using System; using System.Globalization; using System.Threading.Tasks; namespace Xamarin.Forms.Pages { public class DataSourceBinding : BindingBase { internal const string SelfPath = "."; IValueConverter _converter; object _converterParameter; WeakReference _dataSourceRef; BindingExpression _expression; string _path; public DataSourceBinding() { } public DataSourceBinding(string path, BindingMode mode = BindingMode.Default, IValueConverter converter = null, object converterParameter = null, string stringFormat = null) { if (path == null) throw new ArgumentNullException(nameof(path)); if (string.IsNullOrWhiteSpace(path)) throw new ArgumentException("path can not be an empty string", nameof(path)); AllowChaining = true; Path = path; Converter = converter; ConverterParameter = converterParameter; Mode = mode; StringFormat = stringFormat; } public IValueConverter Converter { get { return _converter; } set { ThrowIfApplied(); _converter = value; } } public object ConverterParameter { get { return _converterParameter; } set { ThrowIfApplied(); _converterParameter = value; } } public string Path { get { return _path; } set { ThrowIfApplied(); _path = value; _expression = GetBindingExpression($"DataSource[{value}]"); } } internal override void Apply(bool fromTarget) { base.Apply(fromTarget); if (_expression == null) _expression = new BindingExpression(this, SelfPath); _expression.Apply(fromTarget); } internal override async void Apply(object newContext, BindableObject bindObj, BindableProperty targetProperty) { var view = bindObj as VisualElement; if (view == null) throw new InvalidOperationException(); base.Apply(newContext, bindObj, targetProperty); Element dataSourceParent = await FindDataSourceParentAsync(view); var dataSourceProviderer = (IDataSourceProvider)dataSourceParent; if (dataSourceProviderer != null) _dataSourceRef = new WeakReference(dataSourceProviderer); dataSourceProviderer?.MaskKey(_path); ApplyInner(dataSourceParent, bindObj, targetProperty); } internal override BindingBase Clone() { return new DataSourceBinding(Path, Mode) { Converter = Converter, ConverterParameter = ConverterParameter, StringFormat = StringFormat }; } internal override object GetSourceValue(object value, Type targetPropertyType) { if (Converter != null) value = Converter.Convert(value, targetPropertyType, ConverterParameter, CultureInfo.CurrentUICulture); return base.GetSourceValue(value, targetPropertyType); } internal override object GetTargetValue(object value, Type sourcePropertyType) { if (Converter != null) value = Converter.ConvertBack(value, sourcePropertyType, ConverterParameter, CultureInfo.CurrentUICulture); return base.GetTargetValue(value, sourcePropertyType); } internal override void Unapply() { base.Unapply(); if (_dataSourceRef != null && _dataSourceRef.IsAlive) { var dataSourceProviderer = (IDataSourceProvider)_dataSourceRef.Target; dataSourceProviderer?.UnmaskKey(_path); } _expression?.Unapply(); } void ApplyInner(Element templatedParent, BindableObject bindableObject, BindableProperty targetProperty) { if (_expression == null && templatedParent != null) _expression = new BindingExpression(this, SelfPath); _expression?.Apply(templatedParent, bindableObject, targetProperty); } static async Task FindDataSourceParentAsync(Element element) { while (!Application.IsApplicationOrNull(element)) { if (element is IDataSourceProvider) return element; element = await TemplateUtilities.GetRealParentAsync(element); } return null; } BindingExpression GetBindingExpression(string path) { return new BindingExpression(this, !string.IsNullOrWhiteSpace(path) ? path : SelfPath); } } }