Iphone 从plist中选择唯一随机字典

我正在开发一个函数，它允许我从一个.plist中选择一个随机字典，它可以显示一个2字符串的问答，效果很好。但是，有时会选择相同的词典。随机函数是否可以每次显示一个唯一的字典？谢谢

plist：

<dict>
<key>questions</key>
<array>
    <dict>
        <key>question</key>
        <string>q1</string>
        <key>answer</key>
        <string>a1</string>
    </dict>
    <dict>
        <key>question</key>
        <string>q2</string>
        <key>answer</key>
        <string>a2</string>
    </dict>
    <dict>
        <key>question</key>
        <string>q3</string>
        <key>answer</key>
        <string>a3</string>
    </dict>
</array>

---

如果不想两次显示同一词典，请执行以下操作之一：

• 跟踪您显示的词典。如果再次选择一个，请重试
• 选择词典时，请将其从选项数组中删除

---

您是否知道我尝试过的removeLastObject:array和RemoveObjectAtIndex:questionIndex的语法，但都不起作用

    NSString *path = [[NSBundle mainBundle] pathForResource:@"qs" ofType:@"plist"];
    NSMutableDictionary *dict = [[NSMutableDictionary alloc] initWithContentsOfFile:path];

    NSMutableArray *array = [dict objectForKey:@"questions"];

    int questionIndex = arc4random() %[array count];

    NSDictionary *question = [array objectAtIndex:questionIndex];
    NSString *answerStr = [question objectForKey:@"answer"];
    NSString *questionStr = [question objectForKey:@"question"];

    label1.text = answerStr;
    label2.text = questionStr;