检查列表是不是包含多个值android

Posted 2023-02-23

【中文标题】检查列表是不是包含多个值android

【英文标题】：Check if list contains multiple values android检查列表是否包含多个值android

【发布时间】：2013-02-08 11:15:05

【问题描述】：

我已经搜索到：How to check if a value already exists in the database in android。我遇到的问题是吐司从不显示，并且当输入的值与数据库中已有的值匹配时，数据仍然输入到数据库中。我看过有关使用 UNIQUE 确保数据不重复的帖子，但它不适用于我需要做的事情。我已经尝试过 if (entries.contains(checkDuplicates) == false) 和 if (!entries.equals(checkDuplicates))，也得到了相同的结果。我知道这是我想念或不理解的简单事情。请有人帮助我并为我指明正确的方向吗？

    private void saveState() 

    Calendar calendar = Calendar.getInstance();
    SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
    eventDate = sdf.format(calendar.getTime());

    String date = eventDate;
    String event = eventTitle.getText().toString();
    String empID = fiveAndTwo.getText().toString();

    /**
     * CRUD Operations
     * */
    // Inserting entries to DB

    // Reading all contacts
    Log.d("Reading: ", "Reading all entries..");

    List<EventEntries> entries = db.getAllEntries();

    for (EventEntries ee : entries) 
        String log = "Id: " + ee.getID() + " Date: " + ee.getDate() + " Event Name: " + ee.getEvent() + " Emp ID: " + ee.getempID();

        // Writing entries to log
        Log.d("Entry: ", log);


    

    String checkDuplicates =  date + event + empID;

    if (!entries.contains(checkDuplicates)) 

        Log.d("Insert: ", "Inserting ..");

        db.addEntry(new EventEntries(date, event, empID));
        String logEntry = "Date: " + date + " Event Name: " + event + " Emp ID: " + empID;
        Log.d("Entered to DB:", logEntry);

     else 

        Toast.makeText(this,"Employee has already been scanned for this event.", Toast.LENGTH_SHORT).show();

    

编辑：我让它工作了。这是我所做的：

    private void saveState() 

    Calendar calendar = Calendar.getInstance();
    SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
    eventDate = sdf.format(calendar.getTime());

    String date = eventDate;
    String event = eventTitle.getText().toString();
    String empID = fiveAndTwo.getText().toString();

    /**
     * CRUD Operations
     * */

    // Reading all entries
    Log.d("Reading: ", "Reading all entries..");

    List<EventEntries> entries = db.getAllEntries();

    for (EventEntries ee : entries) 
        String log = "Id: " + ee.getID() + " Date: " + ee.getDate() + " Event Name: " + ee.getEvent() + " Emp ID: " + ee.getempID();

        // Writing entries to log
        Log.d("Entry: ", log);

    

    EventEntries checkDuplicates = new EventEntries(date, event, empID);

    if (!entries.contains(checkDuplicates)) 

        Toast.makeText(this,"Successfully entered.", Toast.LENGTH_SHORT).show();

        // Inserting entries to DB
        Log.d("Insert: ", "Inserting ..");
        db.addEntry(new EventEntries(date, event, empID));
        String logEntry = "Date: " + date + " Event Name: " + event + " Emp ID: " + empID;
        Log.d("Entered to DB:", logEntry);


     else  

        empAlert();

    

这是我添加到 EventEntries 类的内容：

    @Override
public int hashCode() 
    final int prime = 31;
    int result = 1;
    result = prime * result + ((_date == null) ? 0 : _date.hashCode());
    result = prime * result + ((_empID == null) ? 0 : _empID.hashCode());
    result = prime * result + ((_event == null) ? 0 : _event.hashCode());
    return result;


@Override
public boolean equals(Object obj) 
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    EventEntries other = (EventEntries) obj;
    if (_date == null) 
        if (other._date != null)
            return false;
     else if (!_date.equals(other._date))
        return false;
    if (_empID == null) 
        if (other._empID != null)
            return false;
     else if (!_empID.equals(other._empID))
        return false;
    if (_event == null) 
        if (other._event != null)
            return false;
     else if (!_event.equals(other._event))
        return false;
    return true;

【参考方案1】：

entries.contains(checkDuplicates) 总是返回 false，因为 entries 是 EventEntries 对象的列表，而 checkDuplicates 是 String。您应该使用EventEntries 对象作为参数调用entries.contains。

还有一件事：

// assuming entries is not empty
EventEntries first = entries.get(0);
entries.contains(first);  // --> this is TRUE

// create a dupe of "first"
EventEntries firstDupe = new EventEntries(.....);
entries.contains(firstDupe);  // --> in *general* this is FALSE

一般来说，第二种情况是假的。如果在EventEntries 类中覆盖equals 方法，那么first.equals(firstDupe) 将返回true，这可能是真的。只有这样，第二个例子才会返回 true。

这是一个示例实现：

public boolean equals(Object obj) 
    if (obj instanceof EventEntries) 
        EventEntries other = (EventEntries)obj;
        if (date.equals(other.date) && event.equals(other.event)
            && empID == other.empID) 
            return true;
        
    
    return false;

（根据需要进行调整。）

【讨论】：

我尝试了下面的评论但没有成功。我是否需要做一些不同的事情来获取 EventsEntries 对象？

感谢您提供的信息。在你的帮助下我得到了它，我发现 ***.com/questions/4404084/… 也对我有帮助。

【参考方案2】：

替换：

String checkDuplicates = date + event + empID;

与：

EventEntries checkDuplicates = new EventEntries(date, event, empID);

【讨论】：

我试过了，它仍然不能正常工作。它从不承认信息已经存在。更改为这会使日期、事件和 empID 成为 EventEntries 对象，对吗？请原谅我的无知，我对android、java和面向对象编程还是新手。

感谢您的帮助。我结合了你的答案和上面的答案来让它工作。