使用if条件时出错 [英] Error using the if condition

问题描述

错误。



请更正下面'if'的编码

  if （ddl_Moratorium.SelectedItem。 Text  =  无）
 txt_Morat_Mths.Enabled = false; 
  else  
 txt_Morat_Mths.Enabled = true; 

谢谢

解决方案

没有人真正指出问题是if语句中的语法错误。

单个 = 表示分配，如

  int  i =  0 ; 

为了比较相等，你需要使用double ==



因此，您只需添加第二个 =

  if （ddl_Moratorium.SelectedItem.Text ==   NONE）
 txt_Morat_Mths.Enabled =  false ; 
  else  
 txt_Morat_Mths.Enabled =  true ; 

正如已经指出的那样，这是不安全的，因为如果ddl_Moratorium.SelectedItem为null，你将得到一个NullReference错误。

解决方案5为您提供最易读的代码。



您也可以将代码更改为单行代码，但它当然不太可读。 :)

 txt_Morat_Mths.Enabled =（（ddl_Moratorium.SelectedItem！=  null ）&&（ ddl_Moratorium.SelectedItem！=   NONE））; 

  if （ddl_Moratorium.SelectedItem ==  null ）
 txt_Morat_Mths.Enabled = false; 
  else   if （ddl_Moratorium.SelectedItem。 Text  ==   NONE）
 txt_Morat_Mths.Enabled = false; 
  else  
 txt_Morat_Mths.Enabled = true; 

试试这个

  if （ddl_Moratorium.SelectedItem.Text ==   NONE）
 txt_Morat_Mths.Enabled =  false ; 
  else  
 txt_Morat_Mths.Enabled =  true ; 

或

  if （ddl_Moratorium .SelectedItem.Text.Equals（  NONE））
 txt_Morat_Mths.Enabled = 假; 
  else  
 txt_Morat_Mths.Enabled =  true ; 

Error.

Please correct the coding below its around the 'if'

if (ddl_Moratorium.SelectedItem.Text ="NONE")
                txt_Morat_Mths.Enabled = false;
            else
                txt_Morat_Mths.Enabled = true;

Thanks

解决方案

No one has actually pointed out that the problem is a syntax error in the if statement.
A single = means assignment, as in

int i = 0;

In order to compare equality you need to use double ==

So you could correct your code by simply adding a second =

if (ddl_Moratorium.SelectedItem.Text == "NONE")
    txt_Morat_Mths.Enabled = false;
else
    txt_Morat_Mths.Enabled = true;

As has been pointed out, this is not safe as you will get a NullReference error if ddl_Moratorium.SelectedItem is null.
Solution 5 gives you the most readable code.

You can also change your code to a one liner, but it is of course less readable. :)

txt_Morat_Mths.Enabled = ((ddl_Moratorium.SelectedItem != null) && (ddl_Moratorium.SelectedItem != "NONE"));

if (ddl_Moratorium.SelectedItem == null)
    txt_Morat_Mths.Enabled = false;
else if (ddl_Moratorium.SelectedItem.Text == "NONE")
    txt_Morat_Mths.Enabled = false;
else
    txt_Morat_Mths.Enabled = true;

Try this

if (ddl_Moratorium.SelectedItem.Text == "NONE")
 txt_Morat_Mths.Enabled = false;
else
 txt_Morat_Mths.Enabled = true;

or

if (ddl_Moratorium.SelectedItem.Text.Equals("NONE"))
 txt_Morat_Mths.Enabled = false;
else
 txt_Morat_Mths.Enabled = true;

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