画两条线，为何只显示方法二的线条，方法一的线条哪去了，

Question

Pen p = new Pen(Color.Black, 2);
        //方法一：
        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics G = e.Graphics;
            G.DrawLine(p, 30, 30, 100, 30);
        }
        //方法二：
        protected override void OnPaint(PaintEventArgs e)
        {
            Graphics g = e.Graphics;
            g.DrawLine(p, 30, 100, 100, 100);
        }

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杲大胜 ...........勤!能!补!拙!........ 勤!勤!勤!.............

Answer 1

OnPaint应该要触发Paint事件，所以你应该再次调用父函数的方法：

 protected override void OnPaint(PaintEventArgs e)
        {
            Graphics g = e.Graphics;
            g.DrawLine(p, 30, 100, 100, 100);
            base.OnPaint(e);
        }

---

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Answer 2

 

试过了,加了base.OnPaint(e)仍然没有显示方法一的线条，两个方法是否不能同时使用。

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杲大胜 ...........勤!能!补!拙!........ 勤!勤!勤!.............

Answer 3

是两条线，你看结果：

public partial class Form1 : Form
    {
        Pen p = new Pen(Color.Black, 2);
 
        public Form1()
        {
            InitializeComponent();
        }
 
        private void Form1_Load(object sender, EventArgs e)
        {
 
        }
 
        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics G = e.Graphics;
            G.DrawLine(p, 30, 30, 100, 30);
        }
        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);
            p = new Pen(Brushes.Red);
            Graphics G = e.Graphics;
            G.DrawLine(p, 30, 100, 100, 30);
        }
    }

---

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