如何在 MAUI 中创建类似的下拉菜单/选择。有什么可能的例子吗？我只需要为数据验证制作一个工具提示，以便它显示在所有类型元素的顶部，如 HTML 中的position:absolute;。但我在任何地方都找不到类似的东西。我只知道这应该通过自己的控件来完成
我使用第三方控件。而且我不明白他们是如何制作它们的。我想要一个小样本，或者有关如何操作的链接
任何信息和示例
您可以使用
Listview请参考以下代码：
public class ComboBox : StackLayout
{
private Entry _entry;
private ListView _listView;
private bool _supressFiltering;
private bool _supressSelectedItemFiltering;
//Bindable properties
public static readonly BindableProperty ListViewHeightRequestProperty = BindableProperty.Create(nameof(ListViewHeightRequest), typeof(double), typeof(ComboBox), defaultValue: null, propertyChanged: (bindable, oldVal, newVal) => {
var comboBox = (ComboBox)bindable;
comboBox._listView.HeightRequest = (double)newVal;
});
public double ListViewHeightRequest
{
get { return (double)GetValue(ListViewHeightRequestProperty); }
set { SetValue(ListViewHeightRequestProperty, value); }
}
public static readonly BindableProperty EntryBackgroundColorProperty = BindableProperty.Create(nameof(EntryBackgroundColor), typeof(Color), typeof(ComboBox), defaultValue: null, propertyChanged: (bindable, oldVal, newVal) => {
var comboBox = (ComboBox)bindable;
comboBox._entry.BackgroundColor = (Color)newVal;
});
public Color EntryBackgroundColor
{
get { return (Color)GetValue(EntryBackgroundColorProperty); }
set { SetValue(EntryBackgroundColorProperty, value); }
}
public static readonly BindableProperty EntryFontSizeProperty = BindableProperty.Create(nameof(EntryFontSize), typeof(double), typeof(ComboBox), defaultValue: null, propertyChanged: (bindable, oldVal, newVal) => {
var comboBox = (ComboBox)bindable;
comboBox._entry.FontSize = (double)newVal;
});
[TypeConverter(typeof(FontSizeConverter))]
public double EntryFontSize
{
get { return (double)GetValue(EntryFontSizeProperty); }
set { SetValue(EntryFontSizeProperty, value); }
}
public static readonly BindableProperty ItemsSourceProperty = BindableProperty.Create(nameof(ItemsSource), typeof(IEnumerable), typeof(ComboBox), defaultValue: null, propertyChanged: (bindable, oldVal, newVal) => {
var comboBox = (ComboBox)bindable;
comboBox._listView.ItemsSource = (IEnumerable)newVal;
});
public IEnumerable ItemsSource
{
get { return (IEnumerable)GetValue(ItemsSourceProperty); }
set { SetValue(ItemsSourceProperty, value); }
}
public static readonly BindableProperty SelectedItemProperty = BindableProperty.Create(nameof(SelectedItem), typeof(object), typeof(ComboBox), defaultValue: null, propertyChanged: (bindable, oldVal, newVal) => {
var comboBox = (ComboBox)bindable;
comboBox._listView.SelectedItem = newVal;
});
public object SelectedItem
{
get { return (object)GetValue(SelectedItemProperty); }
set { SetValue(SelectedItemProperty, value); }
}
public static new readonly BindableProperty VisualProperty = BindableProperty.Create(nameof(Visual), typeof(IVisual), typeof(ComboBox), defaultValue: new DefaultVisual(), propertyChanged: (bindable, oldVal, newVal) => {
var comboBox = (ComboBox)bindable;
comboBox._listView.Visual = (IVisual)newVal;
comboBox._entry.Visual = (IVisual)newVal;
});
public new IVisual Visual
{
get { return (IVisual)GetValue(VisualProperty); }
set { SetValue(VisualProperty, value); }
}
public static readonly BindableProperty PlaceholderProperty = BindableProperty.Create(nameof(Placeholder), typeof(string), typeof(ComboBox), defaultValue: "", propertyChanged: (bindable, oldVal, newVal) => {
var comboBox = (ComboBox)bindable;
comboBox._entry.Placeholder = (string)newVal;
});
public string Placeholder
{
get { return (string)GetValue(PlaceholderProperty); }
set { SetValue(PlaceholderProperty, value); }
}
public static readonly BindableProperty TextProperty = BindableProperty.Create(nameof(Text), typeof(string), typeof(ComboBox), defaultValue: "", propertyChanged: (bindable, oldVal, newVal) => {
var comboBox = (ComboBox)bindable;
comboBox._entry.Text = (string)newVal;
});
public string Text
{
get { return (string)GetValue(TextProperty); }
set { SetValue(TextProperty, value); }
}
public static readonly BindableProperty ItemTemplateProperty = BindableProperty.Create(nameof(ItemTemplate), typeof(DataTemplate), typeof(ComboBox), defaultValue: null, propertyChanged: (bindable, oldVal, newVal) => {
var comboBox = (ComboBox)bindable;
comboBox._listView.ItemTemplate = (DataTemplate)newVal;
});
public DataTemplate ItemTemplate
{
get { return (DataTemplate)GetValue(ItemTemplateProperty); }
set { SetValue(ItemTemplateProperty, value); }
}
public static readonly BindableProperty EntryDisplayPathProperty = BindableProperty.Create(nameof(EntryDisplayPath), typeof(string), typeof(ComboBox), defaultValue: "");
public string EntryDisplayPath
{
get { return (string)GetValue(EntryDisplayPathProperty); }
set { SetValue(EntryDisplayPathProperty, value); }
}
public event EventHandler<SelectedItemChangedEventArgs> SelectedItemChanged;
protected virtual void OnSelectedItemChanged(SelectedItemChangedEventArgs e)
{
EventHandler<SelectedItemChangedEventArgs> handler = SelectedItemChanged;
handler?.Invoke(this, e);
}
public event EventHandler<TextChangedEventArgs> TextChanged;
protected virtual void OnTextChanged(TextChangedEventArgs e)
{
EventHandler<TextChangedEventArgs> handler = TextChanged;
handler?.Invoke(this, e);
}
public ComboBox()
{
//Entry used for filtering list view
_entry = new Entry();
_entry.Margin = new Thickness(0);
_entry.Keyboard = Keyboard.Create(KeyboardFlags.None);
_entry.Focused += (sender, args) => _listView.IsVisible = true;
_entry.Unfocused += (sender, args) => _listView.IsVisible = false;
//Text changed event, bring it back to the surface
_entry.TextChanged += (sender, args) =>
{
if (_supressFiltering)
return;
if (String.IsNullOrEmpty(args.NewTextValue))
{
_supressSelectedItemFiltering = true;
_listView.SelectedItem = null;
_supressSelectedItemFiltering = false;
}
_listView.IsVisible = true;
OnTextChanged(args);
};
//List view - used to display search options
_listView = new ListView();
_listView.IsVisible = false;
_listView.Margin = new Thickness(0);
Microsoft.Maui.Controls.PlatformConfiguration.iOSSpecific.ListView.SetSeparatorStyle(_listView, Microsoft.Maui.Controls.PlatformConfiguration.iOSSpecific.SeparatorStyle.FullWidth);
_listView.HeightRequest = 100;
_listView.HorizontalOptions = LayoutOptions.StartAndExpand;
_listView.SetBinding(ListView.SelectedItemProperty, new Binding(nameof(ComboBox.SelectedItem), source: this));
//Item selected event, surface it back to the top
_listView.ItemSelected += (sender, args) =>
{
if (!_supressSelectedItemFiltering)
{
_supressFiltering = true;
var selectedItem = args.SelectedItem;
_entry.Text = !String.IsNullOrEmpty(EntryDisplayPath) && selectedItem != null ? selectedItem.GetType().GetProperty(EntryDisplayPath).GetValue(selectedItem, null).ToString() : selectedItem?.ToString();
_supressFiltering = false;
_listView.IsVisible = false;
OnSelectedItemChanged(args);
_entry.Unfocus();
}
};
//Add bottom border
var boxView = new BoxView();
boxView.HeightRequest = 1;
boxView.Color = Colors.Black;
boxView.Margin = new Thickness(0);
boxView.SetBinding(BoxView.IsVisibleProperty, new Binding(nameof(ListView.IsVisible), source: _listView));
Children.Add(_entry);
Children.Add(_listView);
Children.Add(boxView);
}
public new bool Focus()
{
return _entry.Focus();
}
public new void Unfocus()
{
_entry.Unfocus();
}
}
然后就可以在后面的代码中设置itemsource了：
combobox.ItemsSource = new List<string>() { "item1", "item2", "item3", "item4", "item5","item6" };
并在xaml中使用它：
<local:ComboBox x:Name="combobox" SelectedItemChanged="combobox_SelectedItemChanged"/>