Question

我正在使用以下ViewModel：

library(shiny)
library(shinydashboard)

# UI1 ####
ui1 <- fluidPage(
  textInput('password', label = 'Say hello')
)

# UI2 ####
header <- dashboardHeader()
sidebar <- dashboardSidebar()
body <- dashboardBody()
ui2 <- dashboardPage(header, sidebar, body)

# Server ####
server <- function(input, output){
  status <- reactiveValues(logged = F)

  observeEvent(input$password,{
    if(input$password == 'hello'){
      status$logged <- T
    }
  })

  output$uipage <- renderUI({
    if(status$logged){
      ui2
    } else {
      ui1
    }
  })
}

# UI ####
ui <- uiOutput("uipage")

shinyApp(ui = ui, server = server)

}

我在Fragment中以这种方式观察 feed ：

public class FeedViewModel extends ViewModel {

private final MutableLiveData<Photo> selectedPhoto = new MutableLiveData<>();
private final FeedRepository repository;
private LiveData<Resource<List<Photo>>> feed;

@Inject
FeedViewModel(@NonNull final FeedRepository repository) {
    this.repository = repository;
}

public void selectPhoto(@NonNull final Photo photo) {
    selectedPhoto.setValue(photo);
}

public LiveData<Photo> getSelectedPhoto() {
    return selectedPhoto;
}

LiveData<Resource<List<Photo>>> getUserFeed() {
    if (feed == null) {
        feed = new MutableLiveData<>();
        feed = repository.get();
    }
    return feed;
}

@Override
protected void onCleared() {
    super.onCleared();
}

问题是：如何以正确的方式刷新 Feed ？假设用户触发了swipeToRefresh，因此该事件必须创建一个feed的刷新任务。我如何使用ViewModel实现这一点？

Answer 1

您必须使用liveData.post（新数据）

获取数据并更新实时数据

InActivity: 
//to be called on refresh data 
vieeModel.getLatestFeed()

In View Model:
fun getLatestFeed() {
//get data from repository
feed.post(refreshedData)
}

Answer 2

您可以使用“loadTrigger”来触发数据加载，当滑动刷新时。

将此代码添加到您的片段中：

 viewModel.userFeeds.observe( 
     //add observation code
  )
 swipToRefresh.setOnRefreshListener {
        viewModel.loadFeeds()
 }

在视图模型中：

 val loadTrigger = MutableLiveData(Unit)

 val userFeeds = loadTrigger.switchMap { 
     repository.get()
 }
 fun loadFeeds() {
    loadTrigger.value = Unit
    //livedata gets fired even though the value is not changed
}

这里建议的解决方案是： manual refresh without modifying your existing LiveData

我对其进行了测试，效果很好。

如何刷新Architecture Components ViewModel中的数据

2 个答案: