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InotifyPropertiesChanged列表视图

cross-platform xamarin.forms listview c#
  •  1
  • Usman Zafer  · 技术社区  · 6 年前

    我刚接触过Xamarin表单,并尝试在我的应用程序中实现无限循环功能。我所遵循的示例代码运行良好,我已成功地将其集成到我的应用程序中。

    问题是我无法找出如何从代码中更改ListView的源代码。

    我打算在我的ListView上面使用按钮(如下图所示),单击后,ListView的源代码将发生更改。

    这就是我的代码的样子 

    <contentpage.bindingContext>
<local:主视图模型/>
</contentpage.bindingContext>

<堆叠布局>

<listview x:name=“tyres_listview”itemssource=“绑定项”
hasUnevenRows=“true”SeparatorVisibility=“none”>

<listview.behaviors>
<extended:无限滚动行为isloadingmore=“绑定忙”/>
</listview.behaviors>
<listview.itemtemplate>

<数据模板>
<查看单元格>

<堆叠布局>
<grid margin=“10”VerticalOptions=“FillAndExpand”HorizontalOptions=“FillAndExpand”>
<grid.columndefinitions>
<columnDefinition width=“0.25*”></columnDefinition>

<columnDefinition width=“0.75*”></columnDefinition>
</grid.columndefinitions>

<stacklayout grid.column=“0”horizontaloptions=“fillandexpand”verticalocations=“fillandexpand”margin=“5,5,5,10”>
<image source=“绑定图像_url”>
&图像/GT;
</stacklayout>
<stacklayout grid.column=“1”spacing=“0”>
<label text=“绑定名称”fontattributes=“bold”fontsize=“small”margin=“0,5,5,0”VerticalOptions=“Center”></label>
<label text=“绑定品牌”verticaloptions=“center”fontsize=“micro”></label>
<label text=“绑定项目_id”verticaloptions=“center”fontsize=“micro”></label>

<stacklayout orientation=“horizontal”x:name=“sl_db”>
<image source=“fuel.png”></image>
<label text=“绑定燃料类型”></label>
<image source=“weather.png”></image>
<label text=“绑定Wheather类型”></label>
<image source=“volume.png”></image>
<label text=“绑定噪音”></label>
<label text=“db”></label>
</stacklayout>


<stacklayout orientation=“水平”>
<image></image>
<label text=“绑定额定值”></label>
</stacklayout>

<stacklayout orientation=“水平”>
<label text=“price:”VerticalOptions=“Center”></label>
<label text=“绑定价格”verticaloptions=“center”textcolor=“green”></label>
<label text=“eur”VerticalOptions=“Center”></label>

</stacklayout>
<stacklayout orientation=“水平”>
<stacklayout.gesturerecognizers>
<TapGestureRecognizer tapped=“TapGestureRecognizer tapped_1”>

</TapGestureRecognizer>
</stacklayout.gesturerecognizers>
<stacklayout backgroundcolor=“red”orientation=“horizontal”margin=“5”>
<image source=“shoppingcart.png”margin=“10,0,0,0”></image>
<label text=“Add to Cart”verticaloptions=“center”horizontaloptions=“endExpand”margin=“0,0,10,0”></label>
</stacklayout>
<image x:name=“button_info”source=“info.png”>

<image.gesturerecognizers>
<TapGestureRecognizer tapped=“button ou info ou clicked”></TapGestureRecognizer>
</image.gesturerecognizers>

&图像/GT;
</stacklayout>

</stacklayout>

和/格栅& GT;
</stacklayout>

</viewcell>

</datatemplate>

</listview.itemtemplate>

<listview.footer>
<grid padding=“6”isvisible=“绑定忙”>
&!--将页脚设置为不可见时高度为零-->
<grid.triggers>
<trigger targettype=“grid”property=“isvisible”value=“false”>
<setter property=“heightrequest”value=“0”/>
</trigger>
</grid.triggers>
&!--加载内容-->
<label text=“loading…”textcolor=“deeplink”fontsize=“20”fontattributes=“bold”verticaloptions=“center”horizontaloptions=“center”/>gt;
和/格栅& GT;
</listview.footer>
</listview>
<button clicked=“button_change_order_clicked”></button>
</stacklayout>
< /代码> 


    


    public class mainviewModel:InotifyPropertyChanged
{
私人旅馆很忙;
private const int pagesize=10;
readonly dataservice_dataservice=new dataservice();

公共无限滚动集合<product_search>项get;

公共布尔正忙
{
get=>\u正忙;
设置
{
_ IsBusy=值;
onPropertyChanged();
}
}
公共主视图模型()
{
items=新的无限滚动集合<产品搜索>
{
onloadmore=async()=>
{
Is忙碌=真;

//加载下一页
var page=items.count/pagesize;
var items=await-dataservice.getitemsasync(page,pagesize);

Is忙碌=假;

//返回需要添加的项
退货项目;
},请
oncanloadMore=()=>
{
返回项目。计数<44;
}
};

downloadDataAsync();
}

私有异步任务下载数据异步()
{
var items=await-dataservice.getitemsasync(pageindex:0,pagesize:pagesize);
items.addrange(项);
}

公共事件propertychangedeventhandler propertychanged;

受保护的虚拟void OnPropertyChanged([CallerMemberName]String PropertyName=null)
{
属性已更改?.invoke(this,new propertychangedeventargs(propertyname));
}
}
< /代码> 


    }/P>


    任何帮助都是非常重要的。


    问题是我无法找出如何从代码中更改ListView的源代码。
    


    我打算在我的ListView上面使用按钮(如下图所示),单击后,ListView的源代码将发生更改。
    


    Image
    


    这就是我的代码的样子
    


     <ContentPage.BindingContext>
    <local:MainViewModel />
</ContentPage.BindingContext>

<StackLayout>

    <ListView  x:Name="tyres_listview" ItemsSource="{Binding Items}"
                       HasUnevenRows="True" SeparatorVisibility="None"  >

        <ListView.Behaviors>
            <extended:InfiniteScrollBehavior IsLoadingMore="{Binding IsBusy}" />
        </ListView.Behaviors>
        <ListView.ItemTemplate>

            <DataTemplate>
                <ViewCell>

                    <StackLayout>
                        <Grid Margin="10" VerticalOptions="FillAndExpand" HorizontalOptions="FillAndExpand">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="0.25*"></ColumnDefinition>

                                <ColumnDefinition Width="0.75*"></ColumnDefinition>
                            </Grid.ColumnDefinitions>

                            <StackLayout  Grid.Column="0" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" Margin="5,5,5,10">
                                <Image  Source="{Binding image_url}"  >
                                </Image>
                            </StackLayout>
                            <StackLayout Grid.Column="1" Spacing="0" >
                                <Label Text="{Binding name}" FontAttributes="Bold" FontSize="Small" Margin="0,5,5,0" VerticalOptions="Center" ></Label>
                                <Label  Text="{Binding brand}" VerticalOptions="Center" FontSize="Micro"  ></Label>
                                <Label  Text="{Binding item_id}" VerticalOptions="Center" FontSize="Micro"  ></Label>

                                <StackLayout Orientation="Horizontal" x:Name="sl_db" >
                                    <Image Source="fuel.png" ></Image>
                                    <Label Text="{Binding fuel_type}"></Label>
                                    <Image Source="weather.png"></Image>
                                    <Label Text="{Binding wheather_type }"></Label>
                                    <Image Source="volume.png"  ></Image>
                                    <Label Text="{Binding noise}"></Label>
                                    <Label Text="dB"></Label>
                                </StackLayout>


                                <StackLayout Orientation="Horizontal">
                                    <Image></Image>
                                    <Label Text="{Binding rated_count }"></Label>
                                </StackLayout>

                                <StackLayout Orientation="Horizontal">
                                    <Label Text="Price: " VerticalOptions="Center"></Label>
                                    <Label Text="{Binding price }" VerticalOptions="Center" TextColor="Green"></Label>
                                    <Label Text=" EUR" VerticalOptions="Center"></Label>

                                </StackLayout>
                                <StackLayout Orientation="Horizontal">
                                    <StackLayout.GestureRecognizers>
                                        <TapGestureRecognizer Tapped="TapGestureRecognizer_Tapped_1" >

                                        </TapGestureRecognizer>
                                    </StackLayout.GestureRecognizers>
                                    <StackLayout BackgroundColor="Red" Orientation="Horizontal" Margin="5" >
                                        <Image Source="shoppingcart.png" Margin="10,0,0,0"></Image>
                                        <Label Text="Add to Cart" VerticalOptions="Center" HorizontalOptions="EndAndExpand" Margin="0,0,10,0" ></Label>
                                    </StackLayout>
                                    <Image x:Name="button_info"  Source="info.png" >

                                        <Image.GestureRecognizers>
                                            <TapGestureRecognizer Tapped="button_info_Clicked"></TapGestureRecognizer>
                                        </Image.GestureRecognizers>

                                    </Image>
                                </StackLayout>

                            </StackLayout>

                        </Grid>
                    </StackLayout>

                </ViewCell>

            </DataTemplate>

        </ListView.ItemTemplate>

        <ListView.Footer>
            <Grid Padding="6" IsVisible="{Binding IsBusy}">
                <!-- set the footer to have a zero height when invisible -->
                <Grid.Triggers>
                    <Trigger TargetType="Grid" Property="IsVisible" Value="False">
                        <Setter Property="HeightRequest" Value="0" />
                    </Trigger>
                </Grid.Triggers>
                <!-- the loading content -->
                <Label Text="Loading..." TextColor="DeepPink" FontSize="20" FontAttributes="Bold" VerticalOptions="Center" HorizontalOptions="Center" />
            </Grid>
        </ListView.Footer>
    </ListView>
    <Button Clicked="button_Change_Order_Clicked"></Button>
</StackLayout>

    


    


     public class MainViewModel : INotifyPropertyChanged
{
    private bool _isBusy;
    private const int PageSize = 10;
    readonly DataService _dataService = new DataService();

    public InfiniteScrollCollection<Product_Search> Items { get; }

    public bool IsBusy
    {
        get => _isBusy;
        set
        {
            _isBusy = value;
            OnPropertyChanged();
        }
    }
    public MainViewModel()
    {
        Items = new InfiniteScrollCollection<Product_Search>
        {
            OnLoadMore = async () =>
            {
                IsBusy = true;

                // load the next page
                var page = Items.Count / PageSize;
                var items = await _dataService.GetItemsAsync(page, PageSize);

                IsBusy = false;

                // return the items that need to be added
                return items;
            },
            OnCanLoadMore = () =>
            {
                return Items.Count < 44;
            }
        };

        DownloadDataAsync();
    }

    private async Task DownloadDataAsync()
    {
        var items = await _dataService.GetItemsAsync(pageIndex: 0, pageSize: PageSize);
        Items.AddRange(items);
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

    


    }
    


    任何帮助都是非常重要的。
    1 回复  |  直到 6 年前
        1
  •  1
  •   polkduran    6 年前

    你的 ListView.Items 属性已绑定到 MainViewModel.Items 属性A PropertyChanged event 需要触发以指示属性值的更改(与属性本身或其内容相对应,如果 InfiniteScrollCollection<> 是一个可观察的集合)。

    当你想替换 Items 来源你可以给它一个新的值,信号它已经改变,你的 ListView 可以刷新: 

    private InfiniteScrollCollection<Product_Search> _items;
public InfiniteScrollCollection<Product_Search> Items 
{ 
    get { return _items; }
    set
    {
        _items = value;
        OnPropertyChanged();
    }
}
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