ArrayList检查数据是否已存在

Just want to check if data already exist(s) or not in ArrayList, but everytime getting : Not Exist(s) whereas data exists in ArrayList, and as a result i am getting duplicate records in a list..

只想检查数据是否已存在于ArrayList中,但每次都得到:Not Exist(s)而数据存在于ArrayList中,因此我在列表中获得重复记录。

    DataArrayList.secondArraylist.add(new Second(actorList.get(position).getName(), actorList.get(position).getImage()));
             System.out.println(DataArrayList.secondArraylist.size());   

             String strName = actorList.get(position).getName().toString();
             Log.d("name:", strName);

             for(int i=0; i<DataArrayList.secondArraylist.size(); i++) 
             {

                 if(DataArrayList.secondArraylist.get(i).getName().equals(strName)) {
                     System.out.println(DataArrayList.secondArraylist.get(i).getName());

                     Toast.makeText(context, "Exist(s)", Toast.LENGTH_SHORT);
                }
                 else {

                     Toast.makeText(context, "Not Exist(s)", Toast.LENGTH_SHORT);
                }

             }

Problem:

Not getting any Toast message, which i am using to indicate that "Data Exists" or "Not"

没有得到任何Toast消息,我用它来表示“数据存在”或“不存在”

Finally:

I would like to add item to arraylist if already not exist(s), else want to show Toast that item already exist(s)

我想将项目添加到arraylist如果已经不存在,否则想要显示Toast该项目已经存在(s)

4 个解决方案

#1

You are comparing your list object DataArrayList.secondArraylist with a String

您正在将列表对象DataArrayList.secondArraylist与String进行比较

if (DataArrayList.secondArraylist.equals(strName)) {

That will always return false. Instead, create a method that loops through the list and checks the strName against the name of the Second objects that are stored in the list.

那将永远是假的。而是创建一个循环遍历列表的方法,并根据列表中存储的第二个对象的名称检查strName。

boolean contains(ArrayList<Second> list, String name) {
    for (Second item : list) {
        if (item.getName().equals(name)) {
            return true;
        }
    }
    return false;
}

Then use it

然后使用它

if (contains(DataArrayList.secondArraylist, strName)) {
    System.out.println("Data Exist(s)");
} else {
    System.out.println("Not Exist(s)");
}

#2

The contains method calls the equals method with signature equals(Object), so you requires to override this method in your POJO class.

contains方法使用签名equals(Object)调用equals方法,因此您需要在POJO类中重写此方法。

If you override equals(Object) then you should also override hashcode()

如果你重写equals(Object),那么你也应该覆盖hashcode()

Code snippet :

代码段:

@Override
public String toString() {
    return getName();
}

 @Override
 public boolean equals(Object obj) {
     return !super.equals(obj);
 }

 @Override
 public int hashCode() {
      return getName().hashCode();
 }

Edit :

Moreover, The contains method is used for Object. So, your condition should look like this :

而且,contains方法用于Object。所以,你的情况应该是这样的:

 (DataArrayList.secondArraylist.contains(actorList.get(position))) 

Final code :

最终代码:

if (DataArrayList.secondArraylist.contains(actorList.get(position))) {
    System.out.println("Data Exist(s)");
} else {
    System.out.println("Not Exist(s)");
}

#3

You need to use indexOf() while checking a value in ArrayList

您需要在检查ArrayList中的值时使用indexOf()

if (DataArrayList.secondArraylist.indexOf(strName)!=-1) {
System.out.println("Data Exist(s)");
    } else {
System.out.println("Not Exist(s)");
}

#4

As the strName you are checking is a property of your Object Second, you cannot check it directly using method of the ArrayList. The easiest way would be loop through the ArrayList DataArrayList.secondArraylist, get each Second object contained in the list, then check if strName is equal to that property of your Second object.

由于您要检查的strName是Object Second的属性,因此无法使用ArrayList的方法直接检查它。最简单的方法是遍历ArrayList DataArrayList.secondArraylist,获取列表中包含的每个Second对象,然后检查strName是否等于Second对象的该属性。

Not sure how you implement the Second object, but you should get the corresponding String from each Second object then compare it with the strName.

不确定如何实现Second对象,但是你应该从每个Second对象获取相应的String,然后将它与strName进行比较。