Fragment getActivity详解

Fragment getActivity详解

• 首先先来看下官网对getActivity解释：
• public final Activity getActivity ()
• Return the Activity this fragment is currently associated with.
• 返回此fragment当前与之关联的Activity。

接下来我们对源码角度来分析getActivity

在日常开发中　在FragmentActivity 中调用　getSupportFragmentManager()　来进行fragment 管理，这里我们先看下　FragmentActivity源码如下：

在FragmentActivity 中调用getSupportFragmentManager() 

public class FragmentActivity extends BaseFragmentActivityJB　{

//创建　FragmentController 并　new HostCallbacks()父类就是FragmentHostCallback()
final FragmentController mFragments = FragmentController.createController(new HostCallbacks());
//创建createController　并需要传　FragmentHostCallback对象
public static final FragmentController createController(FragmentHostCallback<?> callbacks) {
    return new FragmentController(callbacks);
}
// new HostCallbacks() 并通过 super(FragmentActivity.this /*fragmentActivity*/);
//将当前FragmentActivity.this　传给FragmentHostCallback
class HostCallbacks extends FragmentHostCallback<FragmentActivity> {
   public HostCallbacks() {
      super(FragmentActivity.this /*fragmentActivity*/);
   }
}

//通过 super(FragmentActivity.this /*fragmentActivity*/)
FragmentHostCallback(FragmentActivity activity) {
    this(activity, activity /*context*/, activity.mHandler, 0 /*windowAnimations*/);
}
//mActivity 赋值
//mContext activity强转Context
//mHandler 获取activity.mHandler 
FragmentHostCallback(Activity activity, Context context, Handler handler,
        int windowAnimations) {
    mActivity = activity;
    mContext = context;
    mHandler = handler;
    mWindowAnimations = windowAnimations;
}
//mHost 是　FragmentHostCallback　调用 FragmentHostCallback.getFragmentManagerImpl()
public FragmentManager getSupportFragmentManager() {
    return mHost.getFragmentManagerImpl();
}

这里我们看到FragmentActivity　启动完成后会创建FragmentController.createController(new HostCallbacks())　并需要传HostCallbacks（）是继承FragmentHostCallback()通过 super(FragmentActivity.this /*fragmentActivity*/)　将FragmentActivity.this传给FragmentHostCallback() 并执行四个参数的构造方法　分别给mActivity 赋值，将mActivity强转　mContext并赋值mContext，获取mActivity的mHandler并赋值给mHandler，第四个参数是０

---

.我们在Fragment中调用getActivity()

//在fragment 中调用getActivity()

// Activity this fragment is attached to.
FragmentHostCallback mHost;

final public Activity getActivity() {
    return mHost == null ? null : mHost.getActivity();
}

---

最后　fragment 中调用getActivity()　这个mHost 就是我们上面说的FragmentHostCallback()是在启动FragmentActivity启动并创建FragmentController.createController(new HostCallbacks());进行赋值的，所以说getActivity()　就是获取当前正在加载fragment的Activity.