Kotlin 同一片段多项活动

Question

朋友们，我有一个问题。我可以在 activity 中使用图像中的片段。但我希望能够在不同的 activity 中查看此片段。可能吗？我使用了类似于图片中的结构，但我也在写我收到的错误。如果你能帮上忙，我会很高兴。

BreakingNewsFragment.kt

class BreakingNewsFragment : Fragment(R.layout.fragment_breaking_news) {

    lateinit var viewModel: NewsViewModel
    lateinit var viewModel2:NewsViewModel
    lateinit var newsAdapter: NewsAdapter

    val TAG = "BreakingNewsFragment"

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        viewModel = (activity as NewsActivity).viewModel
        viewModel2=(activity as UsNewsActivity).viewModel

        setupRecyclerView()

        newsAdapter.setOnItemClickListener {
            val bundle = Bundle().apply {
                putSerializable("article", it)
            }
            findNavController().navigate(
                R.id.action_breakingNewsFragment_to_articleFragment,
                bundle
            )
        }

        viewModel.breakingNews.observe(viewLifecycleOwner, Observer { response ->
            when(response) {
                is Resource.Success -> {
                    hideProgressBar()
                    response.data?.let { newsResponse ->
                        newsAdapter.differ.submitList(newsResponse.articles.toList())
                        val totalPages=newsResponse.totalResults/ QUERY_PAGE_SIZE+2 //Sayfada boşluk oluşuyor
                        isLastPage=viewModel.breakingNewsPage==totalPages
                        if(isLastPage){
                            rvBreakingNews.setPadding(0,0,0,0)
                        }
                    }
                }
                is Resource.Error -> {
                    hideProgressBar()
                    response.message?.let { message ->
                        Log.e(TAG, "An error occured: $message")
                    }
                }
                is Resource.Loading -> {
                    showProgressBar()
                }
            }
        })

    }

Error

原因：java.lang.ClassCastException：com.androiddevs.mvvmnewsapp.ui.NewsActivity 无法转换为 com.androiddevs.mvvmnewsapp.ui.UsNewsActivity 在 com.androiddevs.mvvmnewsapp.ui.fragments.BreakingNewsFragment.onViewCreated(BreakingNewsFragment.kt:34)

Answer 1

我想你在从 NewsActivity 创建片段时得到了这个？您正试图将 UsNewsActivity 视为 NewsActivity，但事实并非如此。

去吧：

val viewModel: NewsViewModel by activityViewModels()

按照建议 here。它应该给你在 Activity.

中使用的 ViewModel

如果您想坚持现在的做事方式，您可以在您的活动中实施 interface，例如

interface NewsActivityInterface {
    val viewModel: NewsViewModel
}
class MainActivity : AppCompatActivity(), NewsActivityInterface {
    override val viewModel: NewsViewModel by viewModels()
    (...)
}

然后让你的视图模型像

viewModel = (activity as NewsActivityInterface).viewModel

或检查类型：

val viewModel = activity.let{
    when (it){
        is MainActivity -> it.viewModel
        is AnotherActivity -> it.viewModel
        else -> error ("Needs correct activity")
    }
}

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