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using System.Collections.Generic;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Threading.Tasks;
namespace Xamarin.Forms.Pages
{
public abstract class BaseDataSource : IDataSource, INotifyPropertyChanged
{
readonly DataSourceList _dataSourceList = new DataSourceList();
bool _initialized;
bool _isLoading;
public IReadOnlyList<IDataItem> Data
{
get
{
#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
Initialize();
#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
return _dataSourceList;
}
}
public bool IsLoading
{
get { return _isLoading; }
set
{
if (_isLoading == value)
return;
_isLoading = value;
OnPropertyChanged();
}
}
#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
public object this[string key]
{
get
{
Initialize();
return GetValue(key);
}
set
{
Initialize();
if (SetValue(key, value))
OnKeyChanged(key);
}
}
#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
IEnumerable<string> IDataSource.MaskedKeys => _dataSourceList.MaskedKeys;
async void IDataSource.MaskKey(string key)
{
await Initialize();
_dataSourceList.MaskKey(key);
}
async void IDataSource.UnmaskKey(string key)
{
await Initialize();
_dataSourceList.UnmaskKey(key);
}
event PropertyChangedEventHandler INotifyPropertyChanged.PropertyChanged
{
add { PropertyChanged += value; }
remove { PropertyChanged -= value; }
}
protected abstract Task<IList<IDataItem>> GetRawData();
protected abstract object GetValue(string key);
protected void OnPropertyChanged([CallerMemberName] string property = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(property));
}
protected abstract bool SetValue(string key, object value);
async Task Initialize()
{
// Do this lazy because GetRawData is virtual and calling it in the ctor is therefor unfriendly
if (_initialized)
return;
_initialized = true;
IList<IDataItem> rawData = await GetRawData();
if (!(rawData is INotifyCollectionChanged))
{
Log.Warning("Xamarin.Forms.Pages", "DataSource does not implement INotifyCollectionChanged, updates will not be reflected");
rawData = rawData.ToList(); // Make a copy so we can be sure this list wont change out from under us
}
_dataSourceList.MainList = rawData;
// Test if INPC("Item") is enough to trigger a full reset rather than triggering a new event for each key?
foreach (IDataItem dataItem in rawData)
{
OnKeyChanged(dataItem.Name);
}
}
void OnKeyChanged(string key)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs($"Item[{key}]"));
}
event PropertyChangedEventHandler PropertyChanged;
}
}
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