了解C#中的布尔键用法 [英] to understand the Boolean key use in C#

问题描述

大家好，
我正在尝试在C#.Net中执行以下代码

Hi All,
I m trying to execute following code in C# .Net

private void txtRollNumber_KeyDown(object sender, KeyEventArgs e)
{
    label1.Enabled = true;
    bool result = false;
    if (txtRollNumber.Text == false)                    
    {                    
        label1.Text="Please Enter value in Roll Number";
        txtRollNumber.Select();
    }
    else
    {
        txtname.Select();
    }
}       

但它在这一行中显示错误(txtRollNumber.Text == false)，它表明

运算符"=="不能应用于类型为字符串"和布尔"的操作数
请帮我该怎么办?

谢谢&问候
Indrajit

but it shows an error in this line (txtRollNumber.Text == false) it shows that

Operator ''=='' cannot be applied to operands of type ''string'' and ''bool''
Please help what should I do ?

Thanks & Regards
Indrajit

推荐答案

您可以将字符串与布尔值进行比较，就像对苹果和计算机(:rolleyes:)一样. 要解决此问题，请将一个表达式与另一个相同类型的表达式进行比较，例如

You can compare strings with booleans like you may do with apples and computers ( :rolleyes: ).
To fix the issue compare an expression with another of the same type, e.g.

// string to string comparison
if ( txtRollNumberTxt.Text == String.Empty )

或

or

// bool to bool comparison
if ( String.IsNullOrEmpty(txtRollNumberTxt.Text) == true )

请注意，上面的代码可能更简洁地表示为

Please note the above code maybe expressed more concisely with

if ( String.IsNullOrEmpty(txtRollNumberTxt.Text) )

尝试一下.

Try this.

private void txtRollNumber_KeyDown(object sender, KeyEventArgs e)
{
    label1.Enabled = true;
    bool result = false;
    if (string.IsNullOrWhiteSpace(txtRollNumber.Text))
    {
        label1.Text="Please Enter value in Roll Number";
        txtRollNumber.Select();
    }
    else
    {
        txtname.Select();
    }
}

还有一件事.

String.IsNullOrWhiteSpace与String.IsNullOrEmpty.

String.IsNullOrWhiteSpace背后的代码是这样描述的:

One more thing.

String.IsNullOrWhiteSpace vs String.IsNullOrEmpty.

The code behind String.IsNullOrWhiteSpace is described like this:

return String.IsNullOrEmpty(value) || value.Trim().Length == 0;

SIMPLEST ...

SIMPLEST...

if ( txtRollNumberTxt.Text.Trim() == String.Empty )
{
    label1.Text="Please Enter value in Roll Number";
    txtRollNumber.Select();
}
.
.
.

这篇关于了解C#中的布尔键用法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！