android,NativeActivity使用

blog地址：http://www.flakor.cn/2014-12-09-568.html

android现在已经支持C/C++ NativeActivity开发

android提供[code lang="c"][/code]头文件。所以你要使用的话，要引入这个头文件

1，NativeActivity 入口

入口函数必须是
[code lang="c"]void ANativeActivity_onCreate(ANativeActivity* activity,
void* savedState, size_t savedStateSize)[/code]

因为头文件就是这么定义的。而且必须有。不然不能使用native activity。它的定义如下：

[code lang="c"]/**
* This is the function that must be in the native code to instantiate the
* application's native activity. It is called with the activity instance (see
* above); if the code is being instantiated from a previously saved instance,
* the savedState will be non-NULL and point to the saved data. You must make
* any copy of this data you need -- it will be released after you return from
* this function.
*/
typedef void ANativeActivity_createFunc(ANativeActivity* activity,
void* savedState, size_t savedStateSize);

/**
* The name of the function that NativeInstance looks for when launching its
* native code. This is the default function that is used, you can specify
* "android.app.func_name" string meta-data in your manifest to use a different
* function.
*/
extern ANativeActivity_createFunc ANativeActivity_onCreate;[/code]

2,定义native activity的生命周期回调接口函数。

这些接口的名字和java端的是类似的。它的定义如下：

[code lang="c"]/**
* These are the callbacks the framework makes into a native application.
* All of these callbacks happen on the main thread of the application.
* By default, all callbacks are NULL; set to a pointer to your own function
* to have it called.
*/
typedef struct ANativeActivityCallbacks {
/**
* NativeActivity has started. See Java documentation for Activity.onStart()
* for more information.
*/
void (*onStart)(ANativeActivity* activity);

/**
* NativeActivity has resumed. See Java documentation for Activity.onResume()
* for more information.
*/
void (*onResume)(ANativeActivity* activity);

/**
* Framework is asking NativeActivity to save its current instance state.
* See Java documentation for Activity.onSaveInstanceState() for more
* information. The returned pointer needs to be created with malloc();
* the framework will call free() on it for you. You also must fill in
* outSize with the number of bytes in the allocation. Note that the
* saved state will be persisted, so it can not contain any active
* entities (pointers to memory, file descriptors, etc).
*/
void* (*onSaveInstanceState)(ANativeActivity* activity, size_t* outSize);

/**
* NativeActivity has paused. See Java documentation for Activity.onPause()
* for more information.
*/
void (*onPause)(ANativeActivity* activity);

/**
* NativeActivity has stopped. See Java documentation for Activity.onStop()
* for more information.
*/
void (*onStop)(ANativeActivity* activity);

/**
* NativeActivity is being destroyed. See Java documentation for Activity.onDestroy()
* for more information.
*/
void (*onDestroy)(ANativeActivity* activity);

/**
* Focus has changed in this NativeActivity's window. This is often used,
* for example, to pause a game when it loses input focus.
*/
void (*onWindowFocusChanged)(ANativeActivity* activity, int hasFocus);

/**
* The drawing window for this native activity has been created. You
* can use the given native window object to start drawing.
*/
void (*onNativeWindowCreated)(ANativeActivity* activity, ANativeWindow* window);

/**
* The drawing window for this native activity has been resized. You should
* retrieve the new size from the window and ensure that your rendering in
* it now matches.
*/
void (*onNativeWindowResized)(ANativeActivity* activity, ANativeWindow* window);

/**
* The drawing window for this native activity needs to be redrawn. To avoid
* transient artifacts during screen changes (such resizing after rotation),
* applications should not return from this function until they have finished
* drawing their window in its current state.
*/
void (*onNativeWindowRedrawNeeded)(ANativeActivity* activity, ANativeWindow* window);

/**
* The drawing window for this native activity is going to be destroyed.
* You MUST ensure that you do not touch the window object after returning
* from this function: in the common case of drawing to the window from
* another thread, that means the implementation of this callback must
* properly synchronize with the other thread to stop its drawing before
* returning from here.
*/
void (*onNativeWindowDestroyed)(ANativeActivity* activity, ANativeWindow* window);

/**
* The input queue for this native activity's window has been created.
* You can use the given input queue to start retrieving input events.
*/
void (*onInputQueueCreated)(ANativeActivity* activity, AInputQueue* queue);

/**
* The input queue for this native activity's window is being destroyed.
* You should no longer try to reference this object upon returning from this
* function.
*/
void (*onInputQueueDestroyed)(ANativeActivity* activity, AInputQueue* queue);

/**
* The rectangle in the window in which content should be placed has changed.
*/
void (*onContentRectChanged)(ANativeActivity* activity, const ARect* rect);

/**
* The current device AConfiguration has changed. The new configuration can
* be retrieved from assetManager.
*/
void (*onConfigurationChanged)(ANativeActivity* activity);

/**
* The system is running low on memory. Use this callback to release
* resources you do not need, to help the system avoid killing more
* important processes.
*/
void (*onLowMemory)(ANativeActivity* activity);
} ANativeActivityCallbacks;[/code]

这里它定义了16个函数指针，你需要在ANativeActivity_onCreate函数里面将这些自己定义的回调函数赋给ANativeActivity的callback的相应函数指针。例如：
[code lang="c"]void ANativeActivity_onCreate(ANativeActivity* activity,
void* savedState, size_t savedStateSize) {
LOGV("Creating: %p\n", activity);
activity->callbacks->onDestroy = onDestroy;
activity->callbacks->onStart = onStart;
activity->callbacks->onResume = onResume;
activity->callbacks->onSaveInstanceState = onSaveInstanceState;
activity->callbacks->onPause = onPause;
activity->callbacks->onStop = onStop;
activity->callbacks->onConfigurationChanged = onConfigurationChanged;
activity->callbacks->onLowMemory = onLowMemory;
activity->callbacks->onWindowFocusChanged = onWindowFocusChanged;
activity->callbacks->onNativeWindowCreated = onNativeWindowCreated;
activity->callbacks->onNativeWindowDestroyed = onNativeWindowDestroyed;
activity->callbacks->onInputQueueCreated = onInputQueueCreated;
activity->callbacks->onInputQueueDestroyed = onInputQueueDestroyed;
//其他代码...
}[/code]

上面的onDestroy这些都是你自己定义的接口函数。函数类型要和它提供的接口函数指针一样。

3.manifest文件的配置

manifest里面其他是一样的，只有actvity和一般的不一样

[code lang="xml"]

android:label="@string/app_name"
android:configChanges="orientation|keyboardHidden">

android:value="NativeActivity" />

[/code]
这里有两种情况。
1.完全不用java
上面这个例子就是完全不用java的。这时候你的activity的android:name属性就必须等于android.app.NativeActivity。另外在application里添加属性android:hasCode="false"，表示没有java代码
2，有一个NativeActivity子类
你是java里继承NativeActivity，这时activity的android:name属性就等于你自己的activity名字。这个activity必须是NativeActivity的子类，不然没法用NDK的东西。application里添加属性android:hasCode="ture"。

以上只是简单介绍了NativeActivity，你要完全使用它，还需学习ALooper，pipe和pthread等知识。有时间再做介绍.

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