Question

如何检查应用程序设置是否可用？

即。的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..
}

或

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);

Answer 4

如果您要查找的密钥不在配置文件中，您将无法将其转换为带有.ToString（）的字符串，因为该值将为null并且您将获得“对象”引用未设置为对象的实例“错误。在尝试获取字符串表示之前，最好首先查看该值是否存在。

if (!String.IsNullOrEmpty(ConfigurationManager.AppSettings["myKey"]))
{
    String myKey = ConfigurationManager.AppSettings["myKey"].ToString();
}

或者，正如Code Monkey建议：

if (ConfigurationSettings.AppSettings["myKey"] != null)
{
// Now do your magic..
}

Answer 5

如果您知道密钥类型尝试解析它们，则上层选项可以灵活应对所有方式 bool.TryParse(ConfigurationManager.AppSettings["myKey"], out myvariable);

Answer 6

我认为LINQ表达式可能是最好的：

   const string MyKey = "myKey"

   if (ConfigurationManager.AppSettings.AllKeys.Any(key => key == MyKey))
          {
              // Key exists
          }

Answer 7

var isAlaCarte = ConfigurationManager.AppSettings.AllKeys.Contains（＆＃34; IsALaCarte＆＃34;）＆amp;＆amp; bool.Parse（ConfigurationManager.AppSettings.Get（＆＃34; IsALaCarte＆＃34））;

Answer 8

我喜欢codebender's answer，但需要它才能在C ++ / CLI中工作。这就是我最后得到的。没有LINQ用法，但是可以。

generic <typename T> T MyClass::ReadAppSetting(String^ searchKey, T defaultValue) {
  for each (String^ setting in ConfigurationManager::AppSettings->AllKeys) {
    if (setting->Equals(searchKey)) { //  if the key is in the app.config
      try {                           // see if it can be converted
        auto converter = TypeDescriptor::GetConverter((Type^)(T::typeid)); 
        if (converter != nullptr) { return (T)converter->ConvertFromString(ConfigurationManager::AppSettings[searchKey]); }
      } catch (Exception^ ex) {} // nothing to do
    }
  }
  return defaultValue;
}

Answer 9

在TryParse中使用新的c＃语法对我来说效果很好：

  // TimeOut
  if (int.TryParse(ConfigurationManager.AppSettings["timeOut"], out int timeOut))
  {
     this.timeOut = timeOut;
  }

如何检查appSettings键是否存在？

9 个答案: