网站建设开发协议/百度一下你就知道官网新闻

17.2.10 重绘

先看以下例子：

【例 17.28】【项目：code17-028】绘制填充矩形。

private void button1_Click(object sender, EventArgs e)

{

Graphics g = this.CreateGraphics();

g.FillRectangle(new SolidBrush(Color.Blue), new Rectangle(260, 20, 100, 100));

}

private void Form1_Load(object sender, EventArgs e)

{

Graphics g = this.CreateGraphics();

g.FillRectangle(new SolidBrush(Color.Red), new Rectangle(20, 20, 100, 100));

}

private void Form1_Paint(object sender, PaintEventArgs e)

{

Graphics g = this.CreateGraphics();

g.FillRectangle(new SolidBrush(Color.Green), new Rectangle(140, 20, 100, 100));

}

这个例子在窗体Load、窗体Paint、按钮Click时分别绘制了红色、绿色、蓝色填充的矩形。

当运行时：

图17-31 运行时只显示绿色矩形

按下按钮时：

图17-32 显示绿色和蓝色矩形

最小化又恢复后：

图17-33 显示绿色矩形

原本的计划是：1、在Load的时候绘制一个红色正方形；2、在Paint的时候绘制一个绿色正方形；3、在按下按钮的时候绘制一个蓝色正方形；一共三个矩形。

运行后窗体上只显示了绿色而没有显示红色矩形，因为窗口Load事件之后是Paint事件，而Paint执行的时候将界面刷新了，对整个窗口进行了重绘：先是清除之前绘制的内容，然后按照Paint里面代码做了绘制，所以绿色矩形正常显示，而红色矩形没有显示。同样的，最小化后再恢复窗口，也触发了窗体的Paint事件，进行了重绘，所以绿色矩形在而蓝色矩形没有了。

分析了造成矩形不显示的原因，那么针对重绘的问题，也就有了以下解决方法：只需要把绘制的图形保存下来，当重绘时在绘制出来即可。

【例 17.29】【项目：code17-029】防止重绘时图形消失。

//用来保存绘制的图形

Bitmap bmp;

Graphics g;

private void Form1_Load(object sender, EventArgs e)

{

//使图像宽度和高度与窗体相同

bmp = new Bitmap(this.Width, this.Height);

//通过图像创建Graphic

g = Graphics.FromImage(bmp);

g.FillRectangle(new SolidBrush(Color.Red), new Rectangle(20, 20, 100, 100));

ShowImg();

}

private void button1_Click(object sender, EventArgs e)

{

g.FillRectangle(new SolidBrush(Color.Green), new Rectangle(140, 20, 100, 100));

g.FillRectangle(new SolidBrush(Color.Blue), new Rectangle(260, 20, 100, 100));

ShowImg();

}

private void Form1_Paint(object sender, PaintEventArgs e)

{

ShowImg();

}

//在窗体上显示图像

private void ShowImg()

{

Graphics gPaint = this.CreateGraphics();

gPaint.DrawImage(bmp, new Point(0, 0));

}

private void Form1_FormClosing(object sender, FormClosingEventArgs e)

{

g.Dispose();

bmp.Dispose();

}

这下，窗体Load时的红色正方形以及按下按钮后的绿色和蓝色矩形，即使窗体最小化也不怕消失了。

17.2.11 绘制统计图

【例 17.30】【项目：code17-030】绘制统计图

假设知道某个公司1-4季度的经营利润情况，完成统计图的绘制。

新建一个窗体，主要使用到的控件如下：

添加4个Label控件，分别是“一季度”、“二季度”、“三季度”、“四季度”。

添加4个NumericUpDown控件，名称从 nudSeason1至 nudSeason4。

添加1个ComboBox控件，名称为cbType，代码中为它的Items增加柱状图、折线图、扇形图、环形图。

添加1个PictureBox控件，名称为pbShow，将在这里面显示统计图。

添加2个Button控件，名称分别为btnCreate和btnSave，Text属性分别为“生成”和“保存”。当按下“生成”按钮后，将在pbShow中显示统计图；当按下“保存”按钮后，将弹出保存文件对话框，设置文件名后将统计图保存下来。

具体代码如下：

Graphics g;

Bitmap bmp;

//刻度线每份对应的数量

float perScaleValue;

//原点x轴移动

int TranslateX = 40;

//原点y轴移动

int TranslateY = 40;

//季度（x轴）之间间隔

int xSpan = 60;

private void Form1_Load(object sender, EventArgs e)

{

bmp = new Bitmap(pbShow.Width, pbShow.Height);

g = Graphics.FromImage(bmp);

cbType.Items.Add("柱形图");

cbType.Items.Add("折线图");

cbType.Items.Add("扇形图");

cbType.Items.Add("环形图");

cbType.Text = cbType.Items[0].ToString();

}

private void btnCreate_Click(object sender, EventArgs e)

{

g.Clear(System.Drawing.Color.White);

switch(cbType.Text)

{

case "柱形图":

DrawAxis();

DrawBarGraph();

break;

case "折线图":

DrawAxis();

DrawLine();

break;

case "扇形图":

DrawPie();

break;

case "环形图":

DrawAnnular();

break;

default:

break;

}

pbShow.Image = bmp;

}

//绘制坐标轴

private void DrawAxis()

{

int[] seasonValue = new int[4];

seasonValue[0] = (int)nudSeason1.Value;

seasonValue[1] = (int)nudSeason2.Value;

seasonValue[2] = (int)nudSeason3.Value;

seasonValue[3] = (int)nudSeason4.Value;

//获得最大值

int seasonMax = seasonValue.Max();

//获得需要的刻度数量

int scaleCount;

scaleCount = seasonMax / 10 + 1;

//使用红色绘制坐标轴

Pen p = new Pen(System.Drawing.Color.Red, 1);

//坐标轴末尾箭头

p.EndCap = LineCap.ArrowAnchor;

int AxisYHeight;

AxisYHeight = pbShow.Height - TranslateY * 2;

perScaleValue = AxisYHeight / scaleCount;

//坐标原点

int originX = TranslateX;

int originY = pbShow.Height - TranslateY;

Point originPoint = new Point(originX, originY);

//绘制横坐标

g.DrawLine(p, originPoint, new Point(pbShow.Width - TranslateX, originY));

//绘制纵坐标

g.DrawLine(p, originPoint, new Point(originX, TranslateY));

//红色绘制坐标轴刻度

Pen pAxisY = new Pen(System.Drawing.Color.Red, 1);

Point AxisYPos;

string AxisYValue;

//在纵轴上标明刻度线，每10个刻度标注一下

for(int i = 0;i< scaleCount;i++)

{

//刻度值

AxisYValue = (i * 10).ToString();

//刻度位置

AxisYPos = new Point(20, originY - i * (int)perScaleValue - 5);

//标明刻度值

g.DrawString(AxisYValue, new Font("宋体", 10), new SolidBrush(System.Drawing.Color.Blue), AxisYPos);

//画刻度，实际0刻度线是和横坐标轴重合

g.DrawLine(pAxisY, new Point(TranslateX, originY - i * (int)perScaleValue), new Point(TranslateX + 10, originY - i * (int)perScaleValue));

}

//绘制柱状图

private void DrawBarGraph()

{

//标注每个季度

int[] seasonValue = new int[4];

seasonValue[0] = (int)nudSeason1.Value;

seasonValue[1] = (int)nudSeason2.Value;

seasonValue[2] = (int)nudSeason3.Value;

seasonValue[3] = (int)nudSeason4.Value;

string[] seasonName = { "一季度", "二季度", "三季度", "四季度" };

//立柱（矩形）的左上角坐标点

int recX, recY;

//循环画四个矩形

for(int i = 0;i<4;i++)

{

recX = (i + 1) * xSpan;

recY = pbShow.Height - TranslateY - (int)(seasonValue[i] / 10 * perScaleValue);

g.FillRectangle(new SolidBrush(Color.Blue), new Rectangle(recX, recY, 40, (int)(seasonValue[i] / 10 * perScaleValue)));

}

//标出每个季度

int strX, strY;

for(int i =0;i<4;i++)

{

strX = (i + 1) * xSpan - 5;

strY = pbShow.Height - TranslateY + 10;

g.DrawString(seasonName[i], new Font("黑体", 10), new SolidBrush(Color.Blue), new Point(strX, strY));

}

//绘制折线图

private void DrawLine()

{

//标注每个季度

int[] seasonValue = new int[4];

seasonValue[0] = (int)nudSeason1.Value;

seasonValue[1] = (int)nudSeason2.Value;

seasonValue[2] = (int)nudSeason3.Value;

seasonValue[3] = (int)nudSeason4.Value;

string[] seasonName = { "一季度", "二季度", "三季度", "四季度" };

//先要获得每个值所在的坐标点

//为了显眼，绘制点的显示为一个直径为8的蓝色圆形

int signX, signY;

//将每个坐标点存入数组，画折线时候需要

Point[] pointSign = new Point[4];

for(int i =0; i<4; i++)

{

signX = (i + 1) * xSpan + 10;

signY = pbShow.Height - TranslateY - (int)(seasonValue[i] / 10 * perScaleValue);

pointSign[i] = new Point(signX, signY);

//请注意画园时候的Rectangle位置

g.FillEllipse(new SolidBrush(Color.Blue), new Rectangle(signX - 4, signY - 4, 8, 8));

}

//使用红色画折线

Pen penSign = new Pen(Color.Red, 2);

//将四个坐标点连接起来，注意画的是三条线

for (int i = 0; i < 3; i++)

g.DrawLine(penSign, pointSign[i], pointSign[i + 1]);

//标出每个季度

int strX, strY;

for(int i = 0;i<4;i++)

{

strX = (i + 1) * xSpan - 5;

strY = pbShow.Height - TranslateY + 10;

g.DrawString(seasonName[i], new Font("黑体", 10), new SolidBrush(Color.Blue), new Point(strX, strY));

}

//绘制扇形图

private void DrawPie()

{

//标注每个季度

int[] seasonValue = new int[4];

seasonValue[0] = (int)nudSeason1.Value;

seasonValue[1] = (int)nudSeason2.Value;

seasonValue[2] = (int)nudSeason3.Value;

seasonValue[3] = (int)nudSeason4.Value;

string[] seasonName = { "一季度", "二季度", "三季度", "四季度" };

//我们要获得4个季度总的盈利

int seasonSum = 0;

for (int i = 0; i < 4; i++)

seasonSum += seasonValue[i];

//根据总赢利情况，来获得每个季度在饼图中所占的份额（角度）

//为了简化起见，这里直接取整数

int[] seasonAngle = new int[5];

seasonAngle[0] = 0;

seasonAngle[1] = seasonValue[0] * 360 / seasonSum;

seasonAngle[2] = seasonValue[1] * 360 / seasonSum + seasonAngle[1];

seasonAngle[3] = seasonValue[2] * 360 / seasonSum + seasonAngle[2];

seasonAngle[4] = 360;

//分别用4种颜色表示不同季度的盈利

System.Drawing.Color[] seasonColor = { Color.Red, Color.Blue, Color.Green, Color.GreenYellow };

for(int i = 0;i<4;i++)

{

g.FillPie(new SolidBrush(seasonColor[i]), new Rectangle(50, 80, 200, 200), seasonAngle[i], seasonAngle[i + 1] - seasonAngle[i]);

//饼图中特别需要说明每个季度对应的颜色

g.FillRectangle(new SolidBrush(seasonColor[i]), new Rectangle(260, i * 30 + 20, 30, 20));

//标出每个季度

g.DrawString(seasonName[i], new Font("宋体", 12), new SolidBrush(Color.Black), new Point(300, i * 30 + 20));

}

//绘制环形图

private void DrawAnnular()

{

//标注每个季度

int[] seasonValue = new int[4];

seasonValue[0] = (int)nudSeason1.Value;

seasonValue[1] = (int)nudSeason2.Value;

seasonValue[2] = (int)nudSeason3.Value;

seasonValue[3] = (int)nudSeason4.Value;

string[] seasonName = { "一季度", "二季度", "三季度", "四季度" };

//我们要获得4个季度总的盈利

int seasonSum = 0;

for (int i = 0; i < 4; i++)

seasonSum += seasonValue[i];

//根据总赢利情况，来获得每个季度在饼图中所占的份额（角度）

//为了简化起见，这里直接取整数

int[] seasonAngle = new int[5];

seasonAngle[0] = 0;

seasonAngle[1] = seasonValue[0] * 360 / seasonSum;

seasonAngle[2] = seasonValue[1] * 360 / seasonSum + seasonAngle[1];

seasonAngle[3] = seasonValue[2] * 360 / seasonSum + seasonAngle[2];

seasonAngle[4] = 360;

//圆环内弧与外弧之间的距离

int xSpace = 50;

//分别用4种颜色表示不同季度的盈利

Color[] seasonColor = { Color.Red, Color.Blue, Color.Green, Color.GreenYellow };

//这里使用GraphicsPath和Region

for(int i=0; i<4;i++)

{

//大的扇形

GraphicsPath pathPieMax = new GraphicsPath();

pathPieMax.AddPie(new Rectangle(50, 80, 200, 200), seasonAngle[i], seasonAngle[i + 1] - seasonAngle[i]);

//小的扇形

GraphicsPath pathPieMin = new GraphicsPath();

pathPieMin.AddPie(new Rectangle(50 + xSpace, 80 + xSpace, 200 - xSpace * 2, 200 - xSpace * 2), seasonAngle[i], seasonAngle[i + 1] - seasonAngle[i]);

//圆环=大的扇形-小的扇形

Region regoinAnnular = new Region(pathPieMax);

regoinAnnular.Exclude(pathPieMin);

//填充区域

g.FillRegion(new SolidBrush(seasonColor[i]), regoinAnnular);

//饼图中特别需要说明每个季度对应的颜色

g.FillRectangle(new SolidBrush(seasonColor[i]), new Rectangle(260, i * 30 + 20, 30, 20));

//标出每个季度

g.DrawString(seasonName[i], new Font("宋体", 12), new SolidBrush(Color.Black), new Point(300, i * 30 + 20));

}

//保存图片

private void btnSave_Click(object sender, EventArgs e)

{

SaveFileDialog sfd = new SaveFileDialog();

sfd.Filter = "JPG文件|*.jpg";

if (sfd.ShowDialog() != DialogResult.OK)

return;

string filename = sfd.FileName;

bmp.Save(filename);

}

运行结果如下图所示：

图17-34 生成环状图

学习更多vb.net知识，请参看vb.net 教程目录

学习更多C#知识，请参看C#教程目录