数据绑定并不构成负荷工作之前 - 只有在窗体加载初始化组合框项目 [英] Databinding doesn't work before Form Load - ComboBox Items initialized only after Form load

问题描述

我有一个winform 2组合框，一个人从名单MYLIST其他的我想有从第一的选定索引的所有值，以后所有的值。但我认为这是将项目加载到组合框的一个问题。

I have two ComboBoxes on a winform, one has all the values from a List "MyList" the other I want to have all the values from the selected index of the first, onwards. But I think there is a problem with when items are loaded into the ComboBoxes.

public partial class Form1 : Form
{
    public Form1()
    {
        ComboBox box = new ComboBox();
        box.DropDownStyle = ComboBoxStyle.DropDownList;
        box.DataSource = MyList.ToList();
        box.SelectedIndexChanged += new EventHandler(ComboBox_SelectedIndexChanged);
        Tab_Page.Controls.Add(box);

        ComboBox box2 = new ComboBox();
        box2.DropDownStyle = ComboBoxStyle.DropDownList;
        foreach (object o in box.Items)
            {
                box2.Items.Add(o);
            }
        Tab_Page.Controls.Add(box2);
        box2.Items.RemoveAt(0);
        //This last line throws an error
        //"InvalidArgument=Value of '0' is not valid for 'index'."
    }}

这个错误是因为BOX2有其收藏中没有的项目，即使箱有从这个错误被抛出的瞬间列出所有的值。

The error is because box2 has no items in its collection, even though box has all the values from the List at the moment this error is thrown.

所以我不知道如何/时，到底是加载到项目集合项目，如何解决？本

So I was wondering how/when exactly are items loaded to the Items collection and how can I fix this?

推荐答案

数据绑定的形式和控制在 创建 状态和之前的窗体和控件获得可见他们不是在创建状态。

Data-binding will not work before the form and control be in Created status and before the form and controls get visible they are not in Created status.

问题此处是因为这样的事实。您正在使用数据绑定添加在构造项目第一个组合，并且如上所述，首先将数据绑定不会在环路有等工作，项目集合。组合是空的，没有的项目将加入到第二个组合

The problem here is because of above fact. You are using data-binding to add items to first combo in constructor and as mentioned above, the data-binding will not work there and so in the loop, Items collection of first combo is empty yet and no items will be added to second combo.

您可以使用这些选项解决问题：

You can solve the problem using either of these options:

• 直接添加值项目第一个组合的： box.Items.AddRange（MyList.ToArray（ ））;


• 把代码在所示或加载形式的事件。


• 请尝试检索第一个组合的项目前的形式显示。例如呼叫 this.Show（）; 到数据源第一个组合的赋值后。调用 this.Show（）; 或 THIS.VISIBLE = TRUE; 引起的形式和其所有可见的控制得到创建。所以控制应该是可见的，并应以可见形式的可见部分中的一员。

• Add values directly to Items of first combo: box.Items.AddRange(MyList.ToArray());
• Put the codes in Shown or Load event of the form.
• Make the form visible before trying to retrieve Items of first combo. For example call this.Show(); after assigning values to DataSource of first combo. Calling this.Show(); or this.Visible = true; causes the form and all of its visible controls get Created. So the controls should be visible and should be a member of visible part of a visible form.

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