Joe*_*ano 6 c# xaml listview xamarin xamarin.forms
我在a中显示了一个SQLite对象列表ListView,但我想让它们水平显示.所以不是这样的:
| longitem |
| item |
| evenlongeritem |
| item |
| longeritem |
我要这个:
| longitem item |
| evenlongeritem |
| item longeritem |
重要的是,这些项目的宽度可以不同,因此只需将列表分成一定数量的列就可以得到改进,但并不理想.我也不知道物品的数量.
这是我目前的代码:
<ListView x:Name="inactiveList" VerticalOptions="Start" ItemTapped="PutBack">
<ListView.ItemTemplate>
<DataTemplate>
<TextCell Text="{Binding Name}" TextColor="Black">
<TextCell.ContextActions>
<MenuItem Command="{Binding Source={x:Reference ListPage}, Path=DeleteListItem}" CommandParameter="{Binding .}" Text="delete" />
</TextCell.ContextActions>
</TextCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
代码背后:
public ListPage()
{
InitializeComponent();
ObservableCollection<ListItem> activeItems =
new ObservableCollection<ListItem>(
App.ListItemRepo.GetActiveListItems());
activeList.ItemsSource = activeItems;
...
我尝试将其包裹ViewCell在横向StackLayout,但我收到此错误:
未处理的异常:System.InvalidCastException:指定的强制转换无效.
我不确定那个错误意味着什么,但我认为不可能在StackLayout内部添加一个DataTemplate.我也做不了ListView水平.
-
我终于可以将简单的标签水平列出,但现在我无法重新创建垂直ListView内置的水龙头和长按动作.这可能吗？
ListView.xaml
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns:local="clr-namespace:Myapp">
<!-- ... -->
<local:WrapLayout x:Name="inactiveList" ItemsSource="{Binding .}" Spacing="5" />
ListView.xaml.cs
using Myapp.Models;
using System;
using System.Collections.ObjectModel;
using System.Collections.Generic;
using System.Linq;
using SQLite;
using System.Threading.Tasks;
using System.IO;
using Xamarin.Forms;
using System.Diagnostics;
using DLToolkit.Forms.Controls;
namespace Myapp
{
public partial class ListPage
{
...
public ListPage()
{
InitializeComponent();
ObservableCollection<ListItem> inactiveItems =
new ObservableCollection<ListItem>(
App.ListItemRepo.GetInactiveListItems());
inactiveList.ItemsSource = inactiveItems;
inactiveList.HeightRequest = 50 * inactiveItems.Count;
}
...
}
public class WrapLayout : Layout<View>
{
public ObservableCollection<ListItem> ItemsSource
{
get { return (ObservableCollection<ListItem>)GetValue(ItemSourceProperty); }
set { SetValue(ItemSourceProperty, value); }
}
public static readonly BindableProperty ItemSourceProperty =
BindableProperty.Create
(
"ItemsSource",
typeof(ObservableCollection<ListItem>),
typeof(WrapLayout),
propertyChanged: (bindable, oldvalue, newvalue) => ((WrapLayout)bindable).AddViews()
);
void AddViews()
{
Children.Clear();
foreach (ListItem s in ItemsSource)
{
Button button = new Button();
button.BackgroundColor = Color.Red;
button.Text = s.Name;
button.TextColor = Color.Black;
button.Clicked = "{Binding Source={x:Reference ListPage}, Path=PutBack}";
Children.Add(button);
}
}
public static readonly BindableProperty SpacingProperty =
BindableProperty.Create
(
"Spacing",
typeof(double),
typeof(WrapLayout),
10.0,
propertyChanged: (bindable, oldvalue, newvalue) => ((WrapLayout)bindable).OnSizeChanged()
);
public double Spacing
{
get { return (double)GetValue(SpacingProperty); }
set { SetValue(SpacingProperty, value); }
}
private void OnSizeChanged()
{
this.ForceLayout();
}
protected override SizeRequest OnMeasure(double widthConstraint, double heightConstraint)
{
if (WidthRequest > 0)
widthConstraint = Math.Min(widthConstraint, WidthRequest);
if (HeightRequest > 0)
heightConstraint = Math.Min(heightConstraint, HeightRequest);
double internalWidth = double.IsPositiveInfinity(widthConstraint) ? double.PositiveInfinity : Math.Max(0, widthConstraint);
double internalHeight = double.IsPositiveInfinity(heightConstraint) ? double.PositiveInfinity : Math.Max(0, heightConstraint);
return DoHorizontalMeasure(internalWidth, internalHeight);
}
private SizeRequest DoHorizontalMeasure(double widthConstraint, double heightConstraint)
{
int rowCount = 1;
double width = 0;
double height = 0;
double minWidth = 0;
double minHeight = 0;
double widthUsed = 0;
foreach (var item in Children)
{
var size = item.Measure(widthConstraint, heightConstraint);
height = Math.Max(height, size.Request.Height);
var newWidth = width + size.Request.Width + Spacing;
if (newWidth > widthConstraint)
{
rowCount++;
widthUsed = Math.Max(width, widthUsed);
width = size.Request.Width;
}
else
width = newWidth;
minHeight = Math.Max(minHeight, size.Minimum.Height);
minWidth = Math.Max(minWidth, size.Minimum.Width);
}
if (rowCount > 1)
{
width = Math.Max(width, widthUsed);
height = (height + Spacing) * rowCount - Spacing; // via MitchMilam
}
return new SizeRequest(new Size(width, height), new Size(minWidth, minHeight));
}
protected override void LayoutChildren(double x, double y, double width, double height)
{
double rowHeight = 0;
double yPos = y, xPos = x;
foreach (var child in Children.Where(c => c.IsVisible))
{
var request = child.Measure(width, height);
double childWidth = request.Request.Width;
double childHeight = request.Request.Height;
rowHeight = Math.Max(rowHeight, childHeight);
if (xPos + childWidth > width)
{
xPos = x;
yPos += rowHeight + Spacing;
rowHeight = 0;
}
var region = new Rectangle(xPos, yPos, childWidth, childHeight);
LayoutChildIntoBoundingRegion(child, region);
xPos += region.Width + Spacing;
}
}
}
}
请参阅我的帖子.它与你的情况类似.
只需要定制Layout和管理它的大小和孩子的安排.
我得到一个"类型本地:在xmlns clr-namespace:Myapp中找不到WrapLayout"错误.
将类WrapLayout 公开,将其分开ListPage.
我对这里如何应用数据绑定也有点困惑
我们需要添加一个BindableProperty命名的ItemSource内部包装,并在属性更改时添加子视图.
Xmal位
<ContentPage.Content>
<local:WrapLayout x:Name="wrap" ItemSource="{Binding .}" Spacing="5" />
</ContentPage.Content>
代码背后
List<string> list = new List<string> {
"11111111111111111111111",
"22222",
"333333333333333",
"4",
"55555555",
"6666666666666666666666",
"77777",
"8888888888",
"99999999999999999999999999999999"
};
this.BindingContext = list;
我们可以定义event内部WrapLayout,当我们点击或长按按钮时,触发事件.关于长按,我们应该创建自定义渲染器来实现它.
namespace ImageWrapLayout
{
public class ButtonWithLongPressGesture : Button
{
public EventHandler LongPressHandle;
public EventHandler TapHandle;
public void HandleLongPress(object sender, EventArgs e)
{
//Handle LongPressActivated Event
LongPressHandle(sender, e);
}
public void HandleTap(object sender, EventArgs e)
{
//Handle Tap Event
TapHandle(sender, e);
}
}
public class WrapLayout : Layout<View>
{
public List<string> ItemSource
{
get { return (List<string>)GetValue(ItemSourceProperty); }
set { SetValue(ItemSourceProperty, value); }
}
public static readonly BindableProperty ItemSourceProperty =
BindableProperty.Create
(
"ItemSource",
typeof(List<string>),
typeof(WrapLayout),
propertyChanged: (bindable, oldvalue, newvalue) => ((WrapLayout)bindable).AddViews()
);
void AddViews()
{
Children.Clear();
foreach (string s in ItemSource)
{
ButtonWithLongPressGesture button = new ButtonWithLongPressGesture();
button.BackgroundColor = Color.Red;
button.Text = s;
button.TextColor = Color.Black;
Children.Add(button);
button.TapHandle += WrapLayoutTapHandle;
button.LongPressHandle = WrapLayoutLongPressHandle;
}
}
public EventHandler WrapLayoutLongPressHandle;
public EventHandler WrapLayoutTapHandle;
public static readonly BindableProperty SpacingProperty =
BindableProperty.Create
(
"Spacing",
typeof(double),
typeof(WrapLayout),
10.0,
propertyChanged: (bindable, oldvalue, newvalue) => ((WrapLayout)bindable).OnSizeChanged()
);
public double Spacing
{
get { return (double)GetValue(SpacingProperty); }
set { SetValue(SpacingProperty, value); }
}
private void OnSizeChanged()
{
this.ForceLayout();
}
protected override SizeRequest OnMeasure(double widthConstraint, double heightConstraint)
{
if (WidthRequest > 0)
widthConstraint = Math.Min(widthConstraint, WidthRequest);
if (HeightRequest > 0)
heightConstraint = Math.Min(heightConstraint, HeightRequest);
double internalWidth = double.IsPositiveInfinity(widthConstraint) ? double.PositiveInfinity : Math.Max(0, widthConstraint);
double internalHeight = double.IsPositiveInfinity(heightConstraint) ? double.PositiveInfinity : Math.Max(0, heightConstraint);
return DoHorizontalMeasure(internalWidth, internalHeight);
}
private SizeRequest DoHorizontalMeasure(double widthConstraint, double heightConstraint)
{
int rowCount = 1;
double width = 0;
double height = 0;
double minWidth = 0;
double minHeight = 0;
double widthUsed = 0;
foreach (var item in Children)
{
var size = item.Measure(widthConstraint, heightConstraint);
height = Math.Max(height, size.Request.Height);
var newWidth = width + size.Request.Width + Spacing;
if (newWidth > widthConstraint)
{
rowCount++;
widthUsed = Math.Max(width, widthUsed);
width = size.Request.Width;
}
else
width = newWidth;
minHeight = Math.Max(minHeight, size.Minimum.Height);
minWidth = Math.Max(minWidth, size.Minimum.Width);
}
if (rowCount > 1)
{
width = Math.Max(width, widthUsed);
height = (height + Spacing) * rowCount - Spacing; // via MitchMilam
}
return new SizeRequest(new Size(width, height), new Size(minWidth, minHeight));
}
protected override void LayoutChildren(double x, double y, double width, double height)
{
double rowHeight = 0;
double yPos = y, xPos = x;
foreach (var child in Children.Where(c => c.IsVisible))
{
var request = child.Measure(width, height);
double childWidth = request.Request.Width;
double childHeight = request.Request.Height;
rowHeight = Math.Max(rowHeight, childHeight);
if (xPos + childWidth > width)
{
xPos = x;
yPos += rowHeight + Spacing;
rowHeight = 0;
}
var region = new Rectangle(xPos, yPos, childWidth, childHeight);
LayoutChildIntoBoundingRegion(child, region);
xPos += region.Width + Spacing;
}
}
}
}
[assembly: ExportRenderer(typeof(ButtonWithLongPressGesture), typeof(LongPressGestureRecognizerButtonRenderer))]
namespace ImageWrapLayout.iOS
{
class LongPressGestureRecognizerButtonRenderer : ButtonRenderer
{
ButtonWithLongPressGesture view;
public LongPressGestureRecognizerButtonRenderer()
{
this.AddGestureRecognizer(new UILongPressGestureRecognizer((longPress) => {
if (longPress.State == UIGestureRecognizerState.Began)
{
view.HandleLongPress(view, new EventArgs());
}
}));
}
protected override void OnElementChanged(ElementChangedEventArgs<Button> e)
{
base.OnElementChanged(e);
if (e.NewElement != null)
view = e.NewElement as ButtonWithLongPressGesture;
//if(Control == null)
//{
UIButton but = Control as UIButton;
but.TouchUpInside += (sender, e1) => {
view.HandleTap(view, new EventArgs());
};
//}
}
}
}
inactiveList.WrapLayoutLongPressHandle += (sender, e) =>
{
};
inactiveList.WrapLayoutTapHandle += (sender, e) =>
{
};