为什么?

Question

你的m变量在你new的时候没有赋值，当然为空。一个对象在new时只是调用其构造函数。对于string这样的对象并不会有一个初始值。

Answer 1

namespace data3
{
/// <summary>
/// Summary description for zhuc1.
/// </summary>
         zhuc1是一个窗口
public class zhuc1 : System.Windows.Forms.Form
{
public string yonghm;
                  public System.Windows.Forms.TextBox yonghumtextBox;
          private void InitializeComponent()
{                            // yonghumtextBox
// 
this.yonghumtextBox.BorderStyle = System.Windows.Forms.BorderStyle.FixedSingle;
this.yonghumtextBox.Location = new System.Drawing.Point(144, 80);
this.yonghumtextBox.MaxLength = 10;
this.yonghumtextBox.Name = "yonghumtextBox";
this.yonghumtextBox.Size = new System.Drawing.Size(112, 21);
this.yonghumtextBox.TabIndex = 5;
this.yonghumtextBox.Text = "";
this.yonghumtextBox.TextChanged += new System.EventHandler(this.yonghumtextBox_TextChanged);
}
在yonghumtextBox输入文字.......
单击"下一步"按钮:
private void xiaybB_Click(object sender, System.EventArgs e)
{
                        yonghm=yonghumtextBox.Text;
                   }
}
}                   zhuc2是另一个窗口
namespace data3
{
/// <summary>
/// Summary description for zhuc3.
/// </summary>
public class zhuc3 : System.Windows.Forms.Form
{
public string filename;private void liulB_Click(object sender, System.EventArgs e)
{
if(folderBrowserDialog1.ShowDialog()==DialogResult.OK)
{
pathtextBox.Text=folderBrowserDialog1.SelectedPath;
zhuc1 zuc1=new zhuc1();
filename=zuc1.yonghum;//出错!yonghum为空
                                     pathtextBox.AppendText(filename);
}
                           }
         }
}
xiaybB_Click函数在liulB_Click前已执行,调试时看yonghum已成功赋植
但在liulB_Click函数 中yonghum为空.