android 源码部分API
本文记录博主在阅读android源码过程中底层部分API！
- sp<Surface> android_view_Surface_getSurface(JNIEnv* env, jobject surfaceObj)
参数：surfaceObj – java对象Surface
返回：java对象Surface有一个long类型的mNativeObject成员，它表示java对象Surface持有Native层Surface的指针，该函数就是返回这个指针
- ANativeObjectBase类的getSelf函数
解释：getSelf有多个重载函数，函数都是将参数类型强转为返回值类型，其中一个源码如下：
static inline TYPE* getSelf(NATIVE_TYPE* self) {
return static_cast<TYPE*>(self);
}
- jobject jniCreateFileDescriptor(C_JNIEnv* env, int fd)
为这个fd文件描述符，创建一个FileDescriptor的java包裹类；也就是new FileDescriptor类，为其descriptor成员设置值fd，该方法用处通常用来保存native层打开的一些属性唯一值，如c++的socket返回值；
jobject jniCreateFileDescriptor(C_JNIEnv* env, int fd) {
JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
JniConstants::init(e);
<init>也就是java的构造方法，()V是方法签名，JniConstants::fileDescriptorClass是一个字符串
“java/io/FileDescriptor”
static jmethodID ctor = e->GetMethodID(JniConstants::fileDescriptorClass, "<init>", "()V");
jobject fileDescriptor = (*env)->NewObject(e, JniConstants::fileDescriptorClass, ctor);
// NOTE: NewObject ensures that an OutOfMemoryError will be seen by the Java
// caller if the alloc fails, so we just return NULL when that happens.
if (fileDescriptor != NULL) {
//设置成员descriptor值为fd
jniSetFileDescriptorOfFD(env, fileDescriptor, fd);
}
return fileDescriptor;
}
如何重启系统
调用电源管理模块Binder服务reboot即可
void rebootSystem(String reason) {
Slog.i(TAG, "Rebooting system because: " + reason);
IPowerManager pms = (IPowerManager)ServiceManager.getService(Context.POWER_SERVICE);
try {
pms.reboot(false, reason, false);
} catch (RemoteException ex) {
}
}
获取系统服务为什么强转没有出错
如下代码：
SearchManager seach = (SearchManager)context.getSystemService(Context.SEARCH_SERVICE);
为什么强转没事？是因为提前存储好了，存储在哪个地方呢？在SystemServiceRegistry类里面的静态代码块里面，如下格式代码：
static {
registerService(Context.SEARCH_SERVICE, SearchManager.class,
new CachedServiceFetcher<SearchManager>() {
@Override
public SearchManager createService(ContextImpl ctx) throws ServiceNotFoundException {
return new SearchManager(ctx.getOuterContext(),
ctx.mMainThread.getHandler());
}});
}
注册服务
private static <T> void registerService(String serviceName, Class<T> serviceClass,
ServiceFetcher<T> serviceFetcher) {
以下是Map格式
SYSTEM_SERVICE_NAMES.put(serviceClass, serviceName);
以下也是Map格式，value是Fetcher,用于创建具体的服务，当然这个服务知识Binder客户端，不是服务端
SYSTEM_SERVICE_FETCHERS.put(serviceName, serviceFetcher);
}
启动系统服务之反射
当我们在写系统服务时，通常会看到这样的代码：
这是一个aidl服务
public class SearchManagerService extends ISearchManager.Stub {
内部类Lifecycle继承SystemService
public static class Lifecycle extends SystemService {
private SearchManagerService mService;
public Lifecycle(Context context) {
super(context);
}
@Override
public void onStart() {
创建自己的服务
mService = new SearchManagerService(getContext());
调用SystemService方法，实质就是将服务加入到Binder服务列表中去
publishBinderService(Context.SEARCH_SERVICE, mService);
}
}
}
所以从上所知，只需要调用onStart方法就可以启动我们的服务了；那在哪个地方调用了onStart方法呢？
答案就在SystemServer中，请看下面代码：
声明了SearchManagerService的内部类Lifecycle
private static final String SEARCH_MANAGER_SERVICE_CLASS =
"com.android.server.search.SearchManagerService$Lifecycle";
mSystemServiceManager类型就是SystemServiceManager
mSystemServiceManager.startService(SEARCH_MANAGER_SERVICE_CLASS);
我们去看看SystemServiceManager里面的startService方法：
public SystemService startService(String className) {
final Class<SystemService> serviceClass;
try {
反射获取类Lifecycle
serviceClass = (Class<SystemService>)Class.forName(className);
} catch (ClassNotFoundException ex) {
Slog.i(TAG, "Starting " + className);
throw new RuntimeException("Failed to create service " + className
+ ": service class not found, usually indicates that the caller should "
+ "have called PackageManager.hasSystemFeature() to check whether the "
+ "feature is available on this device before trying to start the "
+ "services that implement it", ex);
}
return startService(serviceClass);
}
public <T extends SystemService> T startService(Class<T> serviceClass) {
try {
final String name = serviceClass.getName();
...
// Create the service.
if (!SystemService.class.isAssignableFrom(serviceClass)) {
throw new RuntimeException("Failed to create " + name
+ ": service must extend " + SystemService.class.getName());
}
final T service;
....获取类的构造方法并调用构造方法创建Lifecycle的对象
Constructor<T> constructor = serviceClass.getConstructor(Context.class);
service = constructor.newInstance(mContext);
....
再次调用重载函数
startService(service);
return service;
} finally {
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
}
}
public void startService(@NonNull final SystemService service) {
// Register it.
mServices.add(service);
// Start it.
long time = System.currentTimeMillis();
try {
调用Service的onstart方法，也就是最开始SearchManagerService的内部类Lifecycle的onStart方法
service.onStart();
} catch (RuntimeException ex) {
throw new RuntimeException("Failed to start service " + service.getClass().getName()
+ ": onStart threw an exception", ex);
}
warnIfTooLong(System.currentTimeMillis() - time, service, "onStart");
}