C＃从注册表读取十进制值

Question

i have a NumericUpDown control and want to update its contents from the registry. So far this is what i got:

this.apTime.Value = APRegsitry.GetValue("apTime").ToString();

Obviously that wont work so how do i set this.apTime to the value of the registry key?

Answer 1

I'm not entirely sure what the issue is. Are you having problems converting it to a decimal? If so try Decimal.Parse

Object obj = APRegistry.GetValue("apTime");
String str = obj != null ? obj.ToString() : "0";
Decimal value = Decimal.Parse(str);
this.apTime.Value = value;

If not can you elaborate further as to what the problem is?

EDIT Updated code to account for null return from GetValue

Answer 2

You shouldn't trust the value from the registry since a user can edit it outside your application. You need to handle the following cases:

• registry key doesn't exist
• registry key exists, but name/value doesn't exist ( null )
• you expect a string , value is not string type (eg it is an int or byte[] )
• value is a string but not parsable to decimal ( "" , "abc" )

If the key doesn't exist, RegistryKey.OpenSubKey(name) returns null. You might want to handle that and create the key. If the key exists, but not the name/value pair, then RegistryKey.GetValue(name) returns null. You can handle that by passing a default value to the overload RegistryKey.GetValue(name, defaultValue) or by using ?? .

Now, if the name/value pair exists but has an invalid value ( "" , "abc" ), you'll get an exception from Parse() . The Parse() methods (in int , decimal , DateTime , etc) have been pretty much been deprecated by TryParse() . They return false instead of throwing FormatException .

// passing the default value to GetValue()
object regValue = APRegistry.GetValue("apTime", "0");
// ...same as...
object regValue = APRegistry.GetValue("apTime") ?? "0";

decimal value;

// regValue will never be null here, so safe to use ToString()
if(decimal.TryParse(regValue.ToString(), out value))
{
    this.apTime.Value = value;
}
else
{
    // Name/pair does not exist, is empty,
    // or has invalid value (can't parse as decimal).

    // Handle this case, possibly setting a default value like this:
    this.apTime.Value = 0; 
}