AIDL的作用
通過代碼來實現這個數據傳輸過程是冗長乏味的,Android提供了AIDL工具來處理這項工作。
AIDL IPC機制是面向接口的,像COM或Corba一樣,但是更加輕量級。它是使用代理類在客戶端和實現端傳遞數據。
- Calls made from the local process are executed in the same thread that is making the call. If this is your main UI thread, that thread continues to execute in the AIDL interface. If it is another thread, that is the one that executes your code in the service. Thus, if only local threads are accessing the service, you can completely control which threads are executing in it (but if that is the case, then you shouldn't be using AIDL at all, but should instead create the interface by implementing a Binder).
- Calls from a remote process are dispatched from a thread pool the platform maintains inside of your own process. You must be prepared for incoming calls from unknown threads, with multiple calls happening at the same time. In other words, an implementation of an AIDL interface must be completely thread-safe.
- The
oneway
keyword modifies the behavior of remote calls. When used, a remote call does not block; it simply sends the transaction data and immediately returns. The implementation of the interface eventually receives this as a regular call from theBinder
thread pool as a normal remote call. Ifoneway
is used with a local call, there is no impact and the call is still synchronous.
AIDL使用簡單的語法來聲明接口,描述其方法以及方法的參數和返回值。這些參數和返回值可以是任何類型,甚至是其他AIDL生成的接口。
需要特別注意的是,對於非基本數據類型,也不是String和CharSequence類型的,需要有方向指示,包括in、out和inout,in表示由客戶端設置,out表示由服務端設置,inout是兩者均可設置。
import com.demo.Person;
interface IMyService {
void savePersonInfo(in Person person);
List<Person> getAllPerson();
}
private LinkedList<Person> personList = new LinkedList<Person>();
@Override
public IBinder onBind(Intent intent) {
return mBinder;
}
private final IMyService.Stub mBinder = new IMyService.Stub(){
@Override
public void savePersonInfo(Person person) throws RemoteException {
if (person != null){
personList.add(person);
}
}
@Override
public List<Person> getAllPerson() throws RemoteException {
return personList;
}
};
}
public static abstract class Stub extends android.os.Binder implements com.demo.IMyService
1) void writeToParcel(Parcel dest, int flags) 將需要序列化存儲的數據寫入外部提供的Parcel對象dest。而看了網上的代碼例子,個人猜測,讀取Parcel數據的次序要和這裏的write次序一致,否則可能會讀錯數據。具體情況我沒試驗過!
2) describeContents() 沒搞懂有什麼用,反正直接返回0也可以
3) static final Parcelable.Creator對象CREATOR 這個CREATOR命名是固定的,而它對應的接口有兩個方法:
createFromParcel(Parcel source) 實現從source創建出JavaBean實例的功能
newArray(int size) 創建一個類型爲T,長度爲size的數組,僅一句話(return new T[size])即可。估計本方法是供外部類反序列化本類數組使用。
private String name;
private String telNumber;
private int age;
public Person() {}
public Person(Parcel pl){
name = pl.readString();
telNumber = pl.readString();
age = pl.readInt();
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getTelNumber() {
return telNumber;
}
public void setTelNumber(String telNumber) {
this.telNumber = telNumber;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(name);
dest.writeString(telNumber);
dest.writeInt(age);
}
public static final Parcelable.Creator<Person> CREATOR = new Parcelable.Creator<Person>() {
@Override
public Person createFromParcel(Parcel source) {
return new Person(source);
}
@Override
public Person[] newArray(int size) {
return new Person[size];
}
};
}
然後創建Person.aidl文件,注意這裏的parcelable和原來實現的Parcelable 接口,開頭的字母p一個小寫一個大寫:
parcelable Person;
3. 拋出的異常是不能返回給調用者(跨進程拋異常處理是不可取的)。
3. 客戶端獲取接口
private ServiceConnection mRemoteConnection = new ServiceConnection() {
public void onServiceConnected(ComponentName className, IBinder service) {
mRemoteService = IMyService.Stub.asInterface(service);
}
public void onServiceDisconnected(ComponentName className) {
mRemoteService = null;
}
};
* Cast an IBinder object into an com.demo.IMyService interface,
* generating a proxy if needed.
*/
public static com.demo.IMyService asInterface(android.os.IBinder obj) {...}
unbindService(mRemoteConnection);
}else{
bindService(new Intent("com.demo.IMyService"),
mRemoteConnection, Context.BIND_AUTO_CREATE);
}
mIsRemoteBound = !mIsRemoteBound;
new View.OnClickListener(){
private int index = 0;
@Override
public void onClick(View view) {
Person person = new Person();
index = index + 1;
person.setName("Person" + index);
person.setAge(20);
person.setTelNumber("123456");
try {
mRemoteService.savePersonInfo(person);
} catch (RemoteException e) {
e.printStackTrace();
}
}
});
listPersonButton.setOnClickListener(
new View.OnClickListener(){
@Override
public void onClick(View view) {
List<Person> list = null;
try {
list = mRemoteService.getAllPerson();
} catch (RemoteException e) {
e.printStackTrace();
}
if (list != null){
StringBuilder text = new StringBuilder();
for(Person person : list){
text.append("\nPerson name:");
text.append(person.getName());
text.append("\n age :");
text.append(person.getAge());
text.append("\n tel number:");
text.append(person.getTelNumber());
}
inputPersonEdit.setText(text);
}else {
Toast.makeText(ServiceActivity.this, "get data error",
Toast.LENGTH_SHORT).show();
}
}
});
Permission權限
如果Service在AndroidManifest.xml中聲明瞭全局的強制的訪問權限,其他引用必須聲明權限才能來start,stop或bind這個service.
另外,service可以通過權限來保護她的IPC方法調用,通過調用checkCallingPermission(String)方法來確保可以執行這個操作。
AndroidManifest.xml的Service元素
<intent-filter>
<action android:name="com.demo.IMyService" />
</intent-filter>
</service>
The name of the process where the service is to run. Normally, all components of an application run in the default process created for the application. It has the same name as the application package. The <application> element's process attribute can set a different default for all components. But component can override the default with its own process attribute, allowing you to spread your application across multiple processes.