【Android基础知识】AIDL跨进程调用

AIDL（Android interface definition language）Android接口定义语言。

Android 系统中，各应用程序都运行在自己的进程中，进程之间一般无法直接进行数据交换，为了实现这种跨进程通信，Android提供了AIDL Service.

        客户端访问Service时，Android并不是直接返回Service对象给客户端，只是将Service的代理（IBinder对象）通过onBind方法返回给客户端。因此Android的AIDL的远程接口的实现类就是那个IBinder实现类。

和绑定本地Service不同的是，本地会把IBinder对象本身返回给onServiceConnected方法的第二个参数。但是远程Service只是将IBinder对象的代理传给客户端ServiceConnected的第二个参数。当客户端获取了远程Service的IBinder对象的代理之后，接下来就可以通过IBinder对象去回调远程Service的属性或方法了。

AIDL使用实例：实现服务器端启动一个服务，随机更改颜色和体重，客户端获取这些信息

服务器端

1.建立aidl文件

package com.aidl;
interface ICat
{
String getColor();
double getWeight();
}

2.android会自动生成一个类，类里有stub静态内部类实现了IBinder和Aidl接口。

/*
* This file is auto-generated.  DO NOT MODIFY.
* Original file: E:\\AIDLService\\src\\com\\aidl\\ICat.aidl
*/
package com.aidl;
public interface ICat extends android.os.IInterface
{
/** Local-side IPC implementation stub class. */
public static abstract class Stub extends android.os.Binder implements com.aidl.ICat
{
private static final java.lang.String DESCRIPTOR = "com.aidl.ICat";
/** Construct the stub at attach it to the interface. */
public Stub()
{
this.attachInterface(this, DESCRIPTOR);
}
/**
* Cast an IBinder object into an com.aidl.ICat interface,
* generating a proxy if needed.
*/
public static com.aidl.ICat asInterface(android.os.IBinder obj)
{
if ((obj==null)) {
return null;
}
android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
if (((iin!=null)&&(iin instanceof com.aidl.ICat))) {
return ((com.aidl.ICat)iin);
}
return new com.aidl.ICat.Stub.Proxy(obj);
}
@Override public android.os.IBinder asBinder()
{
return this;
}
@Override public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException
{
switch (code)
{
case INTERFACE_TRANSACTION:
{
reply.writeString(DESCRIPTOR);
return true;
}
case TRANSACTION_getColor:
{
data.enforceInterface(DESCRIPTOR);
java.lang.String _result = this.getColor();
reply.writeNoException();
reply.writeString(_result);
return true;
}
case TRANSACTION_getWeight:
{
data.enforceInterface(DESCRIPTOR);
double _result = this.getWeight();
reply.writeNoException();
reply.writeDouble(_result);
return true;
}
}
return super.onTransact(code, data, reply, flags);
}
private static class Proxy implements com.aidl.ICat
{
private android.os.IBinder mRemote;
Proxy(android.os.IBinder remote)
{
mRemote = remote;
}
@Override public android.os.IBinder asBinder()
{
return mRemote;
}
public java.lang.String getInterfaceDescriptor()
{
return DESCRIPTOR;
}
@Override public java.lang.String getColor() throws android.os.RemoteException
{
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
java.lang.String _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
mRemote.transact(Stub.TRANSACTION_getColor, _data, _reply, 0);
_reply.readException();
_result = _reply.readString();
}
finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
@Override public double getWeight() throws android.os.RemoteException
{
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
double _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
mRemote.transact(Stub.TRANSACTION_getWeight, _data, _reply, 0);
_reply.readException();
_result = _reply.readDouble();
}
finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
}
static final int TRANSACTION_getColor = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
static final int TRANSACTION_getWeight = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);
}
public java.lang.String getColor() throws android.os.RemoteException;
public double getWeight() throws android.os.RemoteException;
}

3.创建我们自己的Service，实现stub类，返回IBinder对象。

/*
* 定义到AIDL接口之后，需要定义一个Service实现类，该Service的onBind方法
* 所返回的IBinder对象时ADT所生成的ICat.stub的子类的实例。
*/
public class AidlService extends Service{

private CatBinder catBinder;
Timer timer = new Timer();
String[] colors = new String[]{
"红色",
"黄色",
"黑色"
};
double [] weights = new double[]{
2.3,
3.1,
1.58
};
private String color;
private double weight;
//继承Stub,也就是实现了ICat接口，并实现了IBinder接口
public class CatBinder extends Stub{

@Override
public String getColor() throws RemoteException {
// TODO Auto-generated method stub
return color;
}
@Override
public double getWeight() throws RemoteException {
// TODO Auto-generated method stub
return weight;
}
}

@Override
public void onCreate() {
// TODO Auto-generated method stub
super.onCreate();
catBinder = new CatBinder();
timer.schedule(new TimerTask() {

@Override
public void run() {
// TODO Auto-generated method stub
//随机的改变Service组件内color、weight的属性的值
int rand = (int)(Math.random()*3);
color = colors[rand];
weight = weights[rand];
}
}, 0,800);
}

@Override
public void onDestroy() {
// TODO Auto-generated method stub
timer.cancel();
}

@Override
public IBinder onBind(Intent intent) {
// TODO Auto-generated method stub
/*
* 返回catBinder对象，绑定本地，直接传递对象
* 绑定远程，传递代理。
*/
return catBinder;
}

}

4.创建客户端程序，创建aidl接口文件，注意文件名和包名要完全相同，同样自动生成一个类。

5.绑定service，获取代理。

public class MainActivity extends Activity {

private ICat catService;
private Button get;
EditText color,weight;

private ServiceConnection connection = new ServiceConnection() {

@Override
public void onServiceDisconnected(ComponentName name) {
// TODO Auto-generated method stub
catService = null;
}

@Override
public void onServiceConnected(ComponentName name, IBinder service) {
// TODO Auto-generated method stub
//获取远程Service的onBind方法返回的对象的代理
catService = ICat.Stub.asInterface(service);
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(save
db37
dInstanceState);
setContentView(R.layout.activity_main);
get = (Button)findViewById(R.id.button1);
color = (EditText)findViewById(R.id.editText1);
weight = (EditText)findViewById(R.id.editText2);

//创建所需绑定的Service的intent
Intent intent = new Intent();
intent.setAction("com.aidl.AIDL_Service");
Intent eintent = new Intent(getExplicitIntent(getBaseContext(),intent));
//绑定远程Service
bindService(eintent, connection, Service.BIND_AUTO_CREATE);

get.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
try{
color.setText(catService.getColor());
weight.setText(catService.getWeight()+"");
}catch(RemoteException e){
e.printStackTrace();
}
}
});
}
//将隐式intent装换为显示intent
public static Intent getExplicitIntent(Context context, Intent implicitIntent) {
// Retrieve all services that can match the given intent
PackageManager pm = context.getPackageManager();
List<ResolveInfo> resolveInfo = pm.queryIntentServices(implicitIntent, 0);
// Make sure only one match was found
if (resolveInfo == null || resolveInfo.size() != 1) {
return null;
}
// Get component info and create ComponentName
ResolveInfo serviceInfo = resolveInfo.get(0);
String packageName = serviceInfo.serviceInfo.packageName;
String className = serviceInfo.serviceInfo.name;
ComponentName component = new ComponentName(packageName, className);
// Create a new intent. Use the old one for extras and such reuse
Intent explicitIntent = new Intent(implicitIntent);
// Set the component to be explicit
explicitIntent.setComponent(component);
return explicitIntent;
}

@Override
protected void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
this.unbindService(connection);
}
}

AIDL默认支持的数据类型

基本数据类型（除short）

String、CharSequence、List、Map、Parcelable（序列化）

Android5.0 以后Service不能隐式启动，service Intent must be explitict

源码中是这样的 （源码位置：sdk/sources/android-21/android/app/ContextImpl.java）

private void validateServiceIntent(Intent service) {
if (service.getComponent() == null && service.getPackage() == null) {
if (getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.LOLLIPOP) {
IllegalArgumentException ex = new IllegalArgumentException(
"Service Intent must be explicit: " + service);
throw ex;
} else {
Log.w(TAG, "Implicit intents with startService are not safe: " + service
+ " " + Debug.getCallers(2, 3));
}
}
}

有两种解决方式：

1.设置package和packagename

Intent mIntent = new Intent();
mIntent.setAction("XXX.XXX.XXX");//你定义的service的action
mIntent.setPackage(getPackageName());//这里你需要设置你应用的包名
context.startService(mIntent);

2.将隐式转换为显式启动

public static Intent getExplicitIntent(Context context, Intent implicitIntent) {
// Retrieve all services that can match the given intent
PackageManager pm = context.getPackageManager();
List<ResolveInfo> resolveInfo = pm.queryIntentServices(implicitIntent, 0);
// Make sure only one match was found
if (resolveInfo == null || resolveInfo.size() != 1) {
return null;
}
// Get component info and create ComponentName
ResolveInfo serviceInfo = resolveInfo.get(0);
String packageName = serviceInfo.serviceInfo.packageName;
String className = serviceInfo.serviceInfo.name;
ComponentName component = new ComponentName(packageName, className);
// Create a new intent. Use the old one for extras and such reuse
Intent explicitIntent = new Intent(implicitIntent);
// Set the component to be explicit
explicitIntent.setComponent(component);
return explicitIntent;
}

Aidl的底层实现原理



1.首先Servier去实现了Stub（Binder）内部类，实现了里面的方法并返回一个IBinder对象。

2.客户端调用Stub.asInterface(Binder)，这里其实返回的是代理类Proxy对象 return new com.aidl.ICat.Stub.Proxy(obj)，该方法代码如下：

public static com.aidl.ICat asInterface(android.os.IBinder obj)
{
if ((obj==null)) {
return null;
}
android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
if (((iin!=null)&&(iin instanceof com.aidl.ICat))) {
return ((com.aidl.ICat)iin);
}
return new com.aidl.ICat.Stub.Proxy(obj);
}

Proxy（IBinder代理类代码如下）里面实现了我们接口中定义的两个方法，getColor和getWeight

private static class Proxy implements com.aidl.ICat
{
private android.os.IBinder mRemote;
Proxy(android.os.IBinder remote)
{
mRemote = remote;
}
@Override public android.os.IBinder asBinder()
{
return mRemote;
}
public java.lang.String getInterfaceDescriptor()
{
return DESCRIPTOR;
}
@Override public java.lang.String getColor() throws android.os.RemoteException
{
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
java.lang.String _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
mRemote.transact(Stub.TRANSACTION_getColor, _data, _reply, 0);
_reply.readException();
_result = _reply.readString();
}
finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
@Override public double getWeight() throws android.os.RemoteException
{
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
double _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
mRemote.transact(Stub.TRANSACTION_getWeight, _data, _reply, 0);
_reply.readException();
_result = _reply.readDouble();
}
finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
}
static final int TRANSACTION_getColor = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
static final int TRANSACTION_getWeight = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);
}

3.客户端利用代理对象Proxy 调用了getColor（）方法，Proxy类实现的getColor（）方法，该方法会把我们调用的方法的ID Stub.TRANSACTION_getColor 传递给底层IPC

mRemote.transact(Stub.TRANSACTION_getColor, _data, _reply, 0);

4.到达服务器端调用onTransact方法，该方法会根据刚才传入的方法ID通过switch case 去匹配到TRANSACTION_getColor ，然后会调用 this.getColor()方法，这里的this就

是Stub类对象，我们的Service中 继承了Stub类并且实现了里面的方法，这里方法会被回调this.getColor()，把结果发送给客户端。

public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException
{
switch (code)
{
case INTERFACE_TRANSACTION:
{
reply.writeString(DESCRIPTOR);
return true;
}
case TRANSACTION_getColor:
{
data.enforceInterface(DESCRIPTOR);
java.lang.String _result = this.getColor();
reply.writeNoException();
reply.writeString(_result);
return true;
}
case TRANSACTION_getWeight:
{
data.enforceInterface(DESCRIPTOR);
double _result = this.getWeight();
reply.writeNoException();
reply.writeDouble(_result);
return true;
}
}
return super.onTransact(code, data, reply, flags);
}