Android 官方推荐 : DialogFragment 创建对话框

DialogFragment有两种实现方式，我采用的是实现onCreateDialog方法，但是在使用的过程中发现onViewCreated方法并没有被回调（我在该方法中开启子线程获取需要展示的数据）。

/**
     * Called immediately after {@link #onCreateView(LayoutInflater, ViewGroup, Bundle)}
     * has returned, but before any saved state has been restored in to the view.
     * This gives subclasses a chance to initialize themselves once
     * they know their view hierarchy has been completely created.  The fragment's
     * view hierarchy is not however attached to its parent at this point.
     * @param view The View returned by {@link #onCreateView(LayoutInflater, ViewGroup, Bundle)}.
     * @param savedInstanceState If non-null, this fragment is being re-constructed
     * from a previous saved state as given here.
     */
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    }

根据方法的介绍我们知道onViewCreated应该是在onCreateView执行之后会被调用的，但是其实这里是有一个前提的，即onCreateView返回的view不为 null，这里的逻辑可以在FragmentManager中找到：

f.mView = f.performCreateView(f.performGetLayoutInflater(
                  f.mSavedFragmentState), container, f.mSavedFragmentState);
if (f.mView != null) {
     f.mInnerView = f.mView;
     f.mView.setSaveFromParentEnabled(false);
     if (container != null) {
          container.addView(f.mView);
     }
     if (f.mHidden) {
           f.mView.setVisibility(View.GONE);
     }
     f.onViewCreated(f.mView, f.mSavedFragmentState);
     dispatchOnFragmentViewCreated(f, f.mView, f.mSavedFragmentState, false);
      // Only animate the view if it is visible. This is done after
      // dispatchOnFragmentViewCreated in case visibility is changed
      f.mIsNewlyAdded = (f.mView.getVisibility() == View.VISIBLE) && f.mContainer != null;
}

performCreateView方法只会调用onCreateView，这里返回的view也即是onCreateView返回的view，可以看到只有不为null的时候才会继续执行 f.onViewCreated(f.mView, f.mSavedFragmentState); 而onCreateView方法默认是返回null：

    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
            @Nullable Bundle savedInstanceState) {
        return null;
    }

这也是为什么我的DialogFragment的onViewCreated不执行的原因。如果用重写onCreateView创建Dialog的方式就不会出现这种情况。

那有没有用onCreateDialog也能执行onViewCreated方法的办法呢？当然有！就是自己调用：

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        Timber.i("onCreateDialog");
        AlertDialog dialog = new AlertDialog.Builder(getContext())
                .setMessage("this is a dialog form onCreateDialog")
                .create();
        onViewCreated(dialog.findViewById(R.id.fl_root), savedInstanceState);
        return dialog;
    }

还有一种方法，同时复写onCreateDialog以及onCreateView，这样onCreateView返回的view不为null，接着也会触发onViewCreated方法。并且同时实现时展示的是onCreateDialog返回的dialog。