Android ContentProvider 陌生的四大组件之一实现数据共享

小咪咪 2022-07-19 05:12 104阅读 0赞

1. Android 应用程序能够将数据保存到SharedPreference中，也可以保存到文件，SQLite数据库中，甚至任何有效的设备中，但是当你想将你的应用数据与其他的应用共享时，内容提供者就可以发挥作用了。

2. ContentProvider的主要作用：Content provider机制可支持在多个应用中存储和读取数据。这也是跨应用共享数据的唯一方式。在android系统中，没有一个公共的内存区域，供多个应用共享存储数据。

通俗的来说：在Android中，默认使用SQLite作为系统的DB， 但是在Android中，使用方法有点小小的不一样。在Android中每一个应用都运行在各自的进程中，当你的应用需要访问其他应用的数据是，也就需要数据在不同的虚拟机之间传递，这样的情况操作起来可能有些困难。因为在正常情况下，你不能读取其他应用的db文件，ContentProvider正是用来解决在不同应用包之间共享数据的工具。所有被一个Android应用程序创建的偏好设置，文件和数据库都是私有的。为了和其他的应用程序共享数据，应用程序不得不创建一个ContentProvider,去其他的应用程序取数据，他自己的Content Provider必须被调用。Android 本地的Content Provider包括：

CallLog : 地址和接收到的电话信息

Contact.People.Phone : 存储电话号码

Setting.System : 系统设置和偏好设置

Content Provider所提供的函数：

query()  insert()  update()  delete()  getType()  onCreate()等

下面给出一个例子，让大家更好的了解Content Provider

增删改查实例：

1.创建person库，person表

public class DBOpenHelper extends SQLiteOpenHelper{
        private static final String DATABASE_NAME="person.db"; //数据库名称
        private static final int DATABASE_VERSION =1; //数据库的版本
        public DBOpenHelper(Context context){
             super(context,DATABASE_NAME, null, DATABASE_VERSION);
         }
          @Override
           public void onCreate(SQLiteDatabase db){
                db.execSQL("CREATE TABLE person (_id integer primary key autoincrement, name varchar(20), age varchar(10))");
           }
           @Override
            public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion){
                db.execSQL("DROP TABLE IF EXISTS Person");
                 onCreate(db);
           }
    }

2. 自定义Content Provider类，实现增删改查

public class PersonProvider extends ContentProvider{
      private DBOpenHelper dbOpenHelper;
      private static final UriMatcher MATCHER =new UriMatcher(UriMatcher.NO_MATCH);
      private static final int PERSONS = 1;
      private static final int PERSON = 2;
      static {
         MATCHER.addURI("cn.com.karl.personProvider","person",PERSONS);
         MATCHER.addURI("cn.com.karl.personProvider","person/#",PERSON); 
      }
      @Override
      public boolean onCreate(){
         this.dbOpenHelper = new DBOpenHelper(this.getContext());
         return false;
      }
      @Override
      public Cursor query(Uri uri, String[] projection,String selection,String[] selectionArgs,String sortOrder){
         SQLiteDatabase db= dbOpenHelper.getReadableDatabase();
         switch(MATCHER.match(uri)){
            case PERSONS: //查询所有的时候
    	     return db.query("person",projection,selection,selectionArgs,null,null,sortOrder);
    	case PERSON: //查询某一id的人的信息
    	     long id=ContentUris.parseId(uri);
    	     String where= "_id="+id;
    	     if(selection != null && !"".equals(selection)){
    	        where = selection +"and"+ where;
    	     }
    	     return db.query("person",projection,where,selectionArgs,null,null,sortOrder);
    	default:
    	     throw new IllegalArgumentException("UnKwon Uri:"+uri.toString());
         }
      }
      //返回数据的MIME类型
      @Override
      public String getType(Uri uri){
         switch(MATCHER.match(uri)){
             case PERSONS:
    	      return "vnd.android.cursor.dir/person";
    	 case PERSON:
    	      return "vnd.android.cursor.item/person";
    	 default:
    	      throw new IllegalArgumentException("Unkwon Uri:"+uri.toString());
         }
      }
        // 插入person表中的所有记录 /person  
        // 插入person表中指定id的记录 /person/10  
        @Override  
        public Uri insert(Uri uri, ContentValues values) {  
            // TODO Auto-generated method stub  
            SQLiteDatabase db = dbOpenHelper.getWritableDatabase();  
            switch (MATCHER.match(uri)) {  
            case PERSONS:  
                // 特别说一下第二个参数是当name字段为空时，将自动插入一个NULL。  
                long rowid = db.insert("person", "name", values);  
                Uri insertUri = ContentUris.withAppendedId(uri, rowid);// 得到代表新增记录的Uri  
                this.getContext().getContentResolver().notifyChange(uri, null);  
                return insertUri;  
      
            default:  
                throw new IllegalArgumentException("Unkwon Uri:" + uri.toString());  
            }  
        }  
      
        @Override  
        public int delete(Uri uri, String selection, String[] selectionArgs) {  
            // TODO Auto-generated method stub  
            SQLiteDatabase db = dbOpenHelper.getWritableDatabase();  
            int count = 0;  
            switch (MATCHER.match(uri)) {  
            case PERSONS:  
                count = db.delete("person", selection, selectionArgs);  
                return count;  
      
            case PERSON:  
                long id = ContentUris.parseId(uri);  
                String where = "_id=" + id;  
                if (selection != null && !"".equals(selection)) {  
                    where = selection + " and " + where;  
                }  
                count = db.delete("person", where, selectionArgs);  
                return count;  
      
            default:  
                throw new IllegalArgumentException("Unkwon Uri:" + uri.toString());  
            }  
        }  
      
        @Override  
        public int update(Uri uri, ContentValues values, String selection,  
                String[] selectionArgs) {  
            // TODO Auto-generated method stub  
            SQLiteDatabase db = dbOpenHelper.getWritableDatabase();  
            int count = 0;  
            switch (MATCHER.match(uri)) {  
            case PERSONS:  
                count = db.update("person", values, selection, selectionArgs);  
                return count;  
            case PERSON:  
                long id = ContentUris.parseId(uri);  
                String where = "_id=" + id;  
                if (selection != null && !"".equals(selection)) {  
                    where = selection + " and " + where;  
                }  
                count = db.update("person", values, where, selectionArgs);  
                return count;  
            default:  
                throw new IllegalArgumentException("Unkwon Uri:" + uri.toString());  
            }  
        }  
      
    }

3.实现的时候的Activity类

public class ResolverDemoActivity extends Activity {    
        /** Called when the activity is first created. */    
        private SimpleCursorAdapter adapter;    
        private ListView listView;   
        private Button button_insert;  
        private Button button_query;  
        private Button button_query_one;  
        private EditText edittext_query;  
        private Button button_update_one;  
        private EditText edittext_update;  
        private Button button_update;  
        private Button button_delete;  
        private Button button_delete_one;  
        private EditText edittext_delete;  
          
          
          
        @SuppressWarnings("deprecation")  
        @Override    
        public void onCreate(Bundle savedInstanceState) {    
            super.onCreate(savedInstanceState);    
            setContentView(R.layout.main);    
                
            listView=(ListView) this.findViewById(R.id.listView);    
            ContentResolver contentResolver = getContentResolver();    
            Uri selectUri = Uri.parse("content://cn.com.karl.personProvider/person");    
            Cursor cursor=contentResolver.query(selectUri, null, null, null, null);    
            adapter = new SimpleCursorAdapter(this, R.layout.item, cursor,    
                        new String[]{"_id", "name", "age"}, new int[]{R.id.id, R.id.name, R.id.age});    
                listView.setAdapter(adapter);    
                listView.setOnItemClickListener(new OnItemClickListener() {    
                    @Override    
                    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {    
                        ListView lView = (ListView)parent;    
                        Cursor data = (Cursor)lView.getItemAtPosition(position);    
                        int _id = data.getInt(data.getColumnIndex("_id"));    
                        Toast.makeText(ResolverDemoActivity.this, _id+"", 1).show();    
                    }    
                });    
                    
                button_insert = (Button) this.findViewById(R.id.insertbutton);    
                button_insert.setOnClickListener(new OnClickListener() {              
                    @Override    
                    public void onClick(View v) {    
                        ContentResolver contentResolver = getContentResolver();    
                        Uri insertUri = Uri.parse("content://cn.com.karl.personProvider/person");    
                        ContentValues values = new ContentValues();    
                        values.put("name", "wangkuifeng");    
                        values.put("age", 23);    
                        Uri uri = contentResolver.insert(insertUri, values);    
                        Toast.makeText(ResolverDemoActivity.this, "添加完成", 1).show();    
                    }    
                });   
                  
                button_query = (Button)this.findViewById(R.id.querybutton);  
                button_query.setOnClickListener(new OnClickListener() {  
                      
                    @Override  
                    public void onClick(View v) {  
                        // TODO Auto-generated method stub  
                            ContentResolver contentResolver = getContentResolver();    
                            Uri selectUri = Uri.parse("content://cn.com.karl.personProvider/person");    
                              
                            Cursor cursor=contentResolver.query(selectUri, null, null, null, null);  
                            SimpleCursorAdapter adapter= new SimpleCursorAdapter(ResolverDemoActivity.this, R.layout.item, cursor,    
                                    new String[]{"_id", "name", "age"}, new int[]{R.id.id, R.id.name, R.id.age});    
                            listView.setAdapter(adapter);  
                              
                            Toast.makeText(ResolverDemoActivity.this, "查询完成", 1).show();   
                    }  
                });  
                button_query_one = (Button)this.findViewById(R.id.queryonebutton);  
                edittext_query = (EditText)this.findViewById(R.id.queryone_et);  
                button_query_one.setOnClickListener(new OnClickListener() {  
                      
                    @Override  
                    public void onClick(View v) {  
                        // TODO Auto-generated method stub  
                        String num = edittext_query.getText().toString();  
                        ContentResolver contentResolver = getContentResolver();    
                        Uri selectUri = Uri.parse("content://cn.com.karl.personProvider/person"+"/"+num);  
                        Cursor cursor=contentResolver.query(selectUri, null, null, null, null);  
                        SimpleCursorAdapter adapter = new SimpleCursorAdapter(ResolverDemoActivity.this, R.layout.item, cursor,    
                                new String[]{"_id", "name", "age"}, new int[]{R.id.id, R.id.name, R.id.age});    
                        listView.setAdapter(adapter);  
                          
                        Toast.makeText(ResolverDemoActivity.this, "查询完成", 1).show();   
                    }  
                });  
                edittext_update = (EditText)this.findViewById(R.id.update_et);  
                button_update_one = (Button)this.findViewById(R.id.updateonebutton);  
                button_update_one.setOnClickListener(new OnClickListener() {  
                      
                    @Override  
                    public void onClick(View v) {  
                        // TODO Auto-generated method stub  
                        String num = edittext_update.getText().toString();  
                        ContentResolver contentResolver = getContentResolver();    
                        Uri updateUri = Uri.parse("content://cn.com.karl.personProvider/person"+"/"+num);  
                        ContentValues values = new ContentValues();    
                        values.put("name", "superjunjin");    
                        values.put("age", 26);    
                        int count = contentResolver.update(updateUri, values, null, null);  
                         
                          
                        Toast.makeText(ResolverDemoActivity.this, "更新完成", 1).show();   
                    }  
                });  
                  
                button_update = (Button)this.findViewById(R.id.updatebutton);  
                button_update.setOnClickListener(new OnClickListener() {  
                      
                    @Override  
                    public void onClick(View v) {  
                        // TODO Auto-generated method stub  
                        ContentResolver contentResolver = getContentResolver();   
                        Uri updateUri = Uri.parse("content://cn.com.karl.personProvider/person");  
                        ContentValues values = new ContentValues();    
                        values.put("name", "superjunjin");    
                        values.put("age", 26);    
                        int count = contentResolver.update(updateUri, values, null, null);  
                         
                        Toast.makeText(ResolverDemoActivity.this, "更新完成", 1).show();   
                    }  
                });  
                  
                button_delete = (Button)this.findViewById(R.id.deletebutton);  
                button_delete.setOnClickListener(new OnClickListener() {  
                      
                    @Override  
                    public void onClick(View v) {  
                        // TODO Auto-generated method stub  
                        ContentResolver contentResolver = getContentResolver();   
                        Uri deleteUri = Uri.parse("content://cn.com.karl.personProvider/person");  
                        contentResolver.delete(deleteUri, null, null);  
                          
                        Toast.makeText(ResolverDemoActivity.this, "删除完成", 1).show();   
                    }  
                });  
                  
                edittext_delete = (EditText)this.findViewById(R.id.delete_et);  
                button_delete_one = (Button)this.findViewById(R.id.deleteonebutton);  
                button_delete_one.setOnClickListener(new OnClickListener() {  
                      
                    @Override  
                    public void onClick(View v) {  
                        // TODO Auto-generated method stub  
                        String num = edittext_delete.getText().toString();  
                        ContentResolver contentResolver = getContentResolver();    
                        Uri deleteUri = Uri.parse("content://cn.com.karl.personProvider/person"+"/"+num);  
                         
                        contentResolver.delete(deleteUri, null, null);  
                         
                          
                        Toast.makeText(ResolverDemoActivity.this, "删除完成", 1).show();  
                    }  
                });  
                  
        }    
    }