铸造新System.Windows.Forms.Control的对象System.Windows.Forms.Textbox [英] casting new System.Windows.Forms.Control object to System.Windows.Forms.Textbox

问题描述

我得到一个InvalidArgumentException同时播送控制到System.Windows.Forms.Textbox：

无法投类型的对象'系统。 Windows.Forms.Control为键入'System.Windows.Forms.TextBox。

  System.Windows.Forms.Control的控制=新System.Windows.Forms.Control的（）; 
 control.Width = currentField.Width; 
 
 //这里来的错误
（（System.Windows.Forms.TextBox）控制）。文本= currentField.Name; 
  

我这样做，是因为我有不同的控件（文本框，MaskedTextBox中，dateTimePicker的...）这将被动态地添加到一个面板和具有相同的基本性质（大小，位置 - >控制）

为什么没有铸造可能

解决方案

演员，因为控制的不是失败，一个文本框 的。你可以把一个文本框作为对照（上涨类型层次结构），但没有任何控制为文本框。为了制定共同的属性，你可以只是把一切都为控制，并设置它们，而你必须创建要事先用实际控制：

 文本框TB =新的TextBox（）; 
 tb.Text = currentField.Name; 
 
控制C =（控制）TB; //这个工程，因为每一个文本框也是控制
 //但并不是每个控制是一个文本框，尤其不要
 //如果你显式的指定使它*不*一个文本框
 C .WIDTH = currentField.Width; 
  

i get an InvalidArgumentException while casting Control to System.Windows.Forms.Textbox:

Unable to cast object of type 'System.Windows.Forms.Control' to type 'System.Windows.Forms.TextBox'.

System.Windows.Forms.Control control = new System.Windows.Forms.Control();
control.Width = currentField.Width;

//here comes the error
((System.Windows.Forms.TextBox)control).Text = currentField.Name;

I am doing this, because I have different Controls (Textbox, MaskedTextbox, Datetimepicker...), which will dynamically be added to a panel and have the same basic properties (Size, Location... -> Control)

Why isn't the cast possible?

解决方案

The cast fails because control is not a TextBox. You can treat a TextBox as a control (higher up the type hierarchy) but not any Control as a TextBox. For setting common properties you can just treat everything as Control and set them whereas you have to create the actual controls you want to use beforehand:

TextBox tb = new TextBox();
tb.Text = currentField.Name;

Control c = (Control)tb; // this works because every TextBox is also a Control
                         // but not every Control is a TextBox, especially not
                         // if you *explicitly* make it *not* a TextBox
c.Width = currentField.Width;

这篇关于铸造新System.Windows.Forms.Control的对象System.Windows.Forms.Textbox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！