[英]Mapping string bind-Value directly to an integer property in Blazor component
我正在開發自定義 blazor select 組件。 該組件有一個名為“Value”的屬性,在大多數情況下它是一個字符串值,我可以毫無問題地使用@bind-Value 綁定到它。
但是,在某些情況下,它綁定的屬性可能是 integer(在組件外部),在這種情況下,我需要將字符串轉換為 integer。我最初假設只需使用 Int32.Parse 即可完成此操作,如下所示:
Select.razor.cs
namespace Accounting.Web.Components
{
public partial class Select
{
[Parameter]
public string Value { get; set; } = default!;
[Parameter]
public EventCallback<string>? ValueChanged { get; set; }
public void OnClick()
{
Value = "2";
ValueChanged?.InvokeAsync(Value);
}
}
}
Index.razor.cs
<Select Id="InvestmentEntitySelect" @bind-Value="@Int32.Parse(AddDto.InvestmentEntityId)">
@foreach (var entity in Entities)
{
<SelectOption Value="@entity.InvestmentEntityId.ToString()">@entity.Name</SelectOption>
}
</Select>
AddDto.cs
namespace Accounting.Shared.Dtos.Request.Investment
{
public class AddDto
{
[Required]
public int? InvestmentEntityId { get; set; } = 0;
[Required]
public string Description { get; set; } = String.Empty;
}
}
感興趣的是:
@bind-Value="@Int32.Parse(AddDto.InvestmentEntityId)"
但不幸的是,這會產生一個錯誤:
參數 1:無法從“int”轉換為“System.ReadOnlySpan”
那么在上面的示例中,如何將綁定值轉換為 integer 呢?
你必須這樣做:
<Select Id="InvestmentEntitySelect" Value="@AddDto.InvestmentEntityId.ToString()" ValueChanged="OnValueChanged">
@foreach (var entity in Entities)
{
<SelectOption Value="@entity.InvestmentEntityId.ToString()">@entity.Name</SelectOption>
}
</Select>
@code {
private void OnValueChanged(string selectedValue)
{
AddDto.InvestmentEntityId = int.Parse(selectedValue);
}
}
您需要像下面這樣創建一個自定義輸入 select 並覆蓋它的TryParseValueFromString
方法:
public class CustomInputSelect<TValue> : InputSelect<TValue>
{
protected override bool TryParseValueFromString(
string? value,
out TValue result,
out string? validationErrorMessage)
{
if (typeof(TValue) == typeof(int))
{
if (int.TryParse(value, out var resultInt))
{
result = (TValue)(object)resultInt;
validationErrorMessage = null;
return true;
}
else
{
result = default;
validationErrorMessage =
$"The selected value {value} is not a valid number.";
return false;
}
}
else
{
return base.TryParseValueFromString(value, out result,
out validationErrorMessage);
}
}
}
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