package graphic;
import java.awt.Color;
import java.awt.FontMetrics;
import java.awt.Component;
import java.awt.Graphics;
import java.awt.Insets;
import javax.swing.JTextArea;
import javax.swing.border.AbstractBorder;
public class LineNumberBorder extends AbstractBorder {
public LineNumberBorder(){
}
/*Insets 对象是容器边界的表示形式。
它指定容器必须在其各个边缘留出的空间。
*/
//此方法在实例化时自动调用
//此方法关系到边框是否占用组件的空间
public Insets getBorderInsets(Component c)
{
return getBorderInsets(c,new Insets(0,0,0,0));
}
public Insets getBorderInsets(Component c, Insets insets)
{
if(c instanceof JTextArea){
int width=lineNumberWidth((JTextArea)c);
insets.left=width;
}
return insets;
}
public boolean isBorderOpaque()
{
return false;
}
//边框的绘制方法
//此方法必须实现
public void paintBorder(Component c, Graphics g, int x, int y, int width, int height)
{
//获得当前剪贴区域的边界矩形。
java.awt.Rectangle clip=g.getClipBounds();
FontMetrics fm=g.getFontMetrics();
int fontHeight=fm.getHeight();
//starting location at the "top" of the page...
// y is the starting baseline for the font...
int ybaseline=y+fm.getAscent();
// now determine if it is the "top" of the page...or somewhere else
int startingLineNumber=(clip.y/fontHeight)+1;
if(startingLineNumber!=1){
ybaseline=y+startingLineNumber*fontHeight-
(fontHeight-fm.getAscent());
}
int yend=ybaseline+height;
if(yend>(y+height)){
yend=y+height;
}
JTextArea jta=(JTextArea)c;
int lineWidth=lineNumberWidth(jta);
int lnxStart=x+lineWidth;
g.setColor(Color.blue);
// loop until out of the "visible" region...
int length=(""+Math.max(jta.getRows(), jta.getLineCount()+1)).length();
//绘制行号
while(ybaseline<yend)
{
String label = padLabel(startingLineNumber, length, true);
g.drawString(label, lnxStart- fm.stringWidth(label), ybaseline);
ybaseline+=fontHeight;
startingLineNumber++;
}
}
//寻找适合的数字宽度
private int lineNumberWidth(JTextArea jta){
int lineCount=Math.max(jta.getRows(), jta.getLineCount());
return jta.getFontMetrics(jta.getFont()).stringWidth(lineCount+" ");
}
private static String padLabel(int lineNumber, int length, boolean addSpace)
{
StringBuffer buffer=new StringBuffer();
buffer.append(lineNumber);
for(int count=(length-buffer.length());count>0;count--){
buffer.insert(0, ' ');
}
if(addSpace){
buffer.append(' ');
}
return buffer.toString();
}
}
