循环遍历数据表以获取值 [英] Looping through data table to get value

问题描述

我有一个包含多行的数据表.我正在使用 foreach 循环来遍历每个项目并返回名称.这将为每一行返回相同的(第一个)值.我做错了什么?

I have a DataTable with multiple rows. I'm using a foreach loop to loop through each item and return the name. This is returning the same (1st) value for each row. What have I done wrong?

            DataTable table = new DataTable();
            table.Columns.Add("tag", typeof(string));
            string name = hfSelected.Value;
            string[] names = name.Split(',');
            for (int i = 0; i < names.Length; i++)
                table.Rows.Add(new object[] { names[i] });                  
            DataRow row = table.Rows[0];

            foreach (var item in table.Rows)
            {

                Value = row["tag"].ToString() // this is returning the same value for both items in the table.

            }

推荐答案

在您提到您收到错误的评论中:

In a comment you mentioned that you get the error:

不能将带有 [] 的索引应用于对象类型的表达式

cannot apply indexing with [] to an expression of type object

在 foreach 循环中尝试访问 item["tag"] 时.

when trying to access item["tag"] in the foreach loop.

您需要在 foreach 中显式声明 DataRow.

You need to explicitly declare the DataRow in the foreach.

// declare DataRow here, not var 
foreach (DataRow item in table.Rows)
{
    // use item here
    Value = item["tag"].ToString();    // use += to concatenate string
}

原因是 DataRowCollection 实现了一个非通用的 IEnumerable 所以你索引一个 object 而不是 DataRow.上面的解决方案转换为 DataRow.

The reason is that the DataRowCollection implements a non-generic IEnumerable so you index an object instead of DataRow. The solution above casts to a DataRow.

我建议查看 System.Data.DataSetExtensions 中的 Field() 和 AsEnumerable() 方法.AsEnumerable() 返回 IEnumerable.Field() 提供对值的强类型访问(即它为您强制转换/转换类型).

I would recommend looking at the Field<T>() and AsEnumerable() methods from System.Data.DataSetExtensions. AsEnumerable() returns an IEnumerable<DataRow>. Field() provides strongly typed access to the values (ie it casts/converts the types for you).

然后你可以这样做:

foreach (var item in table.AsEnumerable())
{
    // item is a DataRow here
    var myString = item.Field<string>("tag");     // gets string

    // you can also do
    var myInt = item.Field<int>("Id");            // gets int
    var myDate = item.Field<DateTime?>("Date");   // gets nullable DateTime?
    var myValue = item.Field<decimal>("Price");   // gets decimal
}

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