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[英]Xamarin Forms Update ListView on WillEnterForeground
[英]Xamarin forms ListView item dynamic update to GUI
我以 Xamarin 形式创建了一个 ListView 并绑定到视图模型中的 Observable 集合,通过调用 OnPropertyChanged 事件将项目动态添加到 ListView 工作正常。
但是在从服务获取状态更新后,我正在更新相应的 ListView 项目状态并调用 OnPropertyChanged 事件以及将 ListView 项目重新分配给它,但没有得到更新的 GUI 有时正常工作,有时没有。
下面是我完成的示例代码。
<ListView Grid.Row="3" HasUnevenRows="True" ItemsSource="{Binding ServiceList}" IsPullToRefreshEnabled="True" SeparatorColor="Black">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Orientation="Vertical" Spacing="4" Padding="5" BackgroundColor="LightGray">
<Label Text="{Binding OperationStatus, Converter={x:Static local:StatusMessageConverter.Default}}" FontSize="13" FontAttributes="Bold" TextColor="White" BackgroundColor="DarkCyan" />
<Label Text="{Binding Operation}" FontSize="10" Margin="10,0,0,0" />
<Label Text="{Binding OperationType}" FontSize="10" Margin="10,0,0,0" />
<Label Text="{Binding OperationStatus}" LineBreakMode="WordWrap" IsVisible="{Binding CanStatusVisible}" FontSize="10" Margin="10,0,0,0" />
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
public class ServiceViewModel : INotifyPropertyChanged
{
public ObservableCollection<ServiceItem> ServiceList
{
get
{
return _serviceList;
}
set
{
_serviceList = value;
OnPropertyChanged("ServiceList");
}
}
var tempList = new ObservableCollection<ServiceItem>();
tempList = ServiceList;
var targetItem = from item in tempList
where item.UniqueId == uniqueId
select item;
if (targetItem.Any())
{
var resultItem = targetItem.FirstOrDefault();
resultItem.CanStatusVisible = true;
resultItem.OperationStatus = string.Format("{0}: {1}", "Status Message", resultMessage);
}
ServiceList = null;
ServiceList = tempList;
OnPropertyChanged("ServiceList");
}
public class ServiceItem
{
public string UniqueId { get; set; }
public string Operation { get; set; }
public string OperationType { get; set; }
public string OperationStatus { get; set; }
public string StatusMessage { get; set; }
public bool CanStatusVisible { get; set; }
}
确保您的模型类继承自INotifyPropertyChanged
接口(如上述评论中所述)。
public class ServiceItem :INotifyPropertyChanged
{
private string uniqueId,operation,operationType,operationStatus,statusMessage;
private bool statusVisible;
public string UniqueId { get { return uniqueId; } set { uniqueId= value; RaisePropertyChanged(nameof(UniqueId)); } }
public string Operation { get { return operation; } set { operation= value; RaisePropertyChanged(nameof(Operation)); } }
public string OperationType { get { return operationType; } set { operationType= value; RaisePropertyChanged(nameof(OperationType)); } }
public string OperationStatus { get { return operationStatus; } set { operationStatus= value; RaisePropertyChanged(nameof(OperationStatus)); } }
public string StatusMessage { get { return statusMessage; } set { statusMessage= value; RaisePropertyChanged(nameof(StatusMessage)); } }
public bool CanStatusVisible { get { return statusVisible; } set { statusVisible= value; RaisePropertyChanged(nameof(CanStatusVisible )); } }
}
那么您的 ViewModel 代码应该如下所示:
var tempList = new ObservableCollection<ServiceItem>();
tempList = ServiceList;
var targetItem = from item in tempList
where item.UniqueId == uniqueId
select item;
if (targetItem.Any())
{
var resultItem = targetItem.FirstOrDefault();
resultItem.CanStatusVisible = true;
resultItem.OperationStatus = string.Format("{0}: {1}", "Status Message", resultMessage);
}
ServiceList = null;
ServiceList = tempList;
完成这些更改后,您的代码应该可以工作
---澄清我对FreakyAli的好答案的评论---
FreakyAli 回答的重要部分是第一个代码片段:
public class ServiceItem :INotifyPropertyChanged
...
一旦完成,可以大大简化其他有问题的代码。 我认为(虽然我没有测试过)您可以将 Ali 在“那么您的 ViewModel 代码应该看起来像这样:”下显示的所有代码替换为:
ServiceItem resultItem = ServiceList.Where(item => item.UniqueId == uniqueId).FirstOrDefault();
if (resultItem != null)
{
resultItem.CanStatusVisible = true;
resultItem.OperationStatus = string.Format("{0}: {1}", "Status Message", resultMessage);
}
也就是说,不需要创建临时列表,也不需要操作ServiceList
。 当您更改ServiceItem
的属性时,该属性的RaisePropertyChanged
将触发所需的显示刷新。
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