如果更改组合框值，则更改文本框值 (System.FormatException: 'Input string was not in a correct format.')

Question

如果我更改组合框索引，我将尝试自动加载文本框值但不明白如果我加载我的表单我收到这个错误？

我处理我的 null，如果我忽略这一行，一切都很好！

这是我的表格

这是我的存储库

区域资源库

public string GetAreaNamebyAreaID(int areaID)
{
    var result = db.btbArea.SingleOrDefault(g => g.AreaID == areaID);

    if (result == null)
        return string.Empty;

    return result.AreaName;
}

HowzehRepository

public string GetHowzehNamebyHoezehID(int howzehID)
{
    var result = db.btbHowzeh.SingleOrDefault(g => g.HowzehID == howzehID);
    if (result == null)
        return string.Empty;

    return result.HowzehName;
}

Paygah存储库

public string GetPaygahNamebyPaygahID(int paygahID)
{
    var result = db.btbPaygah.SingleOrDefault(g => g.PaygahID == paygahID);
    if (result == null)
        return string.Empty;

    return result.PaygahName;
}

如果我更改我的组合框索引，我将尝试加载我的文本框值

private void frmAreasManage_Load(object sender, EventArgs e)
{
    //Load AreaComboBox Source from AreaTable
    using (UnitOfWork db = new UnitOfWork())
    { 
        cmbAreaNumber.DataSource = db.AreaRepository.Get();
        cmbAreaNumber.DisplayMember = "AreaNumber";
        cmbAreaNumber.ValueMember = "AreaID";
    }
}

private void cmbAreaNumber_SelectedIndexChanged(object sender, EventArgs e)
{
    string selectedValue = cmbAreaNumber.SelectedValue.ToString();
    using (UnitOfWork db = new UnitOfWork())
        if (!string.IsNullOrEmpty(selectedValue))
        {
            {
                //Load HowzehhComboBox From HowzehTable Filter By AreaID
                cmbHowzehNumber.DataSource = db.HowzehRepository.GetNameIDByFilter(selectedValue);

                cmbHowzehNumber.DisplayMember = "HowzehNumber";
                cmbHowzehNumber.ValueMember = "HowzehID";

                //Get AreaName from AreaTable Filter By AreaID
                txtAreaName.Text = db.AreaRepository.GetAreaNamebyAreaID(Convert.ToInt32(selectedValue));
            }
        }
}

private void cmbHowzehNumber_SelectedIndexChanged(object sender, EventArgs e)
{
    string selectedValue = cmbHowzehNumber.SelectedValue.ToString();
    using (UnitOfWork db = new UnitOfWork())
        if (!string.IsNullOrEmpty(selectedValue))
        {
            //Load PaygahComboBox From PaygahTable Filter By HowzehID
            cmbPaygahNumber.DataSource = db.PaygahRepository.GetNameIDByFilter(selectedValue);

            cmbPaygahNumber.DisplayMember = "PaygahNumber";
            cmbPaygahNumber.ValueMember = "PaygahID";
            //Get HowzehName from HowzehTable Filter By HowzehID
            txtHowzehName.Text = db.HowzehRepository.GetHowzehNamebyHoezehID(Convert.ToInt32(selectedValue));
        }
}

private void cmbPaygahNumber_SelectedIndexChanged(object sender, EventArgs e)
{
    using (UnitOfWork db = new UnitOfWork())
    {
        //Get HowzehName from HowzehTable Filter By HowzehID
        txtPaygahName.Text = db.PaygahRepository.GetPaygahNamebyPaygahID(Convert.ToInt32(selectedValue));
    }
}

Answer 1

TL;DR

要解决您的问题，请对方法进行下一步更改 frmAreasManage_Load：

private void frmAreasManage_Load(object sender, EventArgs e)
{
    //Load AreaComboBox Source from AreaTable
    using (UnitOfWork db = new UnitOfWork())
    { 
        // At first assign properties DisplayMember and ValueMember.
        cmbAreaNumber.DisplayMember = "AreaNumber";
        cmbAreaNumber.ValueMember = "AreaID";

        // And then assign DataSource property of the cmbAreaNumber.
        cmbAreaNumber.DataSource = db.AreaRepository.Get();
    }
}

说明

为什么要在DataSource之前赋值ValueMember 属性?

当我们分配 DataSource 属性时，分配集合的第一项变为 ComboBox 的 SelectedValue。这会触发 ComboBox.SelectedIndexChanged 事件。

如果我们在 ValueMember 之前分配 DataSource（因此 ValueMember = null），那么 CombobBox.SelectedValue 就是集合本身的第一项。在你的例子中 SelectedValue 是一个 btbArea 类型的对象。因此，当我要求您使用 cmbAreaNumber_SelectedIndexChanged 处理程序中的下一个代码时

txtAreaName.Text = db.AreaRepository.GetAreaNamebyAreaID(((btbArea) cmbAreaNumber.SelectedValue).AreaID);

它解决了第一次加载的问题。但是后来你得到了System.InvalidCastException: 'Unable to cast object of type 'System.Int32' to type 'Gim.DataLayer.btbArea'。发生此错误是因为 ValueMember 属性被分配给值 AreaID 并且从那一刻起 ComboBox.SelectedValue 是属性 int AreaID 的值btbArea.

如果我们分配 ValueMember = "AreaID"，然后分配 DataSource，那么每当引发 ComboBox.SelectedIndexChanged 事件时，SelectedValue 就是属性 [=28= 的值].因此，为了防止 SelectedValue 成为 btbArea 类型的对象（当 ValueMember = null 时的情况），我们必须首先分配 ValueMember 然后 DataSource.

如果更改组合框值，则更改文本框值 (System.FormatException: 'Input string was not in a correct format.')

Change textbox value if change combobox value (System.FormatException: 'Input string was not in a correct format.')

c#

combobox

winforms

TL;DR

说明