如何检查对象为空或为空 [英] How to check an object is empty or null

问题描述

大家好，
这是supriya.我有一个问题.在我的代码中，一个函数返回一个对象(用户定义).但是我不知道如何检查该对象是否为空或为空.
我的代码是

Hi all,
this is supriya.I have a problem .In my code a function returns an object(User Defined).But i don''t Know how to check whether this Object is empty or null.
My code is

txtAgeSex.Text = 
           objCommonNSBussinessObjects = objClinicalSummaryPresenter.getData(pIPno, gappln_data);
           objectToScreen(objCommonNSBussinessObjects);

private void objectToScreen(CommonNSBussinessObjects objCommonNSBussinessObjects)
        {
            txtMRNo.Text = Convert.ToString(objCommonNSBussinessObjects.mrno);
            txtRoom.Text = Convert.ToString(objCommonNSBussinessObjects.Room);
            txtWard.Text = Convert.ToString(objCommonNSBussinessObjects.Ward);
            txtAdmDate.Text = Convert.ToString(objCommonNSBussinessObjects.AdmissionDate);
            txtDocCode.Text = Convert.ToString(objCommonNSBussinessObjects.DocCode);
            txtDocName.Text = Convert.ToString(objCommonNSBussinessObjects.DocName);
            txtPatName.Text = Convert.ToString(objCommonNSBussinessObjects.PatNAme);
            txtAgeSex.Text = Convert.ToString(objCommonNSBussinessObjects.AgeSex);

        }

objCommonNSBussinessObjects

是getData(.....)方法返回的对象.
有时getData(...)返回Null值.

我收到错误

is an object returned by getData(.....) method.
sometimes getData(...) returns Null Value.

i am getting an error

Object reference not set to an instance of an object.

帮助我检查对象是否为空

help me in Cheking the object is empty or not

推荐答案

if (objCommonNSBussinessObjects != null)
{
  //code 
}

对于任意类型，没有空"这样的概念.甚至没有"null".如果满足以下条件，则可以将该对象与null进行比较:

1)该对象属于引用类，请参见 http://msdn .microsoft.com/en-us/library/t63sy5hs％28v = VS.100％29.aspx [ http://msdn.microsoft.com/en-us/library/1t3y8s4s.aspx [ ^ ].

在进行任何编程之前，建议您阅读该语言和.NET手册.这些事实非常基础.

—SA

There is no such concept as "empty" for an arbitrary type; and not even "null". The object can be compared to null if:

1) This object is of the reference class, see http://msdn.microsoft.com/en-us/library/t63sy5hs%28v=VS.100%29.aspx[^];

or

2) This object is of nullable type, see http://msdn.microsoft.com/en-us/library/1t3y8s4s.aspx[^].

Looks, before programming anything, it''s advisable to read the language and .NET manual. These facts are quite elementary.

—SA

避免错误的一种方法是使用null coalesce运算符-??.
例如

One way to avoid the error could be to use the null coalesce operator - ??.
e.g.

txtMRNo.Text = Convert.ToString(objCommonNSBussinessObjects.mrno??string.empty);
txtRoom.Text = Convert.ToString(objCommonNSBussinessObjects.Room??string.empty);

另一种方法是将您的值与null进行比较.

Another way would be to compare your values against null.

private void objectToScreen(CommonNSBussinessObjects objCommonNSBussinessObjects)
        { if (objCommonNSBussinessObjects != null){
              txtMRNo.Text = Convert.ToString(objCommonNSBussinessObjects.mrno);
              txtRoom.Text = Convert.ToString(objCommonNSBussinessObjects.Room);
              txtWard.Text = Convert.ToString(objCommonNSBussinessObjects.Ward);
              txtAdmDate.Text = Convert.ToString(objCommonNSBussinessObjects.AdmissionDate);
              txtDocCode.Text = Convert.ToString(objCommonNSBussinessObjects.DocCode);
              txtDocName.Text = Convert.ToString(objCommonNSBussinessObjects.DocName);
              txtPatName.Text = Convert.ToString(objCommonNSBussinessObjects.PatNAme);
              txtAgeSex.Text = Convert.ToString(objCommonNSBussinessObjects.AgeSex);
            }
        }

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