_textChanged事件给我错误“对象引用未设置为对象的实例”

Question

我是C＃的新手，所以仍然找到我的方法。

我有一个按钮，我只想在用户输入文本到文本框时启用。 我得到这个错误 - “对象引用未设置为对象的实例”。

下面是相关的代码（不使用和变量）：

public MainWindow() 
    { 
     MessageBox.Show("Make sure to edit Settings tab."); 
     InitializeComponent(); 
     if (startTextBox.Text == "0") // Checks to see if a textbox has some text other than zero. if no than the user cannot press button1 yet. 
     { 
      button1.IsEnabled = false; 
     } 
     else 
     { 
      button1.IsEnabled = true; 
     } 

    } 

    private void Window_Loaded(object sender, RoutedEventArgs e) 
    { 

     if (radioButton1.IsChecked == false) 
     { 
      label17.Content = "No Hourly wage was set."; 
     } 

    } 

    private void add(object sender, RoutedEventArgs e) /// here is a very long method so I've removed its content. 


    } 


    public void printTime() 
    { 

     int Sum = (this.EndInt - this.StartInt); 
     int Money = (Sum * this.L1001); 


     label16.Content = Sum; 
     label17.Content = Money; 
     if ((textBox1.Text == "0") && ((textBox2.Text == "0") || (textBox3.Text == "0"))) 
     { 
      label17.Content = "No Hourly wage was set."; 
     } 
    } 

    public void printTime2() 
    { 

     int Sum = (this.EndInt - this.StartInt); 
     MessageBox.Show("Is it possible that you've worked - " + Sum + " Hours?"); 
    } 

    public void printTime3() 
    { 

     int Sum = (this.EndInt - this.StartInt); 
     int Money = (Sum * this.L1001); 

     label16.Content = Sum; 
     label17.Content = Money; 
     if (textBox1.Text == "0") 
     { 
      label17.Content = "No Hourly wage was set."; 
     } 
    } 


    public int Convert(String S) 
    { 
     int i = int.Parse(S); 
     return i; 
    } 


    // Input Validation For Excepting Integers Only! 
    private void input(object sender, TextCompositionEventArgs e) 
    { CheckIsNumeric(e); } 
    private void CheckIsNumeric(TextCompositionEventArgs e) 
    { 
     int result; if (!(int.TryParse(e.Text, out result) || e.Text == ".")) 
     { e.Handled = true; MessageBox.Show("Numbers Only"); } 

    } 


    private void startTextBox_TextChanged(object sender, TextChangedEventArgs e) 
    { 

     button1.IsEnabled = true; 
    } 




} 

}

Answer 1

它的范围问题。你没有显示button1的定义。但是在你的事件处理程序startTextBox_TextChanged中，button1定义无处可寻（实际上它也需要实例化）。由于您尝试在尚未实例化的对象（button1）上调用方法，因此抛出了该异常。

如果您发布的不仅仅是这些片段，我或其他人可能会进一步帮助您。