Android四大组件之ContentProvider

ContentProvider主要是提供了我们访问数据的统一接口，一旦一个类继承了ContengProvider,我们就会称这个应用程序为ContengProvider(内容提供者)

使用ContentProvider的步骤：

1、写一个类继承ContentProvider,并改写其中的一些方法。

2、在AndroidManifest.xml文件中声明你所定义的provider

 

在使用ContentProvider之前先要了解两个类的使用：

UriMatcher:

UriMatcher类用于匹配Uri，它的用法如下：

首先第一步把你需要匹配Uri路径全部给注册上，如下：

// 常量 UriMatcher.NO_MATCH 表示不匹配任何路径的返回码

UriMatcher  sMatcher = new UriMatcher(UriMatcher.NO_MATCH);

// 如果 match() 方法匹配 content://cn.itcast.provider.personprovider/person 路径，返回匹配码为 1

sMatcher.addURI( “ cn.itcast.provider.personprovider ” , “ person ” , 1);// 添加需要匹配 uri ，如果匹配就会返回匹配码

// 如果 match() 方法匹配 content://cn.itcast.provider.personprovider/person/230 路径，返回匹配码为 2

sMatcher.addURI(“cn.itcast.provider.personprovider”, “person/#”, 2); //# 号为通配符

 

ContentUris:

ContentUris类用于获取Uri路径后面的ID部分，它有两个比较实用的方法：

withAppendedId(uri, id)用于为路径加上ID部分：

Uri uri = Uri.parse("content://cn.itcast.provider.personprovider/person")

Uri resultUri = ContentUris.withAppendedId(uri, 10);

// 生成后的 Uri 为： content://cn.itcast.provid

er.personprovider/person/10

parseId(uri)方法用于从路径中获取ID部分：

Uri uri = Uri.parse("content://cn.itcast.provider.personprovider/person/10")

long personid = ContentUris.parseId(uri);// 获取的结果为 :10

 

下面开始使用ContentProvider:

1、定义一个类，继承SQLiteOpenHelper

public class MyDBHelper extends SQLiteOpenHelper
{
	public static final int VERSION=1;
	public static final String DB_NAME="gjun";

	public MyDBHelper(Context context)
	{
		super(context, DB_NAME, null, VERSION);
		// TODO Auto-generated constructor stub
	}

	@Override
	public void onCreate(SQLiteDatabase db)
	{
		// TODO Auto-generated method stub
		
		//通常在此创建数据库中的表
		db.execSQL("create table student(id integer primary key autoincrement,name varchar(20))");
	}

	@Override
	public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
	{
		// TODO Auto-generated method stub

	}

}

2、定义一个类，继承了ContentProvider

public class MyProvider extends ContentProvider
{
	private MyDBHelper helper;
	private SQLiteDatabase db;
	private static final String AUTHORI="com.provider.db.myprovider";
	private static final int ITEM=1;
	private static final int ITEMS=2;
	private static	 final String CONTENT_URI="content://com.provider.db.myprovider";
	
	private static final UriMatcher matcher;
	static
	{
		matcher=new UriMatcher(UriMatcher.NO_MATCH);
		matcher.addURI(AUTHORI,"student",ITEMS);
		matcher.addURI(AUTHORI,"student/#",ITEM);
	}
	
	@Override
	public int delete(Uri uri, String selection, String[] selectionArgs)
	{
		// TODO Auto-generated method stub
		switch(matcher.match(uri))
		{
		case ITEM:
			int num=0;
			StringBuilder sb=new StringBuilder();
			long id=ContentUris.parseId(uri);
			sb.append("id="+id);
			db=helper.getWritableDatabase();
			
			if(selection!=null && !selection.equals(""))
			{
				sb.append(" and selection");
			}
			num=db.delete("student",sb.toString(),selectionArgs);
			return num;
		case ITEMS:
			db=helper.getWritableDatabase();
			num=db.delete("student", selection,selectionArgs);
			return num;
			default:
			throw new IllegalArgumentException("UnKnow Uri:"+uri.toString());	
		}
		
	}

	@Override
	public String getType(Uri uri)
	{
		// TODO Auto-generated method stub
		switch(matcher.match(uri))
		{
		case ITEM:
			return "vnd.android.cursor.item/student";
			
		case ITEMS:
			return "vnd.android.cursor.dir/student";
			
		default:
		throw new IllegalArgumentException("UnKnow URI:"+uri.toString());	
		}
		
	}

	@Override
	public Uri insert(Uri uri, ContentValues values)
	{
		// TODO Auto-generated method stub
		long id=0;
		Uri result=null;
		switch(matcher.match(uri))
		{
		
		
		case ITEM:
			db=helper.getWritableDatabase();
			id=db.insert("student", null, values);
			result=Uri.parse(uri.toString().substring(0, uri.toString().lastIndexOf("/")+1));
			ContentUris.withAppendedId(result, id);
			return result;
		
		case ITEMS:	
			db=helper.getWritableDatabase();
			id=db.insert("student", null, values);
			result=ContentUris.withAppendedId(uri, id);
			
			return result;
		default:
			throw new IllegalArgumentException("UnKnow URI:"+uri.toString());
		}
		
	}

	@Override
	public boolean onCreate()
	{
		// TODO Auto-generated method stub
		helper=new MyDBHelper(this.getContext());
		return true;
	}

	@Override
	public Cursor query(Uri uri, String[] projection, String selection,
			String[] selectionArgs, String sortOrder)
	{
		// TODO Auto-generated method stub
		db=helper.getReadableDatabase();
		Cursor cursor=null;
		switch(matcher.match(uri))
		{
		case ITEM:
			StringBuilder sb=new StringBuilder();
			long id=ContentUris.parseId(uri);
			sb.append("id="+id);
			if(selection!=null && selection.equals(""))
			{
				sb.append("and selection");
			}
			cursor=db.query("student", projection, sb.toString(), selectionArgs,null, null,sortOrder);
			return cursor;
			
		case ITEMS:
			return db.query("student", projection, selection, selectionArgs, null, null, sortOrder);
		default:
			throw new IllegalArgumentException("UnKnow URI:"+uri.toString());
		}
		
	}

	@Override
	public int update(Uri uri, ContentValues values, String selection,
			String[] selectionArgs)
	{
		// TODO Auto-generated method stub
		db=helper.getWritableDatabase();
		int num=0;
		switch(matcher.match(uri))
		{
		case ITEM:
			StringBuilder sb=new StringBuilder();
			long id=ContentUris.parseId(uri);
			sb.append("id="+id);
			if(selection!=null && selection.equals(""))
			{
				sb.append("and selection");
			}
			num=db.update("student", values, sb.toString(), selectionArgs);
			return num;
		case ITEMS:
			num=db.update("student", values, selection, selectionArgs);
			return num;
		default:
			throw new IllegalArgumentException("UnKnow URI:"+uri.toString());
		}
		
	}

}

3、编写一个测试类

public class MainActivity extends Activity implements OnClickListener
{
    /** Called when the activity is first created. */
	
	private Button btnadd=null;
	private Button btnadds=null;
	private Button btndel=null;
	private Button btndels=null;
	private Button btnupdate=null;
	private Button btnupdates=null;
	private Button btnfind=null;
	private Button btnfinds=null;
	
	private ContentResolver resolver=null;
	private Uri uri=Uri.parse("content://com.provider.db.myprovider/student");
	
	
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        init();
        initListener();
        resolver=this.getContentResolver();
    }
    
    public void init()
    {
    	btnadd=(Button)this.findViewById(R.id.btnadd);
    	btnadds=(Button)this.findViewById(R.id.btnadds);
    	btndel=(Button)this.findViewById(R.id.btndel);
    	btndels=(Button)this.findViewById(R.id.btndels);
    	btnupdate=(Button)this.findViewById(R.id.btnupdate);
    	btnupdates=(Button)this.findViewById(R.id.btnupdates);
    	btnfind=(Button)this.findViewById(R.id.btnfind);
    	btnfinds=(Button)this.findViewById(R.id.btnfinds);
    	
    }
    
    public void initListener()
    {
    	btnadd.setOnClickListener(this);
    	btnadds.setOnClickListener(this);
    	btndel.setOnClickListener(this);
    	btndels.setOnClickListener(this);
    	btnupdate.setOnClickListener(this);
    	btnupdates.setOnClickListener(this);
    	btnfind.setOnClickListener(this);
    	btnfinds.setOnClickListener(this);
    }

	@Override
	public void onClick(View v)
	{
		// TODO Auto-generated method stub
		Uri nowuri=null;
		if(v.getId()==R.id.btnadd)
		{
			nowuri=ContentUris.withAppendedId(uri, 1);
			ContentValues cv=new ContentValues();
			cv.put("name", "gavin");
			
			resolver.insert(nowuri,cv);
			Toast.makeText(this, "添加用戶成功！",Toast.LENGTH_SHORT).show();
		}else if(v.getId()==R.id.btnadds)
		{
			ContentValues cv=new ContentValues();
			cv.put("name", "tom");
			
			resolver.insert(uri,cv);
			Toast.makeText(this, "添加用戶成功！",Toast.LENGTH_SHORT).show();
		}else if(v.getId()==R.id.btndel)
		{
			nowuri=ContentUris.withAppendedId(uri, 1);
			resolver.delete(nowuri, null, null);
			Toast.makeText(this, "刪除單個用戶成功!！",Toast.LENGTH_SHORT).show();
		}else if(v.getId()==R.id.btndels)
		{
			resolver.delete(uri, null, null);
			Toast.makeText(this, "刪除所有用戶成功!！",Toast.LENGTH_SHORT).show();
		}else if(v.getId()==R.id.btnfind)
		{
			nowuri=ContentUris.withAppendedId(uri, 6);
			Cursor cursor=resolver.query(nowuri, null, null, null, null);
			cursor.moveToFirst();
			int id=cursor.getInt(cursor.getColumnIndex("id"));
			String name=cursor.getString(cursor.getColumnIndex("name"));
			Toast.makeText(this, "id"+id+" name"+name,Toast.LENGTH_SHORT).show();
		}else if(v.getId()==R.id.btnfinds)
		{
			Cursor cursor=resolver.query(uri, null, null, null, null);
			cursor.move(2);
			int id=cursor.getInt(cursor.getColumnIndex("id"));
			String name=cursor.getString(cursor.getColumnIndex("name"));
			Toast.makeText(this, "id"+id+" name"+name,Toast.LENGTH_SHORT).show();
		}else if(v.getId()==R.id.btnupdate)
		{
			nowuri=ContentUris.withAppendedId(uri, 6);
			ContentValues cv=new ContentValues();
			cv.put("name", "jack");
			resolver.update(nowuri,cv,null,null);
		}else if(v.getId()==R.id.btnupdates)
		{
			ContentValues cv=new ContentValues();
			cv.put("name", "jack");
			resolver.update(uri,cv,null,null);
		}
		
	}
}