小程序画多条线时，只显示最后一条 [英] When drawing multiple lines in applet, it shows only the last one
问题描述
我正在尝试使用 Java 小程序和画布绘制多条线.我已经定义了类 Canvas:
I am trying to draw multiple lines by using Java applet and canvas. I have defined class Canvas:
public class Canvas extends JPanel {
private static final int RIGHT=0, LEFT=1, UP=2, DOWN=3;
public static final int WIDTH=600, HEIGHT=500;
private int direction = 0 ;
private int pixels;
/**
* Canvas() constructor sets its size
*/
public Canvas() {
setSize(WIDTH, HEIGHT);
}
public void setPatt(int pat, int lev) {
direction = pat;
pixels = lev;
}
public void paintComponent(Graphics g) {
g.setColor(getForeground());
switch (direction) {
case LEFT:
drawLineLeft(g, pixels);
break;
case RIGHT:
drawLineRight(g, pixels);
break;
case UP:
drawLineUp(g, pixels);
break;
case DOWN:
drawLineDown(g, pixels);
break;
}
}
private void drawLineLeft(Graphics g, int pix){
if(pix > 0){
Dimension d = getSize();
int x = d.width/2;
int y = d.height/2;
g.drawLine(x, y, x-10*pix, y);//left
}
}
private void drawLineUp(Graphics g, int pix){
if(pix > 0){
Dimension d = getSize();
int x = d.width/2;
int y = d.height/2;
g.drawLine(x, y, x, y-10*pix);//up
}
}
private void drawLineRight(Graphics g, int pix){
//Graphics2D g2 = (Graphics2D) g;
if(pix > 0){
Dimension d = getSize();
int x = d.width/2;
int y = d.height/2;
g.drawLine(x, y, x+10*pix, y);//right
}
}
private void drawLineDown(Graphics g, int pix){
if(pix > 0){
Dimension d = getSize();
int x = d.width/2;
int y = d.height/2;
g.drawLine(x, y, x, y+10*pix);// down
}
}
}
我还有另一个类，我在其中定义了下拉列表、文本字段和按钮.我可以从下拉列表中选择应该绘制线条的方向(右、左、上、下 - 方向)，我可以通过在文本字段中输入数字(像素)来定义线条的长度.当按钮被按下时，方法 setPatt 被调用并在画布中出现一行:
I also have another class where I have defined drop down list, text field and button. I can choose direction from drop down list in which line should be painted (RIGHT, LEFT, UP, DOWN - direction) and I can define how long the line will be by typing a number in text field (pixels). When the button is pushed, method setPatt is called and line appears in canvas:
public class TurtleApplet extends JApplet implements ActionListener
{
.....
.....
.....
public void actionPerformed( ActionEvent e)
{
if(e.getSource() == drawButton){
int y = Integer.parseInt(pixels.getText());
canvas.setPatt(direction.getSelectedIndex(), Integer.parseInt(pixels.getText()));
}
//repaint();
}
.....
}
问题是，当我按下按钮时，只有当我调整小程序窗口大小时，画布中才会出现新行.我尝试添加 repaint() 方法，这有帮助，但仍然存在另一个问题 - 如何在不丢失前一行的情况下绘制新线?
The problem is that when I push the button new line appears in canvas only then when I resize applet window. I tried to add repaint() method, this helped, but still there is another problem - how to make draw new line without losing the previous one?
只有最后一行在屏幕上可见，例如，当我从中心向左画一条线(线总是从画布中心开始)然后我想从右边画一条新线居中，第一行消失，我只能看到第二行，依此类推.
Only the last line is visible on the screen, for example, when I draw a line to the left from center (line always starts from the center of canvas) and then I want to draw a new line to the right from the center, the line first line disappears and I can see only the second one and so on.
推荐答案
您应该跟踪已绘制的线条.paintComponent 方法应该打印(或重新打印)整个组件.据我所知，你总是只打印 1 行，因此你失去了以前的状态.
You should keep track of lines drawn already. The paintComponent method supposed to print (or reprint) the entire component. As far as I see you always print just 1 line, therefore you loose the previous state.
尝试创建一个 Map，在其中存储线数据并在 paintComponent 方法中迭代以绘制所有线.
Try to create a Map<Integer, Integer> where you store the line data and iterate through in the paintComponent method to draw all lines.
方法 setPatt 可以改为调用 addPatt.
The method setPatt may be called addPatt instead.
PS:如果顺序很重要，试试LinkedHashMap
PS: If the order matters, try LinkedHashMap
这篇关于小程序画多条线时，只显示最后一条的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
