加载 View 时，我的 ViewModel 具有空值，如何延迟加载 View 直到 ViewModel 填充数据？

Question

这是我的片段 xml：

<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools">

<data>
    <variable
        name="viewModel"
        type="UserProfileViewModel" />
</data>

<ImageView
     android:id="@+id/image_user_avatar"
     app:userAvatarUrl="@{viewModel.currentUser.avatarUrl}" />

它有一个 viewModel 变量，它是下面的 Java 类：

public class UserProfileViewModel extends BaseViewModel {

private User mCurrentUser;

public void setSignedInUser(User signedInUser) {
    mCurrentUser = signedInUser;
}

public User getCurrentUser() { return mCurrentUser; }

在我的片段中：

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mUserId = getArguments().getString(Strings.KEY_USER_ID);
    }
    mViewModel = UserProfileViewModel.getInstance();
}

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    mBinding = DataBindingUtil.inflate(inflater, R.layout.fragment_user_profile, container, false);
    mBinding.setViewModel(mViewModel);
    mBinding.buttonSignOut.setOnClickListener((View view) -> signOutUser());
    mBinding.fragmentUserProfileSwipeRefreshContainer.setOnRefreshListener(this);
    return mBinding.getRoot();
}

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    getUserProfile();
}

public void getUserProfile() {
    GetUserProfileRequest request = new GetUserProfileRequest(mUserId);
    mGetUserProfileDisposable = mViewModel
            .getUserProfile(request)
            .doOnSubscribe(__ -> mBinding.fragmentUserProfileSwipeRefreshContainer.setRefreshing(true))
            .doOnError((Throwable ex) -> mBinding.fragmentUserProfileSwipeRefreshContainer.setRefreshing(false))
            .subscribe((Response<GetUserProfileResponseBody> response) -> {
                if (response.body() != null) {
// this user object has the avatarUrl field needed in the xml                       
                    mViewModel.setSignedInUser(response.body().getSignedInUser());
                }
            }, (Throwable ex) -> {
            });
}

到调用 setSignedInUser 时，Fragment 已经加载完毕，并且 XML 中的 viewModel 变量还没有被填充，所以 avatarUrl 为空，所以没有加载图像。如何防止这种情况发生？

Answer 1

试试这个

if (viewModel!= null) {

} else {
            try {
                Thread.sleep(1000);
            } catch (Exception e) {

            }
        }