Xamarin 形式：System.InvalidCastException：'指定的转换无效

Posted 2023-04-13

【中文标题】Xamarin 形式：System.InvalidCastException：\'指定的转换无效

【英文标题】：Xamarin forms: System.InvalidCastException: 'Specified cast is not validXamarin 形式：System.InvalidCastException：'指定的转换无效

【发布时间】：2021-08-03 06:33:40

【问题描述】：

我在 xamarin 中有一个列表视图，当我尝试在按钮单击事件中投射所选项目时，它给了我错误。 SavedVira 类用于 sqlite 数据库表，我正在尝试使用异步，但它似乎更麻烦然后值得。 （我对编程很陌生）。这是我的代码：

XAML：

<ListView x:Name="SavedViraView" HasUnevenRows="True" ItemTapped="SavedViraView_ItemTapped">
        <ListView.ItemTemplate>
            <DataTemplate>
                <ViewCell>
                    <ViewCell.View>
                        <StackLayout Padding="10">
                            <Label Text="Navn:" FontSize="18" FontAttributes="Bold"/>
                            <Label Text="Binding Virusnavn" FontSize="15"/>
                            <Label Text="Symptomer:" FontSize="18" FontAttributes="Bold"/>
                            <Label Text="Binding symptom1"/>
                            <Label Text="Binding symptom2"/>
                            <Label Text="Binding symptom3"/>
                            <Label Text="Binding symptom4"/>
                            <Label Text="Binding symptom5"/>
                            <Label Text="Binding symptom6"/>
                            <Label Text="Lavet af:" FontSize="18" FontAttributes="Bold"/>
                            <Label Text="Binding Creator"/>
                            <Button Text="Load" x:Name="LoadButton" Clicked="LoadButton_Clicked"/>
                        </StackLayout>
                    </ViewCell.View>
                </ViewCell>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>

XAML.CS：

private ObservableCollection<SavedVira> SavedVira = new ObservableCollection<SavedVira>();
    public Åben()
    
        InitializeComponent();
    

    protected override void OnAppearing()
    
        nameLabel.Text = Values.currentUser;
        Init();
    

    private async void Init()
    
        BindingContext = new SavedVira();
        var Viralist = await DataServices.GetSavedVira();
        SavedVira = new ObservableCollection<SavedVira>(Viralist);
        SavedViraView.ItemsSource = SavedVira;
    


    private void LoadButton_Clicked(object sender, EventArgs e)
    
        var LoadVirus = ((ListView)sender).SelectedItem as SavedVira;
        if (LoadVirus == null)
            return;
        Values.LoadBool = true;
        Values.symptomZero = LoadVirus.symptom1;
        Values.symptomOne = LoadVirus.symptom2;
        Values.symptomTwo = LoadVirus.symptom3;
        Values.symptomThree = LoadVirus.symptom4;
        Values.symptomFour = LoadVirus.symptom5;
        Values.symptomFive = LoadVirus.symptom6;

    

SavedVira 演员/模特：

[Table("savedvira")]
public class SavedVira

    [PrimaryKey, AutoIncrement]
    [Column("id")]
    public int Id  get; set; 

    [Column("virusnavn")]
    public string Virusnavn  get; set; 

    [Column("creator")]
    public string Creator  get; set; 

    [Column("symptoms1")]
    public string symptom1  get; set; 

    [Column("symptoms2")]
    public string symptom2  get; set; 

    [Column("symptoms3")]
    public string symptom3  get; set; 

    [Column("symptoms4")]
    public string symptom4  get; set; 

    [Column("symptoms5")]
    public string symptom5  get; set; 

    [Column("symptoms6")]
    public string symptom6  get; set; 

任何帮助将不胜感激！

【参考方案1】：

sender 是 Button，所以这不起作用

var LoadVirus = ((ListView)sender).SelectedItem as SavedVira;

改为这样做

var btn = (Button)sender;
var selected = (SavedVira)btn.BindingContext;

另外，对实例变量和类使用相同的名称会造成混淆，我建议您避免使用它

SavedVira = new ObservableCollection<SavedVira>(Viralist);