android - 如何从第二个 Activity 中的第一个 Activity 中获取数组列表的内容

Question

所有任务.java

public class AllTask extends AppCompatActivity{


    ArrayList<Company> companyList;
    Bundle extras;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.task_list);


        companyList=new ArrayList<>();
        companyList.add(new Company("Kony Labs","10:30","Good"));
        companyList.add(new Company("Delloite","12:30","Very Good"));
        companyList.add(new Company("Accenture","14:30","Average"));
        companyList.add(new Company("Microsoft","16:30","Very Good"));
        companyList.add(new Company("TCS","18:30","Good"));


    }
}

AllReports.java

public class AllReports extends AppCompatActivity {

    ArrayList<Company> report_companyList;
    Bundle extras;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_all_reports);


        getSupportActionBar().setTitle("Reports");

        AllTask all_tasks=new AllTask();
        report_companyList=new ArrayList<>(all_tasks.companyList);



        ListView listView = (ListView) findViewById(R.id.report_list);

        MyAdapterResults myAdapter=new MyAdapterResults(this,R.layout.list_view_row_item,report_companyList);
        listView.setAdapter(myAdapter);
    }
}

我想在第二个 Activity 的 ListView 中的第一个 Activity 中的 ArrayList 中显示数据，但是当我试图从第二个 Activity 中的第一个 Activity 中获取数据时，它给出了 NullPointerException ArrayList 是空的。如何在第二个activity中获取ArrayList的内容。

Answer 1

你可以让你的companyList静态

static ArrayList<Company> companyList;

然后这样调用它:

AllTask.companyList

不推荐这种方法。您应该改为在您的 Company 类中实现 Serializable 或 Parcelable 并像这样传递数据:

Bundle bundle = new Bundle();
bundle.putSerializable("data", companyList);
intent.putExtras(bundle);

然后像这样从第二个 Activity 中读取它:

Bundle bundle = getIntent.getExtras();
List<Company> data= (List<Company>)bundle.getSerializable("data");