【发布时间】：2020-05-12 18:12:38
【问题描述】：
我有一个 xamarin.forms 应用程序，它有一个列表视图，显示从 firebase 获取的项目。我面临的问题是 SO 中提出的问题，即；我在列表视图中的一项（名为 location 的项目）仅在我们滚动列表视图时更新。我试图实现iNotifyPropertychanged，但我仍然面临同样的问题。我在这里做错了什么？任何帮助都会得到帮助。
我的 Listview 项目来源设置
var person = await firebaseHelper.GetPerson(EmployeeID);// getting data from firebase
LocationData = person.userdata.Where(x => DateTime.Parse(x.DateTime).ToString("yyyy-MM-dd") == StartDate.Date.ToString("yyyy-MM-dd") && x.Longitude != "initial").ToList();
ObservableCollection<UserLocationData> dynamicLocation = new ObservableCollection<UserLocationData>(LocationData);
TrackingListView.ItemsSource = dynamicLocation;
if (dynamicLocation.Count != 0)
{
foreach (UserLocationData Item in dynamicLocation)
{
Item.DateTime = DateTime.Parse(Item.DateTime).ToString("MMMM dd,yyyy hh:mm tt");
if (!string.IsNullOrEmpty(Item.Latitude) && !string.IsNullOrEmpty(Item.Longitude))
{
var Locations = await Geocoding.GetPlacemarksAsync(Convert.ToDouble(Item.Latitude), Convert.ToDouble(Item.Longitude));
var placemark = Locations?.FirstOrDefault();
if (placemark.Thoroughfare.ToString() != null)
{
var geocodeAddress =
placemark.Thoroughfare + '\n' +
placemark.SubAdminArea + '\n';
Item.Location = geocodeAddress.ToString();
}
else
{
Item.Location = Item.Latitude + "," + Item.Longitude;
}
}
}
我的数据模型
public class Person : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
public string Name { get; set; }
public string PersonId { get; set; }
public string Address { get; set; }
public string PhoneNumber { get; set; }
public string EmailID { get; set; }
public string Password { get; set; }
public bool Status { get; set; }
public bool IsAdmin { get; set; }
public List<UserLocationData> userdata { get; set; }
}
public partial class UserLocationData : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
public string Latitude { get; set; }
public string Longitude { get; set; }
public string DateTime { get; set; }
private string _location;
public string Location
{
get
{
return _location;
}
set
{
if (value != null)
{
_location = value;
NotifyPropertyChanged("Selected");
}
}
}
public bool ButtonOn { get; set; }
public bool ButtonOff { get; set; }
}
Firebase GetPerson 部分
public async Task<Person> GetPerson(string personId)
{
var allPersons = await GetAllPersons();
await firebase
.Child("Persons")
.OnceAsync<Person>();
return allPersons.Where(a => a.PersonId == personId).FirstOrDefault();
}
我的 XAML
<ListView x:Name="TrackingListView" ItemsSource="{Binding} "
HasUnevenRows="True"
IsVisible="False"
CachingStrategy="RecycleElement"
SeparatorVisibility="None"
SelectionMode="None"
BackgroundColor="Transparent"
Margin="10,10,10,10"
HorizontalOptions="FillAndExpand"
>
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<ViewCell.View>
<Frame
Padding="5"
Margin="0,5,0,5"
Opacity="0.9"
BackgroundColor="White"
BorderColor="LightBlue"
HasShadow="True"
CornerRadius="10"
ClassId="{Binding DateTime}"
HorizontalOptions="FillAndExpand">
<Frame.GestureRecognizers>
<TapGestureRecognizer Tapped="TapGestureRecognizer_Tapped"></TapGestureRecognizer>
</Frame.GestureRecognizers>
<Grid Margin="0,10,0,0" >
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<StackLayout HorizontalOptions="FillAndExpand" Grid.Row="0" Grid.Column="0" Orientation="Horizontal">
<Image Source="clock.png" HorizontalOptions="Start" VerticalOptions="Start"
HeightRequest="20" Margin="10,0,5,0"
></Image>
<StackLayout Orientation="Vertical" Margin="0" HorizontalOptions="FillAndExpand">
<Label Text="Location fetched time" FontSize="12" HorizontalOptions="StartAndExpand" VerticalOptions="Center"
TextColor="Blue"
></Label>
<Label Text="{Binding DateTime}" HorizontalOptions="StartAndExpand" VerticalOptions="Center"
TextColor="Black" FontSize="Small"
></Label>
</StackLayout>
</StackLayout>
<StackLayout Grid.Column="1" Grid.Row="0" HorizontalOptions="EndAndExpand" VerticalOptions="FillAndExpand">
<Image Source="googlemap.png" HorizontalOptions="End" VerticalOptions="Center" HeightRequest="30" ></Image>
</StackLayout>
<StackLayout HorizontalOptions="FillAndExpand" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2" Orientation="Horizontal">
<Image Source="currentlocation.png" HorizontalOptions="Start" VerticalOptions="Start"
HeightRequest="20" Margin="10,0,5,0"
></Image>
<StackLayout Orientation="Vertical" Margin="0" HorizontalOptions="FillAndExpand">
<Label Text="Location " FontSize="12" HorizontalOptions="StartAndExpand" VerticalOptions="Center"
TextColor="Blue"
></Label>
<Label Text="{Binding Location}" HorizontalOptions="StartAndExpand" VerticalOptions="Center"
TextColor="Black" FontSize="Small"
></Label>
</StackLayout>
</StackLayout>
<StackLayout Grid.Row="2" Grid.Column="0" Grid.ColumnSpan="2" Margin="0" >
<Grid>
<StackLayout Orientation="Horizontal" Margin="0" IsVisible="{Binding ButtonOn}">
<Image Source="start.png" HorizontalOptions="Start"
HeightRequest="20" Margin="10,0,5,0"
VerticalOptions="Start">
</Image>
<Label Text="Location Tracking Started" VerticalOptions="Center" TextColor="Green" FontSize="12" ></Label>
</StackLayout>
<StackLayout Orientation="Horizontal" Margin="0" IsVisible="{Binding ButtonOff}">
<Image Source="stop.png" HorizontalOptions="Start"
HeightRequest="20" Margin="10,0,5,0"
VerticalOptions="Start">
</Image>
<Label Text="Location Tracking Stopped" VerticalOptions="Center" TextColor="Red" FontSize="12" ></Label>
</StackLayout>
</Grid>
</StackLayout>
</Grid>
</Frame>
</ViewCell.View>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
【问题讨论】：
-
如何获取位置数据？使用 Firebase 数据库？尝试在 if 语句之后设置 ListView Itemsource。根据我在 firebase 数据库中获取数据并最终设置 ItemSource 的测试，它对我来说效果很好。
-
@WendyZang-MSFT 兄弟。谢谢您的回复。我每次都可以从firebase获取数据。没问题。实际上，我从firebase获得了纬度和经度，我尝试将其转换为地址并将其绑定到“Item.Location”。问题是第一次数据会正确显示，如果我们重新加载列表，位置参数将不会显示。它只会在我们滚动时显示。当我放置调试器时，它每次都会显示数据。但不在列表视图上绘画
-
知道了。我会对此进行测试，并尽快反馈。
-
@WendyZang-MSFT 谢谢兄弟...
-
NotifyPropertyChanged("Selected");应该是NotifyPropertyChanged("Location");
标签： firebase xamarin xamarin.forms