Foreword

I [003] AIDL AIDL what is described, but it seems to have friends do not understand ask me, I'll write a final version of the article, so you ten minutes to completely understand AIDL, the following code are all handwritten.

aims

Server process to sign up for a service Binder SM, the Binder service provides two interfaces: add and minus
proxy class BinderProxy Client service through the process of obtaining Binder SM, and calls the two interfaces add, minus

1 no AIDL world

1.1 Server Process

    class CommandBinder extends Binder {
        @Override
        protected boolean onTransact(int code, @NonNull Parcel data, @Nullable Parcel reply, int flags) throws RemoteException {
            if (code == 1) {
                int a = data.readInt();
                int b = data.readInt();
                reply.writeInt(a + b);
                return true;
            } else if (code == 2) {
                int a = data.readInt();
                int b = data.readInt();
                reply.writeInt(a + b);
                return true;
            }
            return super.onTransact(code, data, reply, flags);
        }
    }

    void main() {
        //注册binder服务
        ServiceManager.addService("command", new CommandBinder());
    }

1.2 Client Process

    int add(int a, int b) {
        int code = 1;
        BinderProxy mClient = ServiceManager.getService("command");
        Parcel data = Parcel.obtain();
        data.writeInt(a);
        data.writeInt(b);
        Parcel reply = Parcel.obtain();
        mClient.transact(code, data, reply, 0);//flag设置成0,调用这个方法会跨进程调用Binder服务类中onTransact方法
        int result = reply.readInt();
        return result;
    }

    int minus(int a, int b) {
        int code = 2;
        BinderProxy mClient = ServiceManager.getService("command");
        Parcel data = Parcel.obtain();
        data.writeInt(a);
        data.writeInt(b);
        Parcel reply = Parcel.obtain();
        mClient.transact(code, data, reply, 0);//flag设置成0,调用这个方法会跨进程调用Binder服务类中onTransact方法
        int result = reply.readInt();
        return result;
    }

There are 2 AIDL world

AIDL file

    //aidl
    interface ICommand {
        int add(int a, int b);
        int minus(int a, int b);
    }

2.1 Server Process

Compared to 1.1 in the code, we find that we are not the direct successor Binder, but inherited aidl file is automatically generated ICommandBinder, we only need to focus and achieve minus write add interface does not require onTransact in Binder class to write a bunch of code if else and Parcel.read write.

    class ADILCommandBinder extends ICommandBinder {
        @Override
        public int add(int a, int b) {
            return a + b;
        }

        @Override
        public int minus(int a, int b) {
            return a - b;
        }
    }

    void main() {
        //注册binder服务
        ServiceManager.addService("command", new ADILCommandBinder());
    }

2.2 Client Process

Compared to 1.2 in the code, we find that we do not need to write Parcel.read write and BinderProxy.transact, but to construct a CommandBinderProxy object with the BinderProxy object, and then directly call CommandBinderProxy add and minus

    int add(int a, int b) {
        BinderProxy mClient = ServiceManager.getService("command");
        return new CommandBinderProxy(mClient).add(a, b);
    }

    int minus(int a, int b) {
        BinderProxy mClient = ServiceManager.getService("command");
        return new CommandBinderProxy(mClient).minus(a, b);
    }

3 ADIL what code is automatically generated

Generating three parts: ICommand, ICommandBinder, CommandBinderProxy

3.1 ICommand

Looks almost aidl file

    interface ICommand {
        int add(int a, int b);
        int minus(int a, int b);
    }

3.2 ICommandBinder

Inherited from Binder, and implement ICommand, and then calls to add and minus method has not been implemented in the method onTransact

   abstract public class ICommandBinder extends Binder implements ICommand {
        int add = 1;
        int minus = 2;

        @Override
        protected boolean onTransact(int code, @NonNull Parcel data, @Nullable Parcel reply, int flags) throws RemoteException {

            if (code == 1) {
                int a = data.readInt();
                int b = data.readInt();
                reply.writeInt(add(a, b));
                return true;
            } else if (code == 2) {
                int a = data.readInt();
                int b = data.readInt();
                reply.writeInt(minus(a, b));
                return true;
            }

            return super.onTransact(code, data, reply, flags);
        }

        abstract public int add(int a, int b);

        abstract public int minus(int a, int b);

    }

3.3 CommandBinderProxy

BinderProxy of encapsulation, add the call is converted to CommandBinderProxy Parcel.write, read and BinderProxy.transact codes.

    public class CommandBinderProxy implements ICommand {

        private BinderProxy remote;

        int add = 1;
        int minus = 2;

        public CommandBinderProxy(BinderProxy remote) {
            this.remote = remote;
        }

        @Override
        public int add(int a, int b) {
            Parcel data = Parcel.obtain();
            data.writeInt(a);
            data.writeInt(b);
            Parcel reply = Parcel.obtain();
            remote.transact(add, data, reply, 0);
            int result = reply.readInt();
            return result;
        }

        @Override
        public int minus(int a, int b) {
            int code = 2;
            Parcel data = Parcel.obtain();
            data.writeInt(a);
            data.writeInt(b);
            Parcel reply = Parcel.obtain();
            remote.transact(code, data, reply, 0);
            int result = reply.readInt();
            return result;
        }
    }

to sum up

After reading should understand the role of the main AIDL
a. Lazy, a lot less code you write, especially when hundreds of methods, AIDL come in great handy.
b. Allow the server to focus more on implementation of the interface, while reducing the possibility of mistakes
c. norms client-side and server-side interface definition, contribute iterative code