Form1界面:
 public partial class Form1 : Form
    {
        string FName;            
        public Form1()
        {
            InitializeComponent();                     
        }
 private void 打开ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            OpenFileDialog openFileDialog1 = new OpenFileDialog();
            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                FName = openFileDialog1.FileName;               
                Form2 newchild = new Form2(FName);
                newchild.Show();               
            }
         }
}
Form2界面:
public partial class Form2 : Form
    {

        Form1 tempForm = new Form1();
        private string fName;
      
        public Form2( string fname)
        {
            InitializeComponent();
            
            this.fName = fname;
        }        
        public void button1_Click(object sender, EventArgs e)
        {
            if (this.radioButton1.Checked)
            {
               File fileOpen = new File(fName);               
               tempForm.textBox4.Text = fileOpen.ReadFile();
               tempForm.textBox4.AppendText("");               
              this.Close();                 
            }
        }
        public class File
        {
            string fileName;
            public File(string fileName)
            {
                this.fileName = fileName;
            }
            public string ReadFile()
            {
                try
                {
                    StreamReader sr = new StreamReader(fileName, Encoding.Default);
                    string result = sr.ReadToEnd();
                    sr.ReadLine();
                    sr.Close();
                    return result;
                }
                catch (Exception e)
                {
                    MessageBox.Show(e.Message);
                    return null;
                }           
            }
        }      
 程序执行后,Form1界面的控件textBox4不显示数据.为什么?

把Form1中的代码Form2 newchild = new Form2(FName);改成
Form2 newchild = new Form2(FName,this);
把Form2中的代码Form1 tempForm = new Form1();改成
Form1 tempForm = null;
把Form2的构造方法改成
public Form2( string fname，Form1 f1)
 {
            InitializeComponent();
            this.fName = fname;
            this.tempForm = f1;
 }

成功了,谢谢!

这块不成功 估计还是你面向对象没搞清

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