实例化内容解析器时出现空指针异常？

Question

在我的 Android 中，我正在使用内容解析器读取联系人。但内容解析器没有被初始化，它给出了NullPointerException。 我想在另一个类中使用字符串数组并在其中获取值我必须查询数据库并从手机中读取联系人，但正如代码中指出的那样，遇到了该异常：

//this code is in some other class...     
et= (EditText) findViewById(R.id.searchcontact);
        et.addTextChangedListener(new TextWatcher() {

             public void onTextChanged(CharSequence s, int start, int before, int
             count) { // TODO Auto-generated method stub
                 lva.getFilter().filter(s);

RefreshListView rlv=new RefreshListView();<----class is getting called from here
                 lva.notifyDataSetInvalidated();
                 lva = new ListViewAdapterContacts(AllContactsActivity.this, rlv.names, rlv.types, rlv.phones, rlv.ids);

                 lv.setAdapter(lva);


             }

             public void beforeTextChanged(CharSequence s, int start, int count,
             int after) { // TODO Auto-generated method stub

             }

             public void afterTextChanged(Editable s) { 
                 // TODO Auto-generated  method stub


            // lva.notifyDataSetChanged();
             }
             });

...............********.........

public class RefreshListView extends ListActivity{

            String[] names,phones,types,ids;
            String name,id,phoneNumber;
            int type;
            ArrayList <String> newValues;

        public void onCreate(Bundle b){
        super.onCreate(b);

        newValues=SetNewList.getNames();
        getContacts();
    }



public void getContacts(){
                int foo = 0;


    ContentResolver cr = getContentResolver();<---//null pointer exception

    Cursor cur = cr.query(ContactsContract.Contacts.CONTENT_URI, null,
                        null, null, "UPPER(" + ContactsContract.Contacts.DISPLAY_NAME
                        + ") ASC");
                if (cur.getCount() > 0) {

                    names = new String[cur.getCount()];
                    phones = new String[cur.getCount()];
                    types = new String[cur.getCount()];
                    ids = new String[cur.getCount()];

                    while (cur.moveToNext()) {

                        name = cur
                        .getString(cur
                                .getColumnIndex(ContactsContract.Contacts.DISPLAY_NAME));
                        for(int i=0;i<=newValues.size();i++){           
                            if(newValues.get(i).equalsIgnoreCase(name)) {
                                id = cur.getString(cur
                                        .getColumnIndex(ContactsContract.Contacts._ID));
                                String hasPhone = cur
                                .getString(cur
                                        .getColumnIndex(ContactsContract.Contacts.HAS_PHONE_NUMBER));

                                if (Integer.parseInt(hasPhone) == 1) {

                                    Cursor phones = getContentResolver().query(
                                            ContactsContract.CommonDataKinds.Phone.CONTENT_URI,
                                            null,
                                            ContactsContract.CommonDataKinds.Phone.CONTACT_ID
                                            + " = " + id, null, null);

                                    while (phones.moveToNext()) {
                                        phoneNumber = phones
                                        .getString(phones
                                                .getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));

                                        type = phones.getInt(phones.getColumnIndex(Phone.TYPE));

                                    } // while

                                    phones.close();
                                }// if

                                else {
                                    phoneNumber = "unknown";
                                    type = 0;

                                }// else



                                phones[foo] = phoneNumber;
                                names[foo] = name;
                                ids[foo] = id;

                                if (type == 0) {
                                    String value = "unknown";
                                    types[foo] = value;
                                }

                                else if (type == 1) {
                                    String value = "home";
                                    types[foo] = value;
                                }// if

                                else if (type == 2) {
                                    String value = "mobile";
                                    types[foo] = value;
                                }// else if

                                else if (type == 3) {
                                    String value = "Work";
                                    types[foo] = value;
                                }

                                else if (type == 4) {
                                    String value = "Workfax";
                                    types[foo] = value;
                                }

                                else if (type == 5) {
                                    String value = "Home Fax";
                                    types[foo] = value;

                                } else if (type == 6) {
                                    String value = "Pager";
                                    types[foo] = value;
                                }

                                else {
                                    String value = "Other";

                                    types[foo] = value;
                                }

                                foo++;
                            }
                        }
                    }// while
                }// if


            }// get contacts

        }

Answer 1

别这样……

public class RefreshListView extends ListActivity{

    public RefreshListView() {

        ...

    }
}

不要为 Android Activity 使用构造函数！！！

您应该删除该构造函数并将代码放入 Activity onCreate(...) 方法中。

请参阅Activity 的文档并阅读Activities。

试试这样的...

public class RefreshListView extends ListActivity{

    String[] names,phones,types,ids;
    String name,id,phoneNumber;
    int type;
    ArrayList <String> newValues;
    ContentResolver cr = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        cr = getContentResolver();
        newValues=SetNewList.getNames();//getnames is of static type
        getContacts();
    }

    public void getContacts() {
        int foo = 0;

        // REMOVE THE NEXT LINE !!!
        // ContentResolver cr = getContentResolver();

        ...

    }
}

Answer 2

getContentResolver() 应该在 Activity 的实现中调用 - 尝试覆盖 onCreate()。如果您在活动中将其称为 this.getContentResolver() 会更清楚 = 更易于阅读。

查看this example code（在“绑定到数据”部分之后）。

您可以在所有其他应用程序组件中使用 ContentResolver，您只需要一个 Context。对于 Activity，您会自动使用 Activity 的上下文。您也可以使用Application Context - 它们的生命周期基本上不同。