string.IsNullOrEmpty 使用 Trim()

Question

I want to remove the first line:

                 !string.IsNullOrEmpty(cell.Text) 

will this cause any issue?

I ran across this in some code:

                if ((id % 2 == 0)
                    && !string.IsNullOrEmpty(cell.Text)
                    && !string.IsNullOrEmpty(cell.Text.Trim())
                    )

I think the first string.IsNullOrEmpty would return false on a string with spaces
and the line with Trim() takes care of that, so the first IsNullOrEmpty is useless

But before I remove the line without the trim I thought I'd run it by the group.

Answer 1

如果cell.Text为null，则没有第一次检查就会出现异常。

Answer 2

In .NET 4.0:

if (id % 2 == 0 && !string.IsNullOrWhiteSpace(cell.Text))
{
    ...
}

In older versions you should keep the two tests because if you remove the first and cell.Text is null, you will get a NRE on the second when you try to invoke .Trim on a null instance.

Or you could also do this:

if (id % 2 == 0 && string.IsNullOrWhiteSpace((cell.Text ?? string.Empty).Trim()))
{
    ...
}

or even better, you could write an extension method for the string type that will do this so that you could simply:

if (id % 2 == 0 && !cell.Text.IsNullOrWhiteSpace())
{
    ...
}

which might look like this:

public static class StringExtensions
{
    public static bool IsNullOrWhiteSpace(this string value)
    {
        return string.IsNullOrEmpty((value ?? string.Empty).Trim());
    }
}

Answer 3

The first IsNullOrEmpty catches null values before they throw a NullReferenceException with Trim().

However, there is a better way:

if ((id % 2 == 0) && !string.IsNullOrWhiteSpace(cell.Text))

Answer 4

You can use extension method like this:

/// <summary>
/// Indicates whether the specified string is null or empty.
/// This methods internally uses string.IsNullOrEmpty by trimming the string first which string.IsNullOrEmpty doesn't.
/// .NET's default string.IsNullOrEmpty method return false if a string is just having one blank space.
/// For such cases this custom IsNullOrEmptyWithTrim method is useful.
/// </summary>
/// <returns><c>true</c> if the string is null or empty or just having blank spaces;<c>false</c> otherwise.</returns> 
public static bool IsNullOrEmptyWithTrim(this string value)
{
    bool isEmpty = string.IsNullOrEmpty(value);
    if (isEmpty)
    {
        return true;
    }
    return value.Trim().Length == 0;
}

Answer 5

We can use null conditional:

!string.IsNullOrEmpty(cell?.Text?.Trim())

Note "?" before reading the next property and trim.

Answer 6

我相信测试是为了确保cell.text首先不是null ...如果是这样，试图绕过它并得到只是cell.text.trim（）会因为你无法对空字符串进行修剪而窒息。

Answer 7

为什么不使用!string.IsNullOrWhitespace(call.Text)并删除前两个检查？

Answer 8

You cannot remove just the first IsNullOrEmpty as the cell.Text could be null and thus calling Trim on it would throw and exception. Use IsNullOrWhiteSpace if you are using .Net 4.0 or leave both checks.

if ((id % 2 == 0) && !string.IsNullOrWhiteSpace(cell.Text))

Answer 9

If cell.Text is null, the expression string.IsNullOrEmpty(cell.Text.Trim()) will throw an exception since it is trying to run method Trim() on cell.

Much more readble if condition would be: cell.Text!=null && cell.Text.Trim()!=""