如何创建dybanic标签并使用asp.net c＃通过数据库插入数据 [英] how to create dybanic label and insert data through database using asp.net c#

问题描述

嗨......这是我的代码

hi... here is my code

d=25;
Label[] lb1 = new Label[d];
string strd = "select monthly from feehead where fee_head='" + lb.Text + "'";
da = new SqlDataAdapter(strd, con);
DataSet ds11 = new DataSet();
da.Fill(ds11);
for (int l = 1; l < d; l++)
 {
     lb1[l].Text = ds11.Tables[0].Rows[0][0].ToString();
}

数据库是：

database is:

CREATE TABLE [FEEHEAD] (
    [ACT_CODE] [int] NULL ,
    [FEE_HEAD] [nvarchar] (25) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
    [MONTHLY] [bit] NOT NULL ,
    [CL_BASED] [bit] NOT NULL ,
    [AMOUNT] [float] NULL ,
    [SHNAME] [nvarchar] (50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
    [EMP] [float] NULL ,
    [CCL] [float] NULL ,
    [SPL] [float] NULL ,
    [EXT] [float] NULL ,
    [AccG] [int] NULL ,
    [HType] [nvarchar] (50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
    [APR] [bit] NOT NULL ,
    [may] [bit] NOT NULL ,
    [JUN] [bit] NOT NULL ,
    [JUL] [bit] NOT NULL ,
    [AUG] [bit] NOT NULL ,
    [SEP] [bit] NOT NULL ,
    [OCT] [bit] NOT NULL ,
    [NOV] [bit] NOT NULL ,
    [DECM] [bit] NOT NULL ,
    [JAN] [bit] NOT NULL ,
    [FEB] [bit] NOT NULL ,
    [MAR] [bit] NOT NULL
) ON [PRIMARY]
GO

我的错误是：

对象引用未设置为对象的实例。

and my error is:
Object reference not set to an instance of an object.

推荐答案

Member 11865955写道：

Member 11865955 wrote:

Label[] lb1 = new Label[d];
...
for (int l = 1; l < d; l++)
{
     lb1[l].Text = ds11.Tables[0].Rows[0][0].ToString();
}

你创建了一个数组，它可以容纳一定数量的标签对象。创建数组时，所有元素都设置为数组类型的默认值，在本例中为 null 。



然后尝试在数组中的每个元素上设置属性。但是你没有改变任何元素的默认值，所以你试图在 null 引用上设置一个属性。



你需要在循环中创建一个新的 Label 实例，设置它的 Text 属性，然后将其存储在数组中：

You've created an array which can hold a certain number of Label objects. When you create an array, all of the elements are set to the default value for the array type, which in this case is null.

You then attempt to set a property on each element in the array. But you haven't changed the default value of any of the elements, so you're trying to set a property on a null reference.

You need to create a new Label instance within the loop, set its Text property, and then store it in the array:

for (int l = 1; l < d; l++)
{
    Label label = new Label();
    label.Text = ds11.Tables[0].Rows[0][0].ToString();
    lb1[l] = label;
}

您可以通过使用调试器逐步执行代码来轻松识别此问题。

You could have easily identified this problem yourself by using the debugger to step through your code.

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