c# - string.IsNullOrEmpty(string) 与 string.IsNullOrWhiteSpace(string)

Question

在 .NET 4.0 及更高版本中存在 string.IsNullOrWhiteSpace(string) 时，在检查字符串时使用 string.IsNullOrEmpty(string) 是否被视为不良做法？

Answer 1

最佳做法是选择最合适的。

.Net Framework 4.0 Beta 2 has a new IsNullOrWhiteSpace() method for strings which generalizes the IsNullOrEmpty() method to also include other white space besides empty string.

The term “white space” includes all characters that are not visible on screen. For example, space, line break, tab and empty string are white space characters*.

引用:Here

For performance, IsNullOrWhiteSpace is not ideal but is good. The method calls will result in a small performance penalty. Further, the IsWhiteSpace method itself has some indirections that can be removed if you are not using Unicode data. As always, premature optimization may be evil, but it is also fun.

引用:Here

查看源码(引用源.NET Framework 4.6.2)

IsNullorEmpty

[Pure]
public static bool IsNullOrEmpty(String value) {
    return (value == null || value.Length == 0);
}

IsNullOrWhiteSpace

[Pure]
public static bool IsNullOrWhiteSpace(String value) {
    if (value == null) return true;

    for(int i = 0; i < value.Length; i++) {
        if(!Char.IsWhiteSpace(value[i])) return false;
    }

    return true;
}

示例

string nullString = null;
string emptyString = "";
string whitespaceString = "    ";
string nonEmptyString = "abc123";

bool result;

result = String.IsNullOrEmpty(nullString);            // true
result = String.IsNullOrEmpty(emptyString);           // true
result = String.IsNullOrEmpty(whitespaceString);      // false
result = String.IsNullOrEmpty(nonEmptyString);        // false

result = String.IsNullOrWhiteSpace(nullString);       // true
result = String.IsNullOrWhiteSpace(emptyString);      // true
result = String.IsNullOrWhiteSpace(whitespaceString); // true
result = String.IsNullOrWhiteSpace(nonEmptyString);   // false