變數'<variablename>' 已在指派值之前使用 (Visual Basic 錯誤) 發行項 2008/08/21 更新:2007 年 11 月 變數已在指派值之前使用,而造成 NullReferenceException。 錯誤ID:BC42109 若要更正這個錯誤 確定已指派變數的值。 請參閱 概念 Visual Basic 中的變數宣告 參考 疑難排解例外狀況:System.NullRefer...
在Visual Basic (VB) 中,赋值是将一个值或表达式的结果存储到一个变量中的过程。赋值语句的基本语法是使用 = 运算符,将右侧的值或表达式的结果赋给左侧的变量。 赋值的基本语法 vb variable = value_or_expression variable:需要赋值的变量名。 value_or_expression:可以是常量、变量、表达式或函数调用结果。 赋值...
Visual Basic 中的變數 變數宣告 物件變數 物件變數宣告 物件變數宣告 如何:存取物件的成員 物件變數指派 物件變數值 物件變數值 如何:參考物件目前的執行個體 如何:決定物件變數參考的類型 如何:判斷兩個物件是否關聯 如何:判斷兩個物件是否相同 區域類型推斷 ...
局部变量是在过程中声明的变量。 成员变量是 Visual Basic 类型的成员,在模块级别声明,在类、结构或模块中声明,但不在该类、结构或模块内部的任何过程中声明。 共享变量和实例变量 在类或结构中,成员变量的类别取决于它是否是共享的。 如果它是用“共享”关键字声明的,则它是一个共享变量,并且它存在于类或结构...
I am new to VB.NET 2012. I have been using VFP9 for a long time. In VFP(, i can create a global variable that will be available thought the entire...
The Static variable totalSales is initialized to 0 only one time. Each time that you enter updateSales, totalSales still has the most recent value that you calculated for it. The Static modifier can be used in this context: Dim Statement See also Shadows Shared Lifetime in Visual Basic Var...
A multithreaded application usually has resources that can be accessed from multiple threads; for example, a global variable that is incremented or decremented by multiple threads. It is sometimes desirable to prevent multiple threads from concurrently altering the state of a ...
Visual Basic .NET 要求始终创建 COM 对象的实例,然后才能使用其方法。 若要在 Visual Basic 中使用这些方法,请声明所需类的变量,并使用新关键字将对象分配给对象变量。 如果要确保只创建一个类实例,则可以使用Shared关键字。 VB复制 ' Class level variable.SharedDBEngineAsNewDAO.DBEngineSubDAOOpenRecordset()Dim...
In Excel for Mac, a new Visual Basic Editor was introduced in October 2017. With this new VB editor, there's an issue with creating object declarations by choosing from the drop-down menu at the top of the code window. If you click t...
The big advantage of implementing the ObjectControl interface is that you can declare a class-level variable to reference the ObjectContext object. That way you don't have to write thegetObjectContextcall in each method. Instead, you obtain the reference during theObjectControl_Activateevent and re...