Fragment的onAttach方法

Android

很多人都建议使用fragment时从onAttach里面获取activity的引用，那么，这里获取到的activity引用是否靠谱呢？

Fragment.java

void performAttach() {
    // ...
    onAttach(mHost.getContext());
    // ...
}
/**
 * Called when a fragment is first attached to its context.
 * {@link #onCreate(Bundle)} will be called after this.
 */
@CallSuper
public void onAttach(@NonNull Context context) {
    mCalled = true;
    final Activity hostActivity = mHost == null ? null : mHost.getActivity();
    if (hostActivity != null) {
        mCalled = false;
        onAttach(hostActivity);
    }
}

mHost 即 FragmentHostCallback

public FragmentHostCallback(@NonNull Context context, @NonNull Handler handler,
        int windowAnimations) {
    this(context instanceof Activity ? (Activity) context : null, context, handler,
            windowAnimations);
}
FragmentHostCallback(@NonNull FragmentActivity activity) {
    this(activity, activity /*context*/, new Handler(), 0 /*windowAnimations*/);
}
FragmentHostCallback(@Nullable Activity activity, @NonNull Context context,
        @NonNull Handler handler, int windowAnimations) {
    mActivity = activity;
    mContext = Preconditions.checkNotNull(context, "context == null");
    mHandler = Preconditions.checkNotNull(handler, "handler == null");
    mWindowAnimations = windowAnimations;
}

其中，公共构造不会被使用到，所以一般情况下， context 均为 FragmentActivity 类型