.net画图异常

Question

你是画在picturebox上吧 而没有给Picturebox。Image 赋值吧

Answer 1

怎么判断pictureBox1.Image是否为null？ if(pictureBox1.Image==null)
{
 MessageBox.Show("没有图片")；
}
已经在pictureBox1中画过图像，为什么还会出现NULL例外？这个需要看你的代码。你贴上来

Answer 2

本来就应该先判断pictureBox1.Image是否null，再传值，

Answer 3

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;namespace WindowsApplication2
{
    public partial class Form1 : Form
    {
        Pen MyPen = new System.Drawing.Pen(System.Drawing.Color.Red, 1);
        PointF pStart;
        PointF pEnd;
        PointF pWork;
        Boolean working;
        Boolean brushmode;
        String dmode = "line";
        
        void Drawshape(Graphics e,PointF startp,PointF endp,Boolean brushmode,Pen penmode,String dmode)
        {
            Rectangle rect1=new Rectangle ((int)startp.X ,(int)startp.Y,(int)(endp.X -startp .X ),(int)(endp.Y -startp.Y ));
            switch (dmode )
            {
                case "line":
                e.DrawLine(penmode,startp.X,startp.Y,endp.X ,endp.Y);
                break ;
                case "rect":
                if(brushmode==true) e.FillRectangle(penmode.Brush ,rect1);
                    else e.DrawRectangle(penmode,rect1);
                break;
                case "circle":
                if(brushmode ==true ) e.FillEllipse(penmode.Brush,rect1);
                else e.DrawEllipse(penmode,rect1);
                    break;
                default:break;
            }
        }
        public Form1()
        {
            InitializeComponent();
        }        private void Form1_Load(object sender, EventArgs e)
        {
            System.Drawing.Drawing2D.HatchBrush brush2 = new
            System.Drawing.Drawing2D.HatchBrush(
            System.Drawing.Drawing2D.HatchStyle.DarkDownwardDiagonal,
            Color.Brown);
            //BtnSetColor.BackColor =Color .MediumBlue;
        }        private void BtnSetColor_Click(object sender, EventArgs e)
        {
            colorDialog1.ShowDialog();
            BtnSetColor.BackColor = colorDialog1.Color;
        }        private void BntClear_Click(object sender, EventArgs e)
        {
            pictureBox1.CreateGraphics().Clear(Color.White);
        }        private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            working = true;
            pStart.X = e.X;
            pStart.Y = e.Y;
           toolStripStatusLabel1 .Text  = "[" + e.X + "," + e.Y + "]";
        }        private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
        {
           if(working==true )
           {
               pEnd.X =e.X;
               pEnd .Y=e.Y;
               MyPen.Color=BtnSetColor.BackColor ;
               MyPen.Width=(int)numericUpDown1.Value;
               brushmode=checkBox1 .Checked ;
               if(radioButton1 .Checked==true )
                   MyPen .DashStyle =System .Drawing .Drawing2D .DashStyle .Solid ;
                if(radioButton2 .Checked==true )
                   MyPen .DashStyle =System .Drawing .Drawing2D .DashStyle .Dot ;
                if(radioButton3 .Checked==true )
                   MyPen .DashStyle =System .Drawing .Drawing2D .DashStyle .Dash;
                if(radioButton4.Checked==true )
                   MyPen .DashStyle =System .Drawing .Drawing2D .DashStyle .Custom ;
                if(radioButton5 .Checked==true )
                   MyPen .DashStyle =System .Drawing .Drawing2D .DashStyle .DashDotDot;
                if(radioButton6 .Checked==true )
                   MyPen .DashStyle =System .Drawing .Drawing2D .DashStyle .DashDot;
                 if(radioButton7 .Checked==true )
                     dmode ="line";
                 if(radioButton8 .Checked==true )
                     dmode ="circle";
                 if(radioButton9.Checked==true )
                     dmode ="rect";
                 if(radioButton10 .Checked==true )
                     MyPen .Brush =new System .Drawing .Drawing2D .HatchBrush (
                         System.Drawing.Drawing2D.HatchStyle .DarkDownwardDiagonal ,
                         MyPen.Color );
                 if(radioButton11 .Checked==true )
                     MyPen .Brush =new 
                         System .Drawing .Drawing2D .HatchBrush (
                         System.Drawing.Drawing2D.HatchStyle .Cross ,MyPen .Color );
                 if(radioButton12 .Checked==true )
                     MyPen .Brush =new SolidBrush(MyPen .Color );
               Drawshape (pictureBox1 .CreateGraphics (),
               pStart ,pEnd,brushmode ,MyPen ,dmode );
               working =false ;
           }        }        private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
            if (working == true)
            {
                pWork.X = e.X;
                pWork.Y = e.Y;
                toolStripStatusLabel1.Text = "[" + e.X + "," + e.Y + "]";
            }
        }       //前面为一个简单画图程序        private void button1_Click(object sender, EventArgs e)
        {//剪切按钮
                Clipboard.SetDataObject(pictureBox1.Image, true);
                pictureBox1.CreateGraphics().Clear(pictureBox1.BackColor);
           
        }        private void button2_Click(object sender, EventArgs e)
        {//复制按钮                Clipboard.SetDataObject(pictureBox1.Image, true);
            
            
        }        private void button3_Click(object sender, EventArgs e)
        {//粘贴按钮
            IDataObject clipbord_data;
            Image tmp;
            clipbord_data = Clipboard.GetDataObject();
            if (clipbord_data.GetDataPresent(DataFormats.Bitmap))
            {
                tmp = (Image)clipbord_data.GetData(DataFormats.Bitmap);
                pictureBox2.CreateGraphics().DrawImage(tmp, 0, 0);
            }
        }
   }
}

Answer 4

pictureBox1.Image不是BOOL型，仍然发生错误