你调用的对象是空的. -App.config [英] Object reference not set to an instance of an object. - App.config

问题描述

我收到错误，并且在本地窗口中看到conSettings和connectionString值均为null.我正确地说ConfigurationManager为null，我需要创建一个新对象.也许我正在使用Access，也许我错过了App.config文件中的某些内容.请有人能帮助我解决这个问题.预先感谢.

I receiving the error and in the local window I am seeing for both conSettings and connectionString value of null. I am right to say ConfigurationManager is null and I need to create a new object. Maybe I am using Access and perhaps I have missed something in App.config file. Can someone help me on how to solve this problem, please. Thanks in advance.

App.config文件...

App.config file...

   <?xml version="1.0" encoding="utf-8" ?>
    <configuration>
    <appSettings>
       <add key="MyDBConnectionString" value="Provider=Microsoft.Jet.OLEDB.4.0;Data 
                   Source=E:\...\Database1.mdb"/>
    </appSettings>
    </configuration>

Form.cs文件...

Form.cs file...

 private void btnShow_Click(object sender, EventArgs e)
    {
        ConnectionStringSettings conSettings = ConfigurationManager.ConnectionStrings["MyDBConnectionString"];

        string connectionString = ConfigurationManager.ConnectionStrings["MyDBConnectionString"].ConnectionString; // error points here

        try
        {
            con = new OleDbConnection(connectionString);
            con.Open();
            cmd = new OleDbCommand("SELECT * FROM Table1", con);
            objReader = cmd.ExecuteReader();
            while (objReader.Read())
            {
                txtID.Text = ds.Tables[0].Rows[rno][0].ToString();
                CBAgeGroup.Text = ds.Tables[0].Rows[rno][1].ToString();
                CBGender.Text = ds.Tables[0].Rows[rno][2].ToString();
                CBCrimOffen.Text = ds.Tables[0].Rows[rno][3].ToString();
                if (ds.Tables[0].Rows[rno][4] != System.DBNull.Value)
                {
                    photo_aray = (byte[])ds.Tables[0].Rows[rno][4];
                    MemoryStream ms = new MemoryStream(photo_aray);
                   pictureBox1.Image = Image.FromStream(ms);
                }
                txtCV.Text = ds.Tables[0].Rows[rno][5].ToString();
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
        finally
        {
            con.Close();
        }
    }

已建议我使用App.config.

I have been advised to use App.config.

VS 2010 C# MS Access 2003

VS 2010 C# MS Access 2003

更新1 我的App.config现在看起来像这样...

UPDATE 1 My App.config now looks like this...

<configuration>
    <ConnectionString>
        <add key="MyDBConnectionString"   value="Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Raj\Education\C_Sharp\Test1\Database1.mdb"/>
    </ConnectionString>

我现在收到以下错误:配置系统初始化失败".我现在正在Google上查看它.

I am now receiving error of..."Configuration system failed to initialize". I am looking at it now on Google.

更新2 尝试过...

<configuration>
 <connectionStrings>
<add name="MyDBConnectionString" connectionString="Provider=Microsoft.Jet.OLEDB.4.0;Data   
        Source=E:\...\Database1.mdb"/>
  </connectionStrings>
 </configuration>

再次收到谷歌搜索对象引用未设置为对象实例的错误"

Receiving error of "Object reference not set to an instance of an object" Googling again

更新3

<configuration>
<connectionStrings>
    <clear />
    <add name="MyDBConnectionString"
     providerName="System.Data.OleDb" connectionString="Provider=Microsoft.Jet.OLEDB.4.0; Source=\Database1.mdb" />
</connectionStrings>

在更新3中，我收到相同的错误.我已经包括了添加参考系统.配置，我已经使用System.Configuration进行了引用；

With the update 3 I am receiving error the same error. I have included the Add reference System. Configuration and I have referenced using System.Configuration;

结论

也许VS 2010和Access 2003之间可能存在技术问题.这次我将不使用App.config.我知道SQL Server不会有问题.因此，我将保留该内容.感谢Damith和Clint的宝贵时间.

Perhaps it maybe there is a technical gitch between VS 2010 and Access 2003. I shall not use App.config this time round. I know there will be no problem with SQL Server. So I will leave it that. Thanks Damith and Clint for your time.

推荐答案

您需要阅读以下AppSettings键，

you need to read AppSettings key as below ,

string connectionString = 
      ConfigurationSettings.AppSettings["MyDBConnectionString"];

您仍然收到空值，请尝试以下步骤

still you receive empty value, try below steps

1. 在解决方案资源管理器中选择App.Config文件
2. 在属性窗口中，选择复制到输出目录以进行复制" 总是.
3. 现在，构建应用程序，然后重试.

1. Select the App.Config file in the solution explorer
2. In the property window select Copy to Output Directory to Copy Always.
3. Now Build the application and try again.

要像下面那样访问，您需要在应用程序配置中添加connectionStrings部分

to access like below you need to add connectionStrings section in app config

  string connectionString = 
      ConfigurationManager.ConnectionStrings["MyDBConnectionString"].ConnectionString; // error points here

示例应用配置

<?xml version="1.0"?>
<configuration>
  <connectionStrings>
    <add name="MyDBConnectionString" 
    connectionString="Provider=Microsoft.Jet.OLEDB.4.0;Data 
               Source=E:\...\Database1.mdb"/>
  </connectionStrings>
</configuration>

这篇关于你调用的对象是空的. -App.config的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！