java学习之contentprovider

今天我们来谈谈4大组件之一的contentprovier，在android里面数据Shared Preferences、网络存储、文件存储、外储存储、SQLite这5中储存方式，但是如果要用到程序间的数据共享，就要用到contentprovider了，contentprovider主要是通过配置文件申明这个数据可以读取，然后通过contentresolver和contentprovider建立连接，contentprovider里面的uri有具体的格式，如:content://com.jk.contentproviderdemo.MyProvider/person,第一个部分是固定的，第二个包名，，第三个表名，也就是数据库的名字，可能还有一些细节没有说到，但是大概的话应该就是这个样子，如果有需要补充的会在后面更新

package com.jk.contentproviderdemo.dao;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;

public class PersonSQLiteOpenHelper extends SQLiteOpenHelper {
public static String DATABASENANE = "person.db";

public PersonSQLiteOpenHelper(Context context) {
// create a database named person.db
super(context, DATABASENANE, null, 1);

}

@Override
public void onCreate(SQLiteDatabase db) {
// create a table that contain _id,name,number
db.execSQL("create table person (_id integer primary key autoincrement , name text , number text)");

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}

}

package com.jk.contentproviderdemo;

import com.jk.contentproviderdemo.dao.PersonSQLiteOpenHelper;

import android.content.ContentProvider;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;

public class MyProvider extends ContentProvider {

// override the delete method
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
System.out.println("delete");
return 0;
}

// override the get type method
@Override
public String getType(Uri uri) {
System.out.println("get type");
return null;
}

// override the insert method
@Override
public Uri insert(Uri uri, ContentValues values) {
System.out.println("insert");
return null;
}

// override the onCreate method
@Override
public boolean onCreate() {
System.out.println("oncreate");
return false;
}

// override the query method
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
System.out.println("query");

// get a databasehelper class object
PersonSQLiteOpenHelper per = new PersonSQLiteOpenHelper(getContext());
// get a writable object
SQLiteDatabase db = per.getWritableDatabase();
// begin to query and get a Cursor
Cursor c = db.query("person", projection, selection, selectionArgs,
null, null, null);
return c;

}

// override the update method
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
System.out.println("updata");
return 0;
}

}

package com.jk.contentproviderdemo;

import com.jk.contentproviderdemo.dao.PersonSQLiteOpenHelper;

import android.os.Bundle;
import android.app.Activity;
import android.content.ContentValues;
import android.database.sqlite.SQLiteDatabase;
import android.view.Menu;

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

// insert a data
init();

}

private void init() {
// PersonSQLiteOpenHelper per=new PersonSQLiteOpenHelper(this);
// SQLiteDatabase db=per.getWritableDatabase();
// ContentValues contentvalues=new ContentValues();
// contentvalues.put("name", "ni");
// contentvalues.put("number", "1413");
// db.insert("person", null, contentvalues);
}

}

权限：

<provider android:name="com.jk.contentproviderdemo.MyProvider"
android:authorities="com.jk.contentproviderdemo.MyProvider"
android:exported="true"></provider>
</application>

第二个应用程序

package com.example.contentproviderdemotest;

import android.net.Uri;
import android.os.Bundle;
import android.app.Activity;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.database.Cursor;
import android.view.Menu;

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ContentResolver cr = this.getContentResolver();
// init uri
Uri myUri = Uri
.parse("content://com.jk.contentproviderdemo.MyProvider/person");

// get a object that can save data
ContentValues cv = new ContentValues();
// call the insert method that belong to uri
cr.insert(myUri, cv);

// call the query method that belong to uri
Cursor c = cr.query(myUri, null, null, null, null);
// show the data
while (c.moveToNext()) {
int id = c.getInt(c.getColumnIndex("_id"));
String name = c.getString(1);
String number = c.getString(2);
System.out.println(id + name + number);
}
}

}