四大组件---ContentResolver

一、 ContentResolver的基本用法

ContentResolver是通过URI来查询ContentProvider中提供的数据。

内容URI标准写法如下：

content://com.example.app.provider/table1

内容URI字符串能清楚的表达出是哪个程序的哪个表。ContentResolver中的增删改查方法接收内容URI。需要把URI字符串解析成URI对象。调用Uri.parse()方法即可解析。

Uri uri = Uri.parse("content://com.example.app.provider/table1")

用URI对象查询表table1表中数据

Cursor cursor = getContentResolver().query(
    uri,
    projection,
    selection,
    selectionArgs,
    sortOrder);

查询完成后返回的仍然是Cursor对象，将数据从crsor对象中逐个读取

if(cursor != null){
    
    while(cursor.moveToNext()){
    
        String column1 = cursor.getString(cursor.getColunmIndex("colunm1"));
        int column2 = cursor.getInt(cursor.getColumnIndex("column2");
    }
    cursor.close();
}

添加

ContentValues values = new ContentValues();
values.put("column1", "text");
valuse.put("column2", 1);
getContentResolver().insert(uri.values);

更新

ContentValues values = new ContentValues();
values.put("column1", "");
getContentResolver().update(uri, values, "column1 = ? and column2 = ?", new String[]{
    "text","1"});

删除

getContentResolver().delete(uri, "column2 = ?", new String[]{
    "1"});

二、 读取系统联系人

首先先创建三个联系人

希望最终读取出的联系人信息能在ListView中显示出来。修改主活动xml文件

新建一个列表

修改主活动代码

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 = (ListView) findViewById(R.id.contacts_view);
        adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, contactsList);
        contactsView.setAdapter(adapter);
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_CONTACTS) != PackageManager.PERMISSION_GRANTED) {
    
            ActivityCompat.requestPermissions(this, new String[]{
    Manifest.permission.READ_CONTACTS}, 1);

        } else {
    
            readContacts();
        }
    }
    private void readContacts() {
    
        Cursor cursor = null;
        try {
    
            cursor = getContentResolver().query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI, null, null, null, null);
            if (cursor != null) {
    
                while (cursor != null) {
    
                    //获取联系人姓名
                    @SuppressLint("Range") String displayName = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
                    @SuppressLint("Range") 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, "u denied the permission", Toast.LENGTH_SHORT).show();
                }
                break;
            default:
        }
    }
}

在AndriodMainfest.xml修改代码

<uses-permission android:name="android.permission.READ_CONTACTS"/>

点击ALLOW,联系人的数据都成功读取出来了，说明跨程序访问数据的功能确实是实现了。