秒表时间跨度的列表视图 - 如何在 UI 中继续计时器

Question

我有一个活动列表视图，每个活动都包含从我的 MongoDB 集合中提取的时间跨度。在点击一个活动列表视图项目时，我启动我的秒表，将当前时间跨度添加到经过的时间，这工作正常。但是唯一的问题是，计时器不会继续在 UI 中运行，时间跨度只会在每次点击时更新到 UI。

您能否建议我应该如何根据每个点击的活动继续运行各个计时器？请参阅下面的列表视图和 Tapped Event 方法：

列表视图

 <ListView
                     x:Name="ActivitiesList"
                     SelectionMode="None"
                     CachingStrategy="RetainElement"
                     HasUnevenRows="True"                     
                     BackgroundColor="White"                    
                     IsPullToRefreshEnabled="True"
                     ItemsSource="{Binding UserActivitiesList }"
                     RefreshCommand="{Binding getUserActivities}"
                     IsRefreshing="{Binding IsBusy, Mode=OneWay}"                    
                     SeparatorVisibility="None"
                     RowHeight="70"                      
                    >
                    <ListView.ItemTemplate>
                        <DataTemplate >
                            <ViewCell
                                Height="60" Tapped="OnActivityTap"
                             > 
                                
                                <StackLayout>
                                    <Grid BackgroundColor="White" x:Name="activitiesGrid"
                                          HeightRequest="60" WidthRequest="600" Margin="20,0,20,0" >

                                        <Grid.RowDefinitions>                                                                                
                                            <RowDefinition Height="28"/>                                           
                                        </Grid.RowDefinitions>

                                        <Grid.ColumnDefinitions>
                                            <ColumnDefinition Width="30*"/>
                                            <ColumnDefinition Width="25*"/>
                                            <ColumnDefinition Width="25*"/> 
                                            <ColumnDefinition Width="20*"/> 
                                        </Grid.ColumnDefinitions>

                                       <Label
                                            Grid.Row="0"                                                          
                                            Grid.Column="0"
                                            VerticalOptions="Start"
                                            FontAttributes="None"                                       
                                            Text="{Binding ActivityName}"
                                            Margin="0,0,0,0"
                                            TextColor="Black"                                            
                                            Padding="0,10,0,0"
                                            FontFamily="Hiragino Sans"
                                            FontSize="14"
                                            HeightRequest="53"
                                            BackgroundColor="White"
                                       />
                                        <Label
                                            Grid.Row="0"                                                          
                                            Grid.Column="1"
                                            VerticalOptions="Center"
                                            FontAttributes="None"                                       
                                            Text="{Binding ActivityDuration}"
                                            TextColor="Black"
                                            Margin="0, 0,0, 0"
                                            Padding="0,10,0,0"
                                            FontFamily="Hiragino Sans"
                                            FontSize="14"
                                            HeightRequest="53"
                                            BackgroundColor="White"
                                       />
                                        <Label
                                            Grid.Row="0"                                                          
                                            Grid.Column="2"
                                            VerticalOptions="Center"
                                            FontAttributes="None"                                       
                                            Text="{Binding ActivityGoalDuration}"
                                            TextColor="Black"
                                            Margin="0, 0,0, 0"
                                            Padding="10,10,0,0"
                                            FontFamily="Hiragino Sans"
                                            FontSize="14"
                                            HeightRequest="53"
                                            BackgroundColor="White"
                                       />                                        
                                         <Switch
                                            Grid.Row="0"                                                          
                                            Grid.Column="3"
                                            VerticalOptions="Center"                                                                                                                            
                                            HeightRequest="53"
                                            BackgroundColor="White"
                                            IsToggled="{Binding ActivityEnabled}"
                                            Toggled="activitySwitch_Toggled"
                                            HorizontalOptions="EndAndExpand"
                                            Margin="0,0,0,0"
                                       />
                                    </Grid>

                                </StackLayout>
                            </ViewCell>
                        </DataTemplate>
                    </ListView.ItemTemplate>
                </ListView>

事件

 public void OnActivityTap(object sender, EventArgs e)
        {
            var item = (ViewCell)sender;
            UserActivities.Activities myactivitiesModel = item.BindingContext as 
            UserActivities.Activities;

            if (myactivitiesModel == null)
            {return;}
            foreach (var x in ViewModel.UserActivitiesList) {
                if(x.ActivityName == myactivitiesModel.ActivityName) {
                    mystopwatch.Start();
                    TimeSpan ts = myactivitiesModel.ActivityDuration;
                    ts = mystopwatch.Elapsed + ts;
                    x.ActivityDuration = mystopwatch.Elapsed + ts;
                }
}

Answer 1

我的问题是这样解决的：

                    //Create a new stopwatch
                    mystopwatch = new Stopwatch();
                    
                    //Add the current duration
                    TimeSpan ts = mystopwatch.Elapsed + x.ActivityDuration;

                    //Start stopwatch
                    mystopwatch.Start();

                    Device.StartTimer(TimeSpan.FromSeconds(seconds), () =>
                    {                        
                        x.ActivityDuration = (mystopwatch.Elapsed + ts);
                        OnPropertyChanged("ActivityDuration");
                        return true;
                    }
                    );