ContentProvider的demo

本文参考自郭霖《第一行代码》第2版。

ContentProvider的用法一般有两种：
1.使用现有的内容提供器来读取和操作相应程序中的数据
2.创建自己的内容提供器给我们程序的数据提供外部访问接口

一、第一种用法的demo:

获取联系人数据，放在一个ListView中，代码如下：

public class MainActivity extends AppCompatActivity {

    ArrayAdapter<String> adapter;
    List<String> contactsList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ListView contactsView = findViewById(R.id.contacts_view);
        adapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, contactsList);
        contactsView.setAdapter(adapter);
        if (checkSelfPermission(Manifest.permission.READ_CONTACTS)
                != PackageManager.PERMISSION_GRANTED) {//如果用户没有授权该权限
            requestPermissions(new String[]{Manifest.permission.READ_CONTACTS}, 1);
        } else {//用户已经授权该权限
            readContacts();
        }
    }

    /**
     * 查询联系人
     */
    private void readContacts() {
        Cursor cursor = null;
        try {
            //查询联系人数据
            cursor = getContentResolver().query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,
                    null, null, null, null);
            if (cursor != null) {
                while (cursor.moveToNext()) {
                    //获取联系人姓名
                    String displayName = cursor.getString
                            (cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
                    //获取联系人手机号
                    String number = cursor.getString
                            (cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));
                    contactsList.add(displayName + "\n" + number);
                }
                adapter.notifyDataSetChanged();
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (cursor != null) {
                cursor.close();
            }
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
//        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        switch (requestCode) {
            case 1:
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    readContacts();
                } else {
                    Toast.makeText(this, "You denied the permission", Toast.LENGTH_SHORT).show();
                }
                break;
            default:
                break;
        }
    }
}