Question

C#中如何画线？鼠标点击一下，记下第一个点，鼠标抬起时记录第二个点，同时停止画线

Answer 1

用GDI+

Graphics gra;
Point firstpoint;
Point secondpoint;
private void Form1_Load(object sender, EventArgs e)
{
gra = this.CreateGraphics();
firstpoint = new Point(0, 0);
secondpoint = new Point(0, 0);
}

private void Form1_MouseDown(object sender, MouseEventArgs e)
{
firstpoint.X = e.X;
firstpoint.Y = e.Y;
}

private void Form1_MouseUp(object sender, MouseEventArgs e)
{
secondpoint.X = e.X;
secondpoint.Y = e.Y;
gra.DrawLine(Pens.Black, firstpoint, secondpoint);
}

追问

我想知道在画线的过程中，如何随着鼠标的移动而画线，当鼠标放下的时候，线画好了（只是一条线，而不是一大片扫过的部分）。

追答

要那个耀眼的效果啊，麻烦而且累人
再加一个控件，比如说PictureBox，用它的事件和graphic去画，加一个mousemove事件，再弄一个开关，画法与上面一样，最后画好了再清picturebox，画到form上去：

class Line
{
public Line(Point pt1, Point pt2)
{
this.pt1 = pt1;
this.pt2 = pt2;
}
public Point pt1;
public Point pt2;
}
Graphics grapic;
Point firstpoint;
Point secondpoint;
bool moving = false;
List lines = new List();
private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
{
pictureBox1.Refresh();
pictureBox1.BackColor = Color.Transparent;
secondpoint.X = e.X;
secondpoint.Y = e.Y;
lines.Add(new Line(firstpoint, secondpoint));
foreach (Line line in lines)
{
grapic.DrawLine(Pens.Black, line.pt1, line.pt2);
}
moving = false;
}

private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
{
pictureBox1.Refresh();
foreach (Line line in lines)
{
grapic.DrawLine(Pens.Black, line.pt1, line.pt2);
}
firstpoint.X = e.X;
firstpoint.Y = e.Y;
moving = true;
}

private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
{
if (moving)
{

pictureBox1.Refresh();
foreach (Line line in lines)
{
grapic.DrawLine(Pens.Black, line.pt1, line.pt2);
}
pictureBox1.BackColor = Color.Transparent;
grapic.DrawLine(Pens.Black, firstpoint, new Point(e.X, e.Y));
}

}

Answer 2

你不是知道了吗？就按你理解的写成C#语句就可以了
分别是mousedown记下鼠标位置，mouseup事件中得到鼠标位置。然后drawline就可以了

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