Question

我正在构建一个想要在MainActivity中显示bottomSheetFragment的应用程序。由于我正在该片段中显示一些数据（用户帐户详细信息等），因此我决定实现这一目标的最佳方法是使用modelView。

因此，我在主活动中设置数据，如下所示：

@Override
protected void onStart() {
    // Initialize view model for bottom menu.
    bottomMenuData = ViewModelProviders.of(this).get(BottomMenuData.class);
    bottomMenuData.setGoogleSignInAccount(CurrentGmailAccount);
    ...
}

现在，我观察到我的bottomSheetFragment中的值发生了变化，如下所示：

// Observe google account.
bottomMenuData.getGoogleSignInAccount().observe(getViewLifecycleOwner(), googleSignInAccount -> {
    // Load image.
    Glide.with(account_image)
         .load(googleSignInAccount.getPhotoUrl())
         .apply(new RequestOptions()
         .placeholder(R.drawable.sample_image_profile))
         .into(account_image);

         // Set other account details.
         account_name.setText(googleSignInAccount.getDisplayName());
         account_email.setText(googleSignInAccount.getEmail());
});

我尝试像这样初始化viewModel：

@Override
public void onAttach(@NonNull Context context) {
    bottomMenuData = ViewModelProviders.of(getActivity()).get(BottomMenuData.class);
    super.onAttach(context);
}

问题是我在这里遇到异常，说我尝试在onCreateView（）之前进行活动。片段的生命周期表示onAttach在onCreateView（）之后运行。我也尝试初始化viewModel onViewCreated（），但是代码从未在那里执行！我已经阅读了几乎整个互联网，但是无法正常工作！

感谢您的帮助！

编辑：这是我的viewModel的源代码：

public class DataModel extends ViewModel {
    /** The current gmail account. */
    private MutableLiveData<GoogleSignInAccount> currentGmailAccount = new MutableLiveData<>();
    /** List containing messages history. */
    private MutableLiveData<List<MsgModel>> messagesList = new MutableLiveData<>();
    /** Listener to invoke callbacks for item clicks. */
    private MutableLiveData<SettingsListener> settingsListener = new MutableLiveData<>();
    /** Defines if it is the first run (first onCreate). */
    boolean firstRun = true;

    /**
     * Add a new message to messages list.
     * @param message Message to add.
     */
    void AddMessage(MsgModel message) {
        // Make sure list is initialized.
        if (messagesList.getValue() == null) messagesList.setValue(new ArrayList<>());

        // Add new message.
        messagesList.getValue().add(message);
    }

    /**
     * Defines how many messages are in the messages list.
     * @return The count of the messages in the messages list.
     */
    int MessagesSize() {
        // Make sure list is initialized.
        if (messagesList.getValue() == null) messagesList.setValue(new ArrayList<>());

        return  messagesList.getValue().size();
    }

    /**
     * Get current gmail account as set from {@Link MainActivity}.
     * @return Current gmail account. May be null if requested before set.
     */
    GoogleSignInAccount GetCurrentGmailAccount() {
        return currentGmailAccount.getValue();
    }

    @NonNull
    public MutableLiveData<GoogleSignInAccount> GetGoogleSignInAccount() {
        return currentGmailAccount;
    }

    void SetGoogleSignInAccount(GoogleSignInAccount googleSignInAccount) {
        this.currentGmailAccount.setValue(googleSignInAccount);
    }

    @NonNull
    public SettingsListener GetSettingsListener() {
        return settingsListener.getValue();
    }

    void SetSettingsListener(SettingsListener settingsListener) {
        this.settingsListener.setValue(settingsListener);
    }

    @NonNull
    MutableLiveData<List<MsgModel>> GetMessagesList() {
        // Make sure list is initialized.
        if (messagesList.getValue() == null) messagesList.setValue(new ArrayList<>());

        return messagesList;
    }
}

Answer 1

getActivity（）在您的片段正在准备中并且即将准备就绪时可以为null。将您的ViewModel参考/实例创建移动到[onActivityCreated] [1]

[1]：https://developer.android.com/reference/android/app/Fragment.html#onActivityCreated(android.os.Bundle)，如下所示，

void onActivityCreated (Bundle savedInstanceState) {
    bottomMenuData = 
ViewModelProviders.of(getActivity()).get(BottomMenuData.class);

}

BottomSheetFragment中的ModelView

1 个答案: