ant-design-blazor/components/calendar/internal/CalendarHeader.razor

@namespace AntDesign
@inherits AntDomComponentBase
@using AntDesign.Internal

<div class="@(PrefixCls)-header"
     style="@Style"
     id="@Id"
     @ref="@Ref">
    @{
        int startYear = Calendar.Value.AddYears(-10).Year;
        int endYear = Calendar.Value.AddYears(10).Year;

        if (Calendar.ValidRange != null)
        {
            startYear = Calendar.ValidRange[0].Year;
            endYear = Calendar.ValidRange[1].Year;
        }

        string yearFormat = Calendar.Locale.Lang.YearFormat;
    }
    <Select Class=@($"{PrefixCls}-year-select")
            @bind-Value="@_yearValue"
            Size=@(Calendar.FullScreen ? AntSizeLDSType.Default : AntSizeLDSType.Small)
            DefaultValue=@Calendar.Value.Year
            TItemValue="int"
            TItem="string"
            Style="width: 70px;"
            SortByLabel="@SortDirection.Ascending"
            OnSelectedItemChanged="@(async (item) => await OnSelectYear(item))">
            <SelectOptions>
                @for (int year = startYear; year <= endYear; year++)
                {
                    DateTime yearDate = new DateTime(year, 1, 1);
                    <SelectOption @key="@yearDate.Year" TItemValue="int" TItem="string" Value=@yearDate.Year Label="@(yearDate.ToString(yearFormat, Calendar.CultureInfo))" />
                }
            </SelectOptions>        
    </Select>

    @if (Calendar.Mode == DatePickerType.Month)
    {
        int startMonth = 1;
        int endMonth = 12;

        if (Calendar.ValidRange != null)
        {
            startMonth = Calendar.Value.Year == Calendar.ValidRange[0].Year ? Calendar.ValidRange[0].Month : startMonth;
            endMonth = Calendar.Value.Year == Calendar.ValidRange[1].Year ? Calendar.ValidRange[1].Month : endMonth;
        }

        string monthFormat = Calendar.Locale.Lang.MonthFormat;

        <Select class=@($"{PrefixCls}-month-select")
                @bind-Value="@_monthValue"
                Size=@(Calendar.FullScreen ? AntSizeLDSType.Default : AntSizeLDSType.Small)
                DefaultValue=@Calendar.Value.Month
                Style="width: 70px;"
                TItemValue="int"
                TItem="string"
                OnSelectedItemChanged="@(async (item) => await OnSelectMonth(item))">
                <SelectOptions>
                    @for (int month = startMonth; month <= endMonth; month++)
                    {
                        DateTime monthDate = new DateTime(1, month, 1);
                        <SelectOption @key="@monthDate.Month" TItemValue="int" TItem="string" Value=@monthDate.Month Label="@(monthDate.ToString(monthFormat, Calendar.CultureInfo))" />
                    }
                </SelectOptions>            
        </Select>
    }

    <RadioGroup class=@($"{PrefixCls}-mode-switch")
                Size=@(Calendar.FullScreen ? AntSizeLDSType.Default : AntSizeLDSType.Small)
                Value="@Calendar.Mode"
                OnChange="OnModeChange" TValue="string">
        <Radio RadioButton Value="@DatePickerType.Month">@(Calendar.Locale.Lang.Month)</Radio>
        <Radio RadioButton Value="@DatePickerType.Year">@(Calendar.Locale.Lang.Year)</Radio>
    </RadioGroup>
</div>

@code
{
    [CascadingParameter(Name = "PrefixCls")]
    public string PrefixCls { get; set; }

    [CascadingParameter(Name = "Calendar")]
    public Calendar Calendar { get; set; }

    private DateTime currentDate;
    private int _yearValue;
    private int _monthValue;

    protected override void OnInitialized()
    {
        base.OnInitialized();

        currentDate = Calendar.Value;
    }

    private void OnModeChange(string value)
    {
        Calendar.ChangePickerType(value);
    }

    private async Task OnSelectYear(string value)
    {      
        int year = Convert.ToInt32(value);
        await Calendar.ChangeValue(DateHelper.CombineNewDate(Calendar.Value, year: year));
    }

    private async Task OnSelectMonth(string value)
    {
        int month = Convert.ToInt32(value);
        await Calendar.ChangeValue(DateHelper.CombineNewDate(Calendar.Value, month: month));
    }
}