C#:FieldInfo.GetValue返回null

Question

我有问题通过Reflection在变量o中检索我的控件f2:

public partial class Form1 : Form
{
    private Form2 f2;

    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        Form2 f2 = new Form2();
        f2.Show();
    }

    private void button2_Click(object sender, EventArgs e)
    {
        Type controlType = this.GetType();
        FieldInfo f = controlType.GetField("f2", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
        object o = f.GetValue(this); // o == null;
    }
}

Answer 1

那是因为您创建了一个名为f2in 的局部变量,button1_Click但从未将类成员f2设置为该新实例:

private void button1_Click(object sender, EventArgs e)
{
    // Creates a new variable called f2 that is local to the function
    Form2 f2 = new Form2();

    // To store the local instance to the class member, you need to un-comment
    // this.f2 = f2;        
    // or change the previous line of code to:
    // f2 = new Form2();

    // Show the local form
    f2.Show();
}

因此,类级别中存在空值f2.

我也假设你在这个例子中只是玩反射.如果这不是严格的反射测试......你应该直接参考this.f2,而不是通过反射.