弄清楚startActivity的Binder流程
startActivity -> ActivityManager.getService().startActivity(xx) -> 8.0
startActivity -> ActivityManagerNative.getDefault().startActivity() -> 6.0
在当前进程发起startActivity的调用 (场景:启动一个新的应用的activity)
需要启动一个新的应用,那么就意味着需要,创建新的进程来承载新启动的activity,
这个过程是需要在system_server的ActivityManagerService中进行处理,那么这里就存在,需要在当前进程,
需要跨进程调用到ActivityManagerService中的startActivity方法,这个时候就使用到到Binder来实现IPC通信.
Binder的机制是一个C/S架构,
发起startActivity的这个进程就是client ,starActivity的最终执行者AMS就是server.
那么首先server端AMS中到底有那些方法可以暴露给client端,那么这个时候定义一个接口 IActivityManager来表示具体
有那些方法暴露出来了.
然后AMS必然会实现IActivityManager中的方法.
因为这个过程使用的是Binder机制,因此IActivityManager 继承于IInterface 但是并未实现asBinder方法
client端ActivityManagerProxy实现了IActivityManager接口并实现了asBinder方法
在ActivityManagerProxy被创建的时候,将server端的代理者传递给了ActivityManagerProxy
当ActivityManagerProxy在执行startActivity方法的时候会做3步处理:
1)保存调用者的相关数据和需要服务端的回复数据,如构建
Parcel data = Parcel.obtain(); Parcel reply = Parcel.obtain();
并将数据写入data中
2)使用服务端的代理者发起方法的调用
mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0);
3)处理返回结果 reply.readException();
int result = reply.readInt();
reply.recycle()
data.recycle();
mRemote.transact就走Binder的流程从java层进入到native层一步步调用到AMS的startActivity完成这次IPC通信
另一个问题mRemote是怎样生成和传递过来的呢?
从ActivityManagerNative中可以发现端倪:
public abstract class ActivityManagerNative extends Binder implements IActivityManager
{
/**
* Cast a Binder object into an activity manager interface, generating
* a proxy if needed.
*/
static public IActivityManager asInterface(IBinder obj) {
if (obj == null) {
return null;
}
IActivityManager in =
(IActivityManager)obj.queryLocalInterface(descriptor);
if (in != null) {
return in;
}
return new ActivityManagerProxy(obj);
}
/**
* Retrieve the system's default/global activity manager.
*/
//拿到client端的代理者
static public IActivityManager getDefault() {
return gDefault.get();
}
//构造函数
public ActivityManagerNative() {
attachInterface(this, descriptor);
}
public IBinder asBinder() {
return this;
}
private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() {
protected IActivityManager create() {
IBinder b = ServiceManager.getService("activity");
if (false) {
Log.v("ActivityManager", "default service binder = " + b);
}
IActivityManager am = asInterface(b);// 将从ServiceManager池里拿到的service,转换为IActivityManager
if (false) {
Log.v("ActivityManager", "default service = " + am);
}
return am;
}
};
}
我们对比8.0和6.0代码的调用差别会发现
8.0 ActivityManager.getService().startActivity(xx)
public static IActivityManager getService() {
return IActivityManagerSingleton.get();
}
private static final Singleton<IActivityManager> IActivityManagerSingleton =
new Singleton<IActivityManager>() {
@Override
protected IActivityManager create() {
final IBinder b = ServiceManager.getService(Context.ACTIVITY_SERVICE);
final IActivityManager am = IActivityManager.Stub.asInterface(b);
return am;
}
};
IActivityManager am = IActivityManager.Stub.asInterface(b);这段代码也是将拿到的service进行转化
他和6.0中使用ActivityManagerNative的asInterface转换逻辑一样的,
我们追查一下源码可以发现
public interface IActivityManager extends android.os.IInterface
{
/** Local-side IPC implementation stub class. */
public static abstract class Stub extends android.os.Binder implements android.app.IActivityManager
// 1 ) 首先IActivityManager 也是继承了android.os.IInterface
// 2) IActivityManager.Stub 是继承了android.os.Binder 并实现了android.app.IActivityManager
// 这一步的操作其实与
public abstract class ActivityManagerNative extends Binder implements IActivityManager
的这个操作一样,所以他们的原理是一样的
// 3) 他们的区别在于 8.0 中IActivityManager是定义的IActivityManager.aidl文件 ,最后由系统编译
// 生成了 IActivityManager.java文件 在这个文件里面我们看到如下
包好了两个部分操作
(1) 生成Stub类
(2) 生成client的代理者Proxy并实现了android.app.IActivityManager
6.0中的ActivityManagerNative其实就是IActivityManager.aidl文件转为之后的Stub类,
ActivityManagerProxy就是Stub的内部类Proxy
其他原理逻辑都一样,拿到服务,转换服务,返回binder
同样的在6.0中ActivityManagerService是继承了ActivityManagerNative,
在8.0中ActivityManagerService就继承了 IActivityManager.Stub
IAtivityManager.aidl 编译之后生成的文件:
public interface IActivityManager extends android.os.IInterface
{
/** Local-side IPC implementation stub class. */
public static abstract class Stub extends android.os.Binder implements android.app.IActivityManager
{
private static final java.lang.String DESCRIPTOR = "android.app.IActivityManager";
/** Construct the stub at attach it to the interface. */
public Stub()
{
this.attachInterface(this, DESCRIPTOR);
}
/**
* Cast an IBinder object into an android.app.IActivityManager interface,
* generating a proxy if needed.
*/
public static android.app.IActivityManager asInterface(android.os.IBinder obj)
{
if ((obj==null)) {
return null;
}
android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
if (((iin!=null)&&(iin instanceof android.app.IActivityManager))) {
return ((android.app.IActivityManager)iin);
}
return new android.app.IActivityManager.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_openContentUri:
{
data.enforceInterface(DESCRIPTOR);
java.lang.String _arg0;
_arg0 = data.readString();
android.os.ParcelFileDescriptor _result = this.openContentUri(_arg0);
reply.writeNoException();
if ((_result!=null)) {
reply.writeInt(1);
_result.writeToParcel(reply, android.os.Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
}
else {
reply.writeInt(0);
}
return true;
}
case TRANSACTION_handleApplicationCrash:
{
data.enforceInterface(DESCRIPTOR);
android.os.IBinder _arg0;
_arg0 = data.readStrongBinder();
android.app.ApplicationErrorReport.ParcelableCrashInfo _arg1;
if ((0!=data.readInt())) {
_arg1 = android.app.ApplicationErrorReport.ParcelableCrashInfo.CREATOR.createFromParcel(data);
}
else {
_arg1 = null;
}
this.handleApplicationCrash(_arg0, _arg1);
reply.writeNoException();
return true;
}
case TRANSACTION_startActivity:
{
data.enforceInterface(DESCRIPTOR);
android.app.IApplicationThread _arg0;
_arg0 = android.app.IApplicationThread.Stub.asInterface(data.readStrongBinder());
java.lang.String _arg1;
_arg1 = data.readString();
android.content.Intent _arg2;
if ((0!=data.readInt())) {
_arg2 = android.content.Intent.CREATOR.createFromParcel(data);
}
else {
_arg2 = null;
}
java.lang.String _arg3;
_arg3 = data.readString();
android.os.IBinder _arg4;
_arg4 = data.readStrongBinder();
java.lang.String _arg5;
_arg5 = data.readString();
int _arg6;
_arg6 = data.readInt();
int _arg7;
_arg7 = data.readInt();
android.app.ProfilerInfo _arg8;
if ((0!=data.readInt())) {
_arg8 = android.app.ProfilerInfo.CREATOR.createFromParcel(data);
}
else {
_arg8 = null;
}
android.os.Bundle _arg9;
if ((0!=data.readInt())) {
_arg9 = android.os.Bundle.CREATOR.createFromParcel(data);
}
else {
_arg9 = null;
}
int _result = this.startActivity(_arg0, _arg1, _arg2, _arg3, _arg4, _arg5, _arg6, _arg7, _arg8, _arg9);
reply.writeNoException();
reply.writeInt(_result);
return true;
}
private static class Proxy implements android.app.IActivityManager
{
private android.os.IBinder mRemote;
Proxy(android.os.IBinder remote)
{
mRemote = remote;
}
@Override public int startActivity(android.app.IApplicationThread caller, java.lang.String callingPackage, android.content.Intent intent, java.lang.String resolvedType, android.os.IBinder resultTo, java.lang.String resultWho, int requestCode, int flags, android.app.ProfilerInfo profilerInfo, android.os.Bundle options) throws android.os.RemoteException
{
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
int _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
_data.writeStrongBinder((((caller!=null))?(caller.asBinder()):(null)));
_data.writeString(callingPackage);
if ((intent!=null)) {
_data.writeInt(1);
intent.writeToParcel(_data, 0);
}
else {
_data.writeInt(0);
}
_data.writeString(resolvedType);
_data.writeStrongBinder(resultTo);
_data.writeString(resultWho);
_data.writeInt(requestCode);
_data.writeInt(flags);
if ((profilerInfo!=null)) {
_data.writeInt(1);
profilerInfo.writeToParcel(_data, 0);
}
else {
_data.writeInt(0);
}
if ((options!=null)) {
_data.writeInt(1);
options.writeToParcel(_data, 0);
}
else {
_data.writeInt(0);
}
mRemote.transact(Stub.TRANSACTION_startActivity, _data, _reply, 0);
_reply.readException();
_result = _reply.readInt();
}
finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
参考: