- สร้างโดยคลิกขวาที่โปรเจค Add => New Item => Application Configuration File
- ถ้าโปรแกรมเราชื่อ console.exe เมื่อทำการ compile แบบ debug ไฟล์คอนฟิกที่เราทำการเพิ่มเข้าไปจะเป็น console.exe.config ซึ่งจะอยู่ใน bin/debug/ แล้วแต่ประเภทการคอมไพล์
- เมื่อเราคอมไฟล์โปรเจค ไฟล์ console.exe.config จะเปลี่ยนตามค่าใน app.config จำไว้ด้วย
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<appSettings>
<add key="p1" value="value1" />
<add key="p2" value="value2" />
</appSettings>
</configuration>
Reading
foreach(string key in ConfigurationManager.AppSettings)
{
string value = ConfigurationManager.AppSettings[key];
Console.WriteLine("Key: {0}, Value: {1}", key, value);
}
// string value = ConfigurationManager.AppSettings["p1"];
Writing
// Open App.Config of executable
System.Configuration.Configuration config =
ConfigurationManager.OpenExeConfiguration
(ConfigurationUserLevel.None);
// Add an Application Setting.
// if key exist it will append value
config.AppSettings.Settings.Add("p3","value3");
// Update value key must exist in config file
// if key not exist it will error or exception
config.AppSettings.Settings["p2"].Value = "Jui555";
// Remove key and value
config.AppSettings.Settings.Remove("p1");
// Save the changes in App.config file.
config.Save(ConfigurationSaveMode.Modified);
// Force a reload of a changed section.
ConfigurationManager.RefreshSection("appSettings");
Note:
# ถ้าขึ้น exception แบบนี้ น่าจะประมาณว่าไม่มี tag <appSettings></appSettings>
# เพราะว่าเมื่อเราทำการสร้าง app.config ขึ้นมาใหม่นั้นจะมีข้อมูลแค่เนี๋ย
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
</configuration>
# อีกอย่างอย่าลืม add reference และ resolve ได้เลย
- ส่วนทางด้านเว็บจะมี web.config ซึ่งเราสามารถเพิ่มค่าคอนฟิก แบบ application ได้ เหมือนกับ application ไม่มีผิดเพี้ยนเลย เพียงแต่ ConfigurationManager.AppSettings["key"]; จะไปอ่านค่าที่ web.config แทนที่จะเป็น app.config เหมือน application ซึ่งการเพิ่ม key ก็ยังทำเหมือน application app.config
<configuration>
<appSettings>
<add key="p1" value="value1" />
<add key="p2" value="value2" />
</appSettings>
</configuration>
ASP.NET provides a configuration system we can use to keep our applications flexible at runtime. In this article we will examine some tips and best practices for using the configuration system for the best results.
The
As an example, let’s examine this minimal web.config with an appSetting entry to hold our connection string:
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To read the key we use the ConfigurationSettings class from the System.Configuration namespace, as shown below.
12 private void Page_Load(object sender, EventArgs e)
13 {
14 string connectionInfo = ConfigurationSettings.AppSettings["ConnectionInfo"];
15 using(SqlConnection connection = new SqlConnection(connectionInfo))
16 {
17 connection.Open();
18
19 // perform work with connection
20
21 }
22 }
Some applications will duplicate these lines of code in many places. If we think about how the above code will evolve over time, we might see a handful of weaknesses. First, we have a hard coded string in place to fetch connection information from the web.config. Hard coded strings can be easy to mistype and difficult to track down if the key ever changes. Secondly, the code will tie us forever to the appSettings section of the web.config file. Although web.config is designed for just such a setting, we might find in the future that we need to pull configuration settings from a database, or change a setting from being application-wide to being a per-user configuration item kept in the Session or in a cookie.
Encapsulation
Let’s abstract away the source of the connection string using a class with a static property.
1 using System.Configuration;
2
3 namespace aspnet.config
4 {
5 public class Configuration
6 {
7 public static string ConnectionInfo
8 {
9 get
10 {
11 return ConfigurationSettings.AppSettings["ConnectionInfo"];
12 }
13
14 }
15 }
16 }
Now our Page_Load method looks like the following.
11 private void Page_Load(object sender, EventArgs e)
12 {
13 using(SqlConnection connection = new SqlConnection(Configuration.ConnectionInfo))
14 {
15 connection.Open();
16
17 // perform work with connection
18
19 }
20 }
The changes we made to the above code were relatively small - but powerful. Now the Page_Load function doesn’t know where the connection string comes from. We could easily change the ConnectionInfo property to retrieve the string from a different source without modifying any other code in the application. We also no longer have to remember the key string and hard code the string at various points in the application. Instead, we can utilize Visual Studio Intellisense when accessing the Configuration class to find the setting we need. The key value only appears once – inside the ConnectionInfo property – so we could again change the key name in the web.config and have only one line of code to update.
Of course this approach only works if all of the code in the application goes to the Configuration class instead of directly to web.config to retrieve settings. For each appSetting entry added to web.config we would add a corresponding property to the Configuration class.
Another advantage to this approach becomes apparent if we have an application setting that is not a string, but a date, integer, or other primitive type. In this case we could have the corresponding Configuration property parse the string from the web.config file and return the appropriate type.
You’ll notice we provided a read-only property for ConnectionInfo. The web.config file is not designed for constant updates. When an ASP.NET application launches a watch is put on the web.config file. ASP.NET will detect if the web.config changes while the application is running. When ASP.NET detects a change it will spin up a new version of the application with the new settings in effect. Any in process information, such as data kept in Session, Application, and Cache will be lost (assuming session state is InProc and not using a state server or database).
Next, let’s take a look at a little known feature of appSettings that can give us even more flexibility.
Multiple File Configuration
The appSettings element may contain a file attribute that points to an external file. Let’s change our web.config to look like the following.
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Next, we can create the external file ‘testlabsettings.config’ and add an appSettings section with our connection information.
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If the external file is present, ASP.NET will combine the appSettings values from web.config with those in the external file. If a key/value pair is present in both files, ASP.NET will use the value from the external file.
The feature demonstrated above is useful when you keep user-specific or environment-specific settings in the external file. Let web.config contain those settings that are global to all the installed instances of your application, while each user or installed site contains their own settings in an external file. This approach makes it easier to move around global web.config changes and keep web.config checked into source control, while each developer can get their own settings separate.
One caveat to this approach is that the ASP.NET runtime does not detect when the external file changes. You’ll need to make changes to web.config itself for ASP.NET to launch a new version of the application with all changes in effect.
I hope this article has given you some tips on using the appSettings section with the maximum amount of flexibility. To see the source code to additional best practices for configuration handling, download the Enterprise Library.
References
- http://www.codeproject.com/KB/cs/SystemConfiguration.aspx
- http://www.codeproject.com/KB/cs/Configuration_File.aspx
- http://www.ajaxline.com/node/258
- http://www.techtoolblog.com/archives/webconfig-connection-string-settings-in-net-20
- http://www.odetocode.com/Articles/345.aspx
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