文件名一致,而且支持傳遞自定義的數據類型,需要實現parcelable接口。
IRemoteService.aidl
package com.demo.aidl;
import com.demo.aidl.ParcelableData;
interface IRemoteService {
/**
* 獲取當前進程的pid
/
int getPid();
/*
* 獲取當前服務名稱
/
String getServiceName();
/*
* 處理客戶端傳過來的數據
*/
void handleData(in ParcelableData data);
}
ParcelableData.aidl
package com.demo.aidl;
/**
- 聲明支持傳遞的類
*/
parcelable ParcelableData;
IRemoteServiceCallBack.aidl
package com.demo.aidl;
oneway interface IRemoteServiceCallBack {
void valueChanged(int value);
}
aidl文件定義的接口支持的數據類型如下:
aidl文件中定義的方法接受的參數,除了Java的基本數據類型和aidl定義的接口之外,其他參數都需要標記數據的走向,in/out/inout,基本數據類型和aidl定義的接口作為參數,默認是in。
關鍵字oneway
表示用戶請求相應功能時不需要等待響應可直接調用返回,非阻塞效果,該關鍵字可以用來聲明接口或者聲明方法,如果接口聲明中用到了oneway關鍵字,則該接口聲明的所有方法都採用oneway方式
新建完畢aidl文件後,rebuild工程或者使用gradle assembleDebug(或gradle assembleRelease)指令編譯工程,生成具體的java代碼,在殼工程/build/generated/aidl/
目錄下的debug
或者release
文件夾下,根據build的類型而定,如圖:
AIDL接口首次公佈後對其的任何修改都必須保持向後兼容性,避免中斷客戶端對服務的使用,因為需要將.aidl文件複製給其他應用,才能使其他應用能夠訪問服務,所以必須保持對原始接口的支持。
Android SDK會根據.aidl文件生成同名.java文件,生成的接口中有一個Stub的抽象子類,這個類實現(implements)aidl定義的接口,同時繼承了Binder
。
具體代碼如下:
private final IRemoteService.Stub mBinder = new IRemoteService.Stub() {
@Override
public int getPid() throws RemoteException {
return Process.myPid();
}
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> <span class="hljs-function">String <span class="hljs-title">getServiceName</span><span class="hljs-params">()</span> <span class="hljs-keyword">throws</span> RemoteException </span>{
<span class="hljs-keyword">return</span> RemoteService.<span class="hljs-keyword">this</span>.getClass().getSimpleName();
}
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">handleData</span><span class="hljs-params">(ParcelableData data)</span> <span class="hljs-keyword">throws</span> RemoteException </span>{
Toast.makeText(RemoteService.<span class="hljs-keyword">this</span>, <span class="hljs-string">"num is "</span> + data.num, Toast.LENGTH_SHORT).show();
}
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">registerCallback</span><span class="hljs-params">(IRemoteServiceCallBack cb)</span> <span class="hljs-keyword">throws</span> RemoteException </span>{
<span class="hljs-keyword">if</span>(cb != <span class="hljs-keyword">null</span>) {
mCallBacks.register(cb);
}
}
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">unregisterCallback</span><span class="hljs-params">(IRemoteServiceCallBack cb)</span> <span class="hljs-keyword">throws</span> RemoteException </span>{
<span class="hljs-keyword">if</span>(cb != <span class="hljs-keyword">null</span>) {
mCallBacks.unregister(cb);
}
}
};
現在mBinder是Stub類的一個實例,同時也是一個Binder,用於服務定義的RPC服務,作為onBind()
方法的返回對象實例。
實現AIDL接口注意事項:
實現接口後,需要向客戶端將接口暴露出來,以便客戶端使用。將Stub的實例化對象作為Service中onBind()
方法的返回對象。
public class RemoteService extends Service {
/**
* 回調容器
*/
private final RemoteCallbackList<IRemoteServiceCallBack> mCallBacks = new RemoteCallbackList<>();
/**
* aidl接口具體實現
*/
private final IRemoteService.Stub mBinder = new IRemoteService.Stub() {
@Override
public int getPid() throws RemoteException {
return Process.myPid();
}
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> <span class="hljs-function">String <span class="hljs-title">getServiceName</span><span class="hljs-params">()</span> <span class="hljs-keyword">throws</span> RemoteException </span>{
<span class="hljs-keyword">return</span> RemoteService.<span class="hljs-keyword">this</span>.getClass().getSimpleName();
}
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">handleData</span><span class="hljs-params">(ParcelableData data)</span> <span class="hljs-keyword">throws</span> RemoteException </span>{
Toast.makeText(RemoteService.<span class="hljs-keyword">this</span>, <span class="hljs-string">"num is "</span> + data.num, Toast.LENGTH_SHORT).show();
}
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">registerCallback</span><span class="hljs-params">(IRemoteServiceCallBack cb)</span> <span class="hljs-keyword">throws</span> RemoteException </span>{
<span class="hljs-keyword">if</span>(cb != <span class="hljs-keyword">null</span>) {
mCallBacks.register(cb);
}
}
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">unregisterCallback</span><span class="hljs-params">(IRemoteServiceCallBack cb)</span> <span class="hljs-keyword">throws</span> RemoteException </span>{
<span class="hljs-keyword">if</span>(cb != <span class="hljs-keyword">null</span>) {
mCallBacks.unregister(cb);
}
}
};
<span class="hljs-meta">@Nullable</span>
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> <span class="hljs-function">IBinder <span class="hljs-title">onBind</span><span class="hljs-params">(Intent intent)</span> </span>{
<span class="hljs-keyword">return</span> mBinder;
}
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">onDestroy</span><span class="hljs-params">()</span> </span>{
<span class="hljs-comment">// 註銷所有回調</span>
mCallBacks.kill();
}
}
服務提供給第三方應用使用,其他應用就必須要有接口類,在客戶端創建相同的aidl文件(可以直接拷貝過去)。
核心連接遠端服務的代碼:
/**
* 遠端服務
*/
private IRemoteService mService;
private ServiceConnection mConnection = new ServiceConnection() {
/**
* 連接服務器成功回調
*
* @param className
* @param service
*/
public void onServiceConnected(ComponentName className, IBinder service) {
mService = IRemoteService.Stub.asInterface(service);
}
<span class="hljs-comment">/**
* 服務器因為一場情況斷開連接時候回調
*
* @param className
*/</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onServiceDisconnected</span>(<span class="hljs-params">ComponentName className</span>) </span>{
mService = <span class="hljs-literal">null</span>;
}
};
/**
- 綁定服務
*/
private void doBindService() {
isBound = true;
Intent intent = new Intent(BindRemoteServiceActivity.this, RemoteService.class);
bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
}
/**
-
解除綁定
*/
private void doUnbindService() {
if(isBound && mService != null) {
isBound = false;
try {
mService.unregisterCallback(mCallback);
} catch (RemoteException e) {
e.printStackTrace();
}
unbindService(mConnection);
}
}
/**
- 向服務端發送信息
*/
private void doSendMsg() {
if(!isBound || mService == null) {
return;
}
ParcelableData data = new ParcelableData(1);
try {
mService.handleData(data);
} catch (RemoteException e) {
e.printStackTrace();
}
}
/**
-
調用服務端方法獲取信息
*/
private void doGetServiceInfo() {
if(!isBound || mService == null) {
return;
}
try {
String info = mService.getServiceName();
mInfoTv.setText(<span class="hljs-string">"Service info :"</span> + info);
} catch (RemoteException e) {
e.printStackTrace();
}
}
詳情代碼貼上來比較長,貼上工程地址,點我呀!!!
Messenger的使用相對於AIDL方便好多,因為Messenger是Android系統中自帶的類,服務端和客戶端都不用創建AIDL文件。
Messenger會持有一個Handler,這個Handler用於處理接受到的信息,在服務端和乘客通過Messenger實現雙方通信。
代碼實例:
public class MessengerService extends Service {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> MSG_REGISTER_CLIENT = <span class="hljs-number">0X001</span>;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> MSG_UNREGISTER_CLIENT = <span class="hljs-number">0X010</span>;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> MSG_HANDLE = <span class="hljs-number">0X100</span>;
<span class="hljs-keyword">private</span> ArrayList<Messenger> mClients = <span class="hljs-keyword">new</span> ArrayList<>();
<span class="hljs-keyword">private</span> <span class="hljs-keyword">final</span> Messenger mMessenger = <span class="hljs-keyword">new</span> Messenger(<span class="hljs-keyword">new</span> IncomingHandler());
<span class="hljs-meta">@Nullable</span>
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> <span class="hljs-function">IBinder <span class="hljs-title">onBind</span><span class="hljs-params">(Intent intent)</span> </span>{
<span class="hljs-function"><span class="hljs-keyword">return</span> mMessenger.<span class="hljs-title">getBinder</span><span class="hljs-params">()</span></span>;
}
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">onDestroy</span><span class="hljs-params">()</span> </span>{
Toast.makeText(<span class="hljs-keyword">this</span>, <span class="hljs-string">"Remote Service Destroy"</span>, Toast.LENGTH_SHORT).show();
}
<span class="hljs-keyword">private</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">IncomingHandler</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">Handler</span> </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">handleMessage</span><span class="hljs-params">(Message msg)</span> </span>{
<span class="hljs-keyword">switch</span> (msg.what) {
<span class="hljs-keyword">case</span> MSG_REGISTER_CLIENT:
mClients.add(msg.replyTo);
<span class="hljs-keyword">break</span>;
<span class="hljs-keyword">case</span> MSG_UNREGISTER_CLIENT:
mClients.remove(msg.replyTo);
<span class="hljs-keyword">break</span>;
<span class="hljs-keyword">case</span> MSG_HANDLE:
<span class="hljs-keyword">for</span> (Messenger mClient : mClients) {
<span class="hljs-keyword">try</span> {
mClient.send(Message.obtain(<span class="hljs-keyword">null</span>, MSG_HANDLE, msg.arg1, <span class="hljs-number">0</span>));
} <span class="hljs-keyword">catch</span> (RemoteException e) {
e.printStackTrace();
mClients.remove(mClient);
}
}
<span class="hljs-keyword">break</span>;
<span class="hljs-keyword">default</span>:
<span class="hljs-keyword">super</span>.handleMessage(msg);
}
}
};
}
核心代碼:
/**
* 關聯遠端服務的messenger
*/
private Messenger mServiceWrapper;
/**
* 用於處理服務端發送的信息
*/
final Messenger mMessenger = new Messenger(new IncomingHandler());
private ServiceConnection mConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
mServiceWrapper = new Messenger(service);
mInfoTv.setText(<span class="hljs-string">"Connected Service"</span>);
<span class="hljs-keyword">try</span> {
<span class="hljs-comment">// 添加監聽註冊</span>
Message msg = Message.obtain(<span class="hljs-literal">null</span>, MessengerService.MSG_REGISTER_CLIENT);
msg.replyTo = mMessenger;
mServiceWrapper.send(msg);
} <span class="hljs-keyword">catch</span> (RemoteException e) {
e.printStackTrace();
}
}
@<span class="hljs-function">Override
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onServiceDisconnected</span>(<span class="hljs-params">ComponentName name</span>) </span>{
mServiceWrapper = <span class="hljs-literal">null</span>;
mInfoTv.setText(<span class="hljs-string">"Disconnected"</span>);
}
};
/**
-
綁定服務
*/
private void doBindService() {
if(!isBound) {
bindService(new Intent(this, MessengerService.class), mConnection, Context.BIND_AUTO_CREATE);
isBound = <span class="hljs-literal">true</span>;
mInfoTv.setText(<span class="hljs-string">"Binding..."</span>);
}
}
/**
-
移除監聽並解綁服務
*/
private void doUnbindService() {
if(isBound) {
if(mServiceWrapper != null) {
try {
Message msg = Message.obtain(null, MessengerService.MSG_UNREGISTER_CLIENT);
msg.replyTo = mMessenger;
mServiceWrapper.send(msg);
} catch (RemoteException e) {
e.printStackTrace();
}
}
unbindService(mConnection);
isBound = <span class="hljs-literal">false</span>;
mInfoTv.setText(<span class="hljs-string">"Unbinding..."</span>);
}
}
/**
- 向服務端發送信息
*/
private void doSendMsg() {
if(mServiceWrapper != null) {
try {
Message msg = Message.obtain(null,
MessengerService.MSG_HANDLE, this.hashCode(), 0);
mServiceWrapper.send(msg);
} catch (RemoteException e) {
e.printStackTrace();
}
}
}
使用Messenger向服務端發送信息,使用的是Messenger.send(Message)
方法,這個方法具體實現如下:
public void send(Message message) throws RemoteException {
mTarget.send(message);
}
方法內部調用mTarget.send(Message)
方法,在Messenger中,mTarget
是在構造方法裡面被賦值的,有兩個構造函數。
public Messenger(Handler target) {
mTarget = target.getIMessenger();
}
public Messenger(IBinder target) {
mTarget = IMessenger.Stub.asInterface(target);
}
第一個構造函數好理解,mTarget.send(Message)
實際上是將Message
加入了構造函數傳入的Handler的消息隊列,Demo工程中服務端向乘客端發送信息就是使用的這種方法
第二個構造函數是不是很眼熟,這不就是獲取AIDL定義的接口嘛!!!轉了一圈回到了上面的AIDL,客戶端向服務端發送信息實際上還是通過AIDL,只不過Android系統幫我們做了一層封裝。
到此,從Android之Service總結到Android中常用的進程通信都已經總結完畢,算是2016的一個完結,撒花!!
最後附上Demo工程地址:https://github.com/Kyogirante/AIDLDemo
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