转：http://blog.csdn.net/xiruanliuwei/article/details/7560914
Android NDK为我们提供了两种方式来实现我们的native activity：
1、The native_activity.h header defines the native version of the NativeActivity class. It
contains the callback interface and data structures that you need to create your native
activity. Because the main thread of your application handles the callbacks, your callback
implementations must not be blocking. If they block, you might receive ANR (Application Not
Responding) errors because your main thread will be unresponsive until the callback returns.
Read the comments in the
<ndk_root>/platforms/android-9/arch-arm/usr/include/android/native_activity.h file for
more information.
2、The android_native_app_glue.h file defines a static helper library built on top of the
native_activity.h interface. It spawns another thread to handle things such as callbacks or
input events. This prevents any callbacks from blocking your main thread and adds some
flexibility in how you implement the callbacks, so you might find this programming model a
bit easier to implement.
The <ndk_root>/sources/android/native_app_glue/android_native_app_glue.c
source is also available to you, so you can modify the implementation if you need. Read the
comments in the <ndk_root>/sources/android/native_app_glue/android_native_app_glue.h
file for more information.
通过上面的描述，我们可以发现方式二会简单一些。在使用方式一实现native activity时，
需要注意在实现回调函数时，不要阻塞了main UI thread，否则会出现ANR。而方式二中，
则在一个新线程中创建一个事件循环执行回调函数，因此不会造成main UI thread阻塞。