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为什么会想写这篇文章，只因为一个error idl.exe E 4928 5836 type_namespace.cpp:130] 'Book' can be an out type, so you must declare it as in, out or inout. 看过上一篇文章Android：IPC之AIDL的学习和总结的同学都知道这是因为在AIDL文件中使用非常规类型作为参数传递的时候没有标记指向tag，那么到底为什么会是这样子的呢，作为一个好奇宝宝我想好好看看。
介绍
官网介绍AIDL的时候上有这么一段话
- All non-primitive parameters require a directional tag indicating which way the data goes. Either in, out, or inout (see the example below).
- Primitives are in by default, and cannot be otherwise.
- Caution: You should limit the direction to what is truly needed, because marshalling parameters is expensive.
大概意思是非默认类型的参数都需要添加指向标签in，out或inout。根据自己的需求去添加，因为实现是有代价的。
已知结论
看过我写的Android：IPC之AIDL的学习和总结的同学都知道：
- in表示输入型参数（Server可以获取到Client传递过去的数据，但是不能对Client端的数据进行修改）
- out表示输出型参数（Server获取不到Client传递过去的数据，但是能对Client端的数据进行修改）
- inout表示输入输出型参数（Server可以获取到Client传递过去的数据，但是能对Client端的数据进行修改）。
提出问题
下边我们就研究一个in，out或inout为什么能代表不同的传输方式，为什么实现的代价不一样。
过程验证
创建Book.aidl文件
package com.tzx.aidldemo.aidl;
parcelable Book;
创建Book.java文件
package com.tzx.aidldemo.aidl;
public class Book implements Parcelable {
public int bookId;
public String bookName;
public Book() {
}
public Book(int bookId, String bookName) {
this.bookId = bookId;
this.bookName = bookName;
}
//从序列化后的对象中创建原始对象
protected Book(Parcel in) {
bookId = in.readInt();
bookName = in.readString();
}
public static final Creator<Book> CREATOR = new Creator<Book>() {
//从序列化后的对象中创建原始对象
@Override
public Book createFromParcel(Parcel in) {
return new Book(in);
}
//指定长度的原始对象数组
@Override
public Book[] newArray(int size) {
return new Book[size];
}
};
//返回当前对象的内容描述。如果含有文件描述符，返回1，否则返回0，几乎所有情况都返回0
@Override
public int describeContents() {
return 0;
}
//将当前对象写入序列化结构中，其flags标识有两种（1|0）。
//为1时标识当前对象需要作为返回值返回，不能立即释放资源，几乎所有情况下都为0.
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeInt(bookId);
dest.writeString(bookName);
}
@Override
public String toString() {
return "[bookId=" + bookId + ",bookName='" + bookName + "']";
}
}
创建aidl接口文件IBookManager.aidl文件
package com.tzx.aidlinout.aidl;
import com.tzx.aidlinout.aidl.Book;
interface IBookManager {
Book addInBook(in Book book);
Book addOutBook(out Book book);
Book addInoutBook(inout Book book);
}
创建远程服务
//将bookId都改为-1，在bookName后面都添加参数的tag标记
public class BookManagerService extends Service {
private CopyOnWriteArrayList list = new CopyOnWriteArrayList();
private IBinder mBinder = new IBookManager.Stub(){
@Override
public Book addInBook(Book book) throws RemoteException {
book.bookId = -1;
book.bookName = book.bookName + "-in";
list.add(book);
return book;
}
@Override
public Book addOutBook(Book book) throws RemoteException {
book.bookId = -1;
book.bookName = book.bookName + "-out";
list.add(book);
return book;
}
@Override
public Book addInoutBook(Book book) throws RemoteException {
book.bookId = -1;
book.bookName = book.bookName + "-inout";
list.add(book);
return book;
}
@Override
public List<Book> getBookList() throws RemoteException {
return list;
}
};
@Nullable
@Override
public IBinder onBind(Intent intent) {
return mBinder;
}
}
在创建上面的文件的过程中，遇到不太清楚的或者编译出现Error的，可以参考上一篇文章Android：IPC之AIDL的学习和总结。
具体方法调用的Activity就不写全部代码了，我们看看三种方法的调用
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.book_in:
try {
int bookId = Integer.parseInt(bookIdET.getText().toString());
String bookName = bookNameET.getText().toString();
if (bookId <= 0 || TextUtils.isEmpty(bookName)) return;
StringBuilder builder = new StringBuilder();
//LogUtils.d("-----------book_in-----------------");
Book book0 = new Book(bookId, bookName);
String source = "source:" + book0.toString();
//LogUtils.d(source);
builder.append(source);
builder.append('\n');
String result = "result:" + bookManager.addInBook(book0).toString();
//LogUtils.d(result);
builder.append(result);
builder.append('\n');
source = "source" + book0.toString();
//LogUtils.d(source);
builder.append(source);
//LogUtils.d("**************book_in****************");
bookinfoTV.setText(builder.toString());
} catch (Exception e) {
e.printStackTrace();
}
break;
case R.id.book_out:
try {
int bookId = Integer.parseInt(bookIdET.getText().toString());
String bookName = bookNameET.getText().toString();
if (bookId <= 0 || TextUtils.isEmpty(bookName)) return;
StringBuilder builder = new StringBuilder();
//LogUtils.d("-----------book_out-----------------");
Book book0 = new Book(bookId, bookName);
String source = "source:" + book0.toString();
//LogUtils.d(source);
builder.append(source);
builder.append('\n');
String result = "result:" + bookManager.addOutBook(book0).toString();
//LogUtils.d(result);
builder.append(result);
builder.append('\n');
source = "source" + book0.toString();
//LogUtils.d(source);
builder.append(source);
//LogUtils.d("**************book_out****************");
bookinfoTV.setText(builder.toString());
} catch (Exception e) {
e.printStackTrace();
}
break;
case R.id.book_inout:
try {
int bookId = Integer.parseInt(bookIdET.getText().toString());
String bookName = bookNameET.getText().toString();
if (bookId <= 0 || TextUtils.isEmpty(bookName)) return;
StringBuilder builder = new StringBuilder();
//LogUtils.d("-----------book_inout-----------------");
Book book0 = new Book(bookId, bookName);
String source = "source:" + book0.toString();
//LogUtils.d(source);
builder.append(source);
builder.append('\n');
String result = "result:" + bookManager.addInoutBook(book0).toString();
//LogUtils.d(result);
builder.append(result);
builder.append('\n');
source = "source" + book0.toString();
//LogUtils.d(source);
builder.append(source);
//LogUtils.d("**************book_inout****************");
bookinfoTV.setText(builder.toString());
} catch (Exception e) {
e.printStackTrace();
}
break;
}
}
创建好上面三个文件后，我们编译整个项目工程（PS：生成aidl接口实现类）。
运行结果
[图片上传失败...(image-ed056-1524796700960)]
下边是与结果相对应的Log输出
14962-14962/com.tzx.aidlinout D/xxx: -----------book_in-----------------
14962-14962/com.tzx.aidlinout D/xxx: source:[bookId=1212,bookName=C++]
14962-14962/com.tzx.aidlinout D/xxx: result:[bookId=-1,bookName=C++-in]
14962-14962/com.tzx.aidlinout D/xxx: source[bookId=1212,bookName=C++]
14962-14962/com.tzx.aidlinout D/xxx: **************book_in****************
14962-14962/com.tzx.aidlinout D/xxx: -----------book_out-----------------
14962-14962/com.tzx.aidlinout D/xxx: source:[bookId=1212,bookName=C++]
14962-14962/com.tzx.aidlinout D/xxx: result:[bookId=-1,bookName=null-out]
14962-14962/com.tzx.aidlinout D/xxx: source[bookId=-1,bookName=null-out]
14962-14962/com.tzx.aidlinout D/xxx: **************book_out****************
14962-14962/com.tzx.aidlinout D/xxx: -----------book_inout-----------------
14962-14962/com.tzx.aidlinout D/xxx: source:[bookId=1212,bookName=C++]
14962-14962/com.tzx.aidlinout D/xxx: result:[bookId=-1,bookName=C++-inout]
14962-14962/com.tzx.aidlinout D/xxx: source[bookId=-1,bookName=C++-inout]
14962-14962/com.tzx.aidlinout D/xxx: **************book_inout****************
实际结果与我们已知结论一致！！
但问题我们还没有解决，我们继续看代码，其实所有的实现都是在改接口实现类中IBookManager.java
源码解析
package com.tzx.aidlinout.aidl;
public interface IBookManager extends android.os.IInterface {
public com.tzx.aidlinout.aidl.Book addInBook(
com.tzx.aidlinout.aidl.Book book) throws android.os.RemoteException;
public com.tzx.aidlinout.aidl.Book addOutBook(
com.tzx.aidlinout.aidl.Book book) throws android.os.RemoteException;
public com.tzx.aidlinout.aidl.Book addInoutBook(
com.tzx.aidlinout.aidl.Book book) throws android.os.RemoteException;
public java.util.List<com.tzx.aidlinout.aidl.Book> getBookList()
throws android.os.RemoteException;
/** Local-side IPC implementation stub class. */
public static abstract class Stub extends android.os.Binder implements com.tzx.aidlinout.aidl.IBookManager {
private static final java.lang.String DESCRIPTOR = "com.tzx.aidlinout.aidl.IBookManager";
static final int TRANSACTION_addInBook = (android.os.IBinder.FIRST_CALL_TRANSACTION +
0);
static final int TRANSACTION_addOutBook = (android.os.IBinder.FIRST_CALL_TRANSACTION +
1);
static final int TRANSACTION_addInoutBook = (android.os.IBinder.FIRST_CALL_TRANSACTION +
2);
static final int TRANSACTION_getBookList = (android.os.IBinder.FIRST_CALL_TRANSACTION +
3);
/** Construct the stub at attach it to the interface. */
public Stub() {
this.attachInterface(this, DESCRIPTOR);
}
/**
* Cast an IBinder object into an com.tzx.aidlinout.aidl.IBookManager interface,
* generating a proxy if needed.
*/
public static com.tzx.aidlinout.aidl.IBookManager asInterface(
android.os.IBinder obj) {
if ((obj == null)) {
return null;
}
android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
if (((iin != null) &&
(iin instanceof com.tzx.aidlinout.aidl.IBookManager))) {
return ((com.tzx.aidlinout.aidl.IBookManager) iin);
}
return new com.tzx.aidlinout.aidl.IBookManager.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_addInBook: {
data.enforceInterface(DESCRIPTOR);
//声明输入的参数_arg0的引用
com.tzx.aidlinout.aidl.Book _arg0;
//并根据输入的数据为其创建对象
if ((0 != data.readInt())) {
_arg0 = com.tzx.aidlinout.aidl.Book.CREATOR.createFromParcel(data);
} else {
_arg0 = null;
}
//获取调用this.addInBook方法返回的_result
com.tzx.aidlinout.aidl.Book _result = this.addInBook(_arg0);
reply.writeNoException();
//并向reply中写入返回值_result
if ((_result != null)) {
reply.writeInt(1);
_result.writeToParcel(reply,
android.os.Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
} else {
reply.writeInt(0);
}
return true;
}
case TRANSACTION_addOutBook: {
data.enforceInterface(DESCRIPTOR);
//声明输入的参数_arg0的引用
com.tzx.aidlinout.aidl.Book _arg0;
//并为其创建新的对象
_arg0 = new com.tzx.aidlinout.aidl.Book();
//获取调用this.addOutBook方法返回的_result
com.tzx.aidlinout.aidl.Book _result = this.addOutBook(_arg0);
reply.writeNoException();
//并向reply中写入返回值_result
if ((_result != null)) {
reply.writeInt(1);
_result.writeToParcel(reply,
android.os.Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
} else {
reply.writeInt(0);
}
//再将参数_arg0写入reply中，至于为什么写入，我们看看客户端Proxy中的读取
if ((_arg0 != null)) {
reply.writeInt(1);
_arg0.writeToParcel(reply,
android.os.Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
} else {
reply.writeInt(0);
}
return true;
}
case TRANSACTION_addInoutBook: {
data.enforceInterface(DESCRIPTOR);
//声明输入的参数_arg0的引用
com.tzx.aidlinout.aidl.Book _arg0;
//并根据输入的数据为其创建对象
if ((0 != data.readInt())) {
_arg0 = com.tzx.aidlinout.aidl.Book.CREATOR.createFromParcel(data);
} else {
_arg0 = null;
}
//获取调用this.addInoutBook方法返回的_result
com.tzx.aidlinout.aidl.Book _result = this.addInoutBook(_arg0);
reply.writeNoException();
//并向reply中写入返回值_result
if ((_result != null)) {
reply.writeInt(1);
_result.writeToParcel(reply,
android.os.Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
} else {
reply.writeInt(0);
}
//再将参数_arg0写入reply中，至于为什么写入，我们看看客户端Proxy中的读取
if ((_arg0 != null)) {
reply.writeInt(1);
_arg0.writeToParcel(reply,
android.os.Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
} else {
reply.writeInt(0);
}
return true;
}
case TRANSACTION_getBookList: {
data.enforceInterface(DESCRIPTOR);
java.util.List<com.tzx.aidlinout.aidl.Book> _result = this.getBookList();
reply.writeNoException();
reply.writeTypedList(_result);
return true;
}
}
return super.onTransact(code, data, reply, flags);
}
private static class Proxy implements com.tzx.aidlinout.aidl.IBookManager {
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 com.tzx.aidlinout.aidl.Book addInBook(
com.tzx.aidlinout.aidl.Book book)
throws android.os.RemoteException {
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
com.tzx.aidlinout.aidl.Book _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
//将客户端调用时传入的参数写入_data中
if ((book != null)) {
_data.writeInt(1);
book.writeToParcel(_data, 0);
} else {
_data.writeInt(0);
}
//将_data、_reply序列化对象和Stub.TRANSACTION_addInBook指令传递到Server端
mRemote.transact(Stub.TRANSACTION_addInBook, _data, _reply,
0);
_reply.readException();
//读取Server端返回的序列化_reply中的对象
if ((0 != _reply.readInt())) {
_result = com.tzx.aidlinout.aidl.Book.CREATOR.createFromParcel(_reply);
} else {
_result = null;
}
//然后直接将_result返回
//我们发现整个方法调用期间传入的对象book只是将数据写入到Server，它的值进行并没有任何修改。
//总结：in类型的参数，它向服务端传入数据，但是却不接受Server返回的值。
} finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
@Override
public com.tzx.aidlinout.aidl.Book addOutBook(
com.tzx.aidlinout.aidl.Book book)
throws android.os.RemoteException {
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
com.tzx.aidlinout.aidl.Book _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
//将_data、_reply序列化对象和Stub.TRANSACTION_addInBook指令传递到Server端
//_data和_reply序列化对象并没有进行写入
mRemote.transact(Stub.TRANSACTION_addOutBook, _data,
_reply, 0);
_reply.readException();
//读取Server端返回的序列化_reply中的对象，写入到_result
if ((0 != _reply.readInt())) {
_result = com.tzx.aidlinout.aidl.Book.CREATOR.createFromParcel(_reply);
} else {
_result = null;
}
//读取Server端返回的序列化_reply中的对象，写入到传入的book对象中
if ((0 != _reply.readInt())) {
book.readFromParcel(_reply);
}
//然后直接将_result返回
//我们发现整个方法调用期间传入的对象book并没有将数据写入到Server，它的值确实是Server返回的。
//总结：out类型的参数，它并不向服务端传入数据，但是却接受Server返回的值。
} finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
@Override
public com.tzx.aidlinout.aidl.Book addInoutBook(
com.tzx.aidlinout.aidl.Book book)
throws android.os.RemoteException {
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
com.tzx.aidlinout.aidl.Book _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
//将客户端调用时传入的参数写入_data中
if ((book != null)) {
_data.writeInt(1);
book.writeToParcel(_data, 0);
} else {
_data.writeInt(0);
}
//将_data、_reply序列化对象和Stub.TRANSACTION_addInoutBook指令传递到Server端
mRemote.transact(Stub.TRANSACTION_addInoutBook, _data,
_reply, 0);
_reply.readException();
//读取Server端返回的序列化_reply中的对象，写入到_result
if ((0 != _reply.readInt())) {
_result = com.tzx.aidlinout.aidl.Book.CREATOR.createFromParcel(_reply);
} else {
_result = null;
}
//读取Server端返回的序列化_reply中的对象，写入到传入的book对象中
if ((0 != _reply.readInt())) {
book.readFromParcel(_reply);
}
//然后直接将_result返回
//我们发现整个方法调用期间传入的对象book将其数据写入到Server，并且它的值被Server返回的数据修改。
//总结：inout类型的参数，它既向服务端传入数据，也却接受Server返回的值。
} finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
@Override
public java.util.List<com.tzx.aidlinout.aidl.Book> getBookList()
throws android.os.RemoteException {
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
java.util.List<com.tzx.aidlinout.aidl.Book> _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
mRemote.transact(Stub.TRANSACTION_getBookList, _data,
_reply, 0);
_reply.readException();
_result = _reply.createTypedArrayList(com.tzx.aidlinout.aidl.Book.CREATOR);
} finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
}
}
}
看了这么多代码是不是感觉脑袋大了，没事接下来一张图帮你理的清清楚楚的：
aidl-tag-type
经过两篇文章对aidl的讲解，我想你已经把它理解的透透的了，如果还有什么问题可以给我留言哦~！
想阅读作者的更多文章，可以查看我 个人博客 和公共号：
振兴书城
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