如何检查appSettings键是否存在？

Question

如何检查应用程序设置是否可用？

即app.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key ="someKey" value="someValue"/>
  </appSettings>
</configuration>

并在代码文件中

if (ConfigurationManager.AppSettings.ContainsKey("someKey"))
{
  // Do Something
}else{
  // Do Something Else
}

Answer 1

MSDN:Configuration Manager.AppSettings

if (ConfigurationManager.AppSettings[name] != null)
{
// Now do your magic..
}

要么

string s = ConfigurationManager.AppSettings["myKey"];
if (!String.IsNullOrEmpty(s))
{
    // Key exists
}
else
{
    // Key doesn't exist
}

Answer 2

if (ConfigurationManager.AppSettings.AllKeys.Contains("myKey"))
{
    // Key exists
}
else
{
    // Key doesn't exist
}

Answer 3

通过泛型和LINQ安全返回默认值.

public T ReadAppSetting<T>(string searchKey, T defaultValue, StringComparison compare = StringComparison.Ordinal)
{
    if (ConfigurationManager.AppSettings.AllKeys.Any(key => string.Compare(key, searchKey, compare) == 0)) {
        try
        { // see if it can be converted.
            var converter = TypeDescriptor.GetConverter(typeof(T));
            if (converter != null) defaultValue = (T)converter.ConvertFromString(ConfigurationManager.AppSettings.GetValues(searchKey).First());
        }
        catch { } // nothing to do just return the defaultValue
    }
    return defaultValue;
}

使用如下:

string LogFileName = ReadAppSetting("LogFile","LogFile");
double DefaultWidth = ReadAppSetting("Width",1280.0);
double DefaultHeight = ReadAppSetting("Height",1024.0);
Color DefaultColor = ReadAppSetting("Color",Colors.Black);