public String listToString(ArrayList<String> stringList){
    if (stringList == null) {
        return null;
}
    StringBuilder result=new StringBuilder();
    boolean flag=false;
    for (String string : stringList) {
        if (flag) {
            result.append(","); // 分隔符
}else {
            flag=true;
 
}
        result.append(string);
}
    return result.toString();
}

應用場景：

String s1 = listToString(leaders);

tv_duty_new.setText(s1);