App Config configuration file error

Preface

Beginners do upper computer development , In the process of connecting to the database , If you use The configuration file App.config To get the connection string , There are likely to be some problems , Let's summarize these problems today , And give solutions .

error message 1

“ The object reference is not set to an instance of the object ”.

《C# Program 》 Error prompt for ：

【 Problem analysis 】： open App.config file , Check name Whether the string in the node is the same as that in the current brackets , Compared with , Dissimilarity , One more. S, please remember ,C# Read the name in brackets used by the node , And configuration file node configuration name It has to be consistent ！

Solution

【 Problem solving 】 hold s Get rid of , Can run .

【 Other situations 】1： Some friends don't pay attention , In the string , Add any space , It can also lead to this problem , For example, below ：

The blank space must be removed , In the configuration file , You can't just add any spaces .

【 Other situations 】2： If you write the node position wrong, the above error will also appear , For example, the screenshot below , The node should be written to the arrow position .

【 Other situations 】3： If App.config Configuration file not added , perhaps App.config The file didn't go to , The project can be started under the project directory , There will also be the above mistakes . For example, the following is wrong ：

The following green part is the startable item of the project ,App.config The file must be put here .

【 Other situations 】4： Changed the name of the configuration file , Configuration file requirements must be default App.config Talent , If you change the file name , There are also mistakes , For example, the following is not allowed ：

error message 2

“ThreeLayer.DAL.SQLHelper” The type initializer for threw an exception .

《C# Program 》 Error prompt for ：

【 Problem analysis 】 Just a hint “SQLHelper The type initializer of threw an exception ”. It's usually a configuration file problem , Because we use App.config The configuration file saves the data connection string . For beginners , Because I can't understand this mistake , So I don't know where to start , Here, please remember the following troubleshooting methods .

Solution

【 resolvent 1】 The configuration file node is incorrectly written ：

Originally, the node name of this place is, that is, one is missing from the above s, Change to the following ：

【 resolvent 2】 The configuration file App.config If the file name is changed 、 Didn't put it in “ Can start the project ” root directory , yes , we have VS The above error will also appear in the version .（ This and error 1 The solution is the same ）

summary

According to the above method, we can solve the problem perfectly App.config Frequently asked questions about how to get the connection string . I hope today's content can help you .