控制PyQt4 QFileDialog

Question

此代码创建一个带有按钮的窗口，显示Windows QFileDialog：

import java.util.Scanner;
import java.lang.Thread;
class Hello{  
public static void main(String[] args){  
try{
    long count =0;
 for(;;){
     A a = new A();
     count++;

     if(count%100 ==0)
     System.out.println("Created "+ count);

 }
}
catch(Exception ex){
    System.out.println("Exception occured");
    System.out.println(ex);
}}
}

class A{
int a = 10;
String str = generateRandom();
String str1 = generateRandom();
String str2 = generateRandom();
String str3 = generateRandom();
String str4 = generateRandom();
String str5 = generateRandom();
String str6 = generateRandom();
String str7 = generateRandom();
String str8 = generateRandom();
String str9 = generateRandom();
String str10 = generateRandom();
String rst1 = generateRandom();
String rst2 = generateRandom();
String rst3 = generateRandom();
String rst4 = generateRandom();
String rst5 = generateRandom();
String rst6 = generateRandom();
String rst7 = generateRandom();
String rst8 = generateRandom();
String rst9 = generateRandom();
String rst10 = generateRandom();



private static String generateRandom() {
    String aToZ = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
Random rand=new Random();
StringBuilder res=new StringBuilder();
for (int i = 0; i < 17; i++) {
   int randIndex=rand.nextInt(aToZ.length()); 
   res.append(aToZ.charAt(randIndex));            
}
return res.toString();

有一个问题。当我打开QFileDialog并关闭它而不选择文件时，QLineEdit中的字符串将被删除。但我希望它留下来。我该怎么做？