ArrayList的空指针异常 [英] ArrayList null pointer exception

问题描述

我已经创建了一个ArrayList和一个ListView。我打算通过ListView的迭代，并检查他们是否被选中与否，然后添加对象（使用ListView.getItem（）），以我的数组列表。但是，我得到一个NullPointerException异常。 people_selected ArrayList中，在这样的类顶部声明：

 的ArrayList＆LT; PeopleDetails＆GT; selected_people;
 

和我的code：

 的for（int i = 0; I＆LT; people_list.getCount（）;我++）{
              item_view = people_list.getAdapter（）getView（I，NULL，NULL）;
                chBox =（复选框）item_view.findViewById（R.id.checkBox）; //你的XML值复选框ID。
                如果（chBox.isChecked（））{
                    selected_people.add（（PeopleDetails）people_list.getItemAtPosition（一））;
                }
            }        对于（PeopleDetails人：selected_people）{            SmsManager短信= SmsManager.getDefault（）;
            sms.sendTextMessage（person.number，空，sms_message，NULL，NULL）;
            }
        ///现在需要编写方文件。
 

我在该行得到一个错误

  

有关（PeopleDetails人：selected_people）

说NullPointerException异常
。我认为这意味着该ArrayList是空的，不能弄清楚为什么它应该为null。难道我宣布它错在我班上的第一名？或者是我的选择和添加方法有问题？

感谢您的帮助！ ：）

解决方案

 的ArrayList＆LT; PeopleDetails＆GT; people_selected;
 

您声明并永远不会初始化。在使用它之前只是初始化。否则 NullPointerException异常。

尝试初始化它

 的ArrayList＆LT; PeopleDetails＆GT; people_selected =新的ArrayList＆LT; PeopleDetails＆GT;（）;
 

I have created an arraylist, and a ListView. I intend to iterate through the ListView, and checking whether they are checked or not, and then add the object (using ListView.getItem()) to my arraylist. however I get a NullPointerException. The ArrayList people_selected, is declared at top of class like this:

ArrayList<PeopleDetails> selected_people;

And my code:

for (int i = 0; i < people_list.getCount(); i++) {
              item_view = people_list.getAdapter().getView(i, null, null);
                chBox = (CheckBox) item_view.findViewById(R.id.checkBox);//your xml id value for checkBox.
                if (chBox.isChecked()) {
                    selected_people.add((PeopleDetails) people_list.getItemAtPosition(i));
                }
            }

        for(PeopleDetails person : selected_people){

            SmsManager sms = SmsManager.getDefault();
            sms.sendTextMessage(person.number, null, sms_message, null, null);        
            }
        ///and now need to write party to file.

I get an error at the line

for(PeopleDetails person : selected_people)

Saying "NullPointerException" . I take this to mean that the arraylist is null, and cannot figure out why it should be null. Have I declared it wrong at the top of my class? Or is my selection and add method faulty?

Thanks for the help!! :)

解决方案

ArrayList<PeopleDetails> people_selected;

You declared and never initialized. Just initialize it before using it. Otherwise NullPointerException.

Try to initialize it

ArrayList<PeopleDetails> people_selected= new ArrayList<PeopleDetails>();

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