在匕首2中发现了一个依赖循环

Question

我尝试为DatePickerDialog提供片段，但是当我使用BasicInfoFragment作为参数时，会导致错误： Found a dependency cycle为什么会发生？

@Module
class ActivityModule(val activity: AppCompatActivity) {

    @Provides
    fun provideActivity() = activity

    @Provides
    @ActivityContext
    fun provideContext(): Context = activity

    // [...]
    @Provides
    fun provideDatePickerDialog(basicInfoFragment: BasicInfoFragment): 
    DatePickerDialog {
        return DatePickerDialog(activity, basicInfoFragment, 1999, 9, 9)
    }
}

片段代码：

class BasicInfoFragment @Inject constructor()
    : BaseFragment(), BasicInfoMvpView , 
      LabelledSpinner.OnItemChosenListener, 
      DatePickerDialog.OnDateSetListener {

    @Inject
    lateinit var datePickerDialog: DatePickerDialog

    @Inject
    lateinit var mPresenter: BasicInfoMvpPresenter<BasicInfoMvpView>

    // user info
    private lateinit var gender: DataManager.UserGender
    private var birthOfDate: Long = 0L


    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        // Inflate the layout for this fragment
        val view = inflater.inflate(R.layout.base_user_info_layout, container, false)

        activityComponent?.let {
            it.inject(this)
            mPresenter.onAttach(this)
        }

        return view
    }

    override fun onDateSet(dataPicker: DatePicker?, year: Int, month: Int, dayOfMonth: Int) {
        birthOfDate = GregorianCalendar(year, month, dayOfMonth).timeInMillis
    }
}

Answer 1

在您的provideDatePickerDialog您需要一个BasicInfoFragment ，但是当您还尝试在BasicInfoFragment注入DatePickerDialog时。 因此，鸡肉或鸡蛋的问题-要创建它们中的一个，就需要另一个。

需要考虑的其他事项：在DateTimePicker的构造函数中，您确实需要DatePickerDialog.OnDateSetListener而不是BasicInfoFragment 。

解决方案1

更改providerDatePickerDialog，如下所示

@Provides
fun provideDatePickerDialog(basicInfoFragment: BasicInfoFragment): 
DatePickerDialog {
    return DatePickerDialog(activity)
}

然后在片段中设置侦听器和日期。 在这里查看文档

解决方案2

不要为DatePickerDialog提供Dagger，而是在BasicInfoFragment中使用以下代码行创建它：

DatePickerDialog(activity, this, 1999, 9, 9)

这样，您还将消除其他可能的问题和困惑。