NullReferenceException 未处理 C# [英] NullReferenceException was unhandled C#

问题描述

Visual Studio 2010 - C# 中的(Windows 窗体)

Visual Studio 2010 - (Windows Forms) in C#

我有这个代码:

private void cbxValuta_SelectedIndexChanged(object sender, EventArgs e)
    {
        try
        {
            string primo = cbxValuta.SelectedItem.ToString();
            string secondo = cbxValuta2.SelectedItem.ToString();
            double cambio = double.Parse(CurrencyConverter.Convert(1.0m, primo, secondo));
            tbxConvertito.Text = (double.Parse(tbxDaConvertire.Text) * cambio).ToString();

我收到此错误:

NullReferenceException 未处理未将对象引用设置为对象的实例.

NullReferenceException was unhandled Object reference not set to an instance of an object.

我该如何解决这个问题?

How Can I solve this issue?

推荐答案

SelectedItem 如果未在 UI 元素中选择任何项目，则返回 null.尝试添加检查项目是否已被选中

SelectedItem return null if no item was selected in a UI element. Try to add check if items has been selected

if(cbxValuta.SelectedItem != null && cbxValuta2.SelectedItem != null)
{
       string primo = cbxValuta.SelectedItem.ToString();
       string secondo = cbxValuta2.SelectedItem.ToString();
//       ....
}

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