移动端_IOS【Android基础入门〖6〗】四大组件之ContentProvider
Posted on 2013年09月24日 22:09:38
简介
简而言之,ContentProvider 向别的应用程序提供数据(联系人这个应用程序提供了 它的 ContentProvider),ContentResolver 从别的应用程序(已提供 ContentProvider)获取、修改、添加数据(我们可以通过 ContentResolver 来操纵联系人中的数据)。
说明
既然是四大组件之一,那么创建步骤基本相同
1: 自定义 ContentProvider
2: 注册
3: 使用
1 自定义 ContentProvider
MyProvider.java
package com.myprovider;
import android.content.ContentProvider;
import android.content.ContentUris;
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 {
DatabaseHelper dbhelper;
SQLiteDatabase db;
UriMatcher UMatcher = new UriMatcher(UriMatcher.NO_MATCH);
@Override
public boolean onCreate() {
dbhelper = new DatabaseHelper(getContext(), "michael", null, 1);
UMatcher.addURI("com.michael", "michael", 1);
UMatcher.addURI("com.michael", "michael/#", 2);
db = dbhelper.getWritableDatabase();
return true;
}
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
Cursor cursor;
switch (UMatcher.match(uri)) {
case 1:
cursor = db.query("michael", projection, selection, selectionArgs, null, null, sortOrder);
break;
case 2:
long id = ContentUris.parseId(uri);
String myselection = "_id=" + id;
if (selection != null)
myselection += selection;
cursor = db.query("michael", projection, myselection, selectionArgs, null, null, sortOrder);
break;
default:
throw new IllegalArgumentException("unknow uri" + uri.toString());
}
return cursor;
}
@Override
public String getType(Uri uri) {
return null;
}
@Override
public Uri insert(Uri uri, ContentValues values) {
long id = db.insert("michael", "username", values);
return ContentUris.withAppendedId(uri, id);
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
int num;
switch (UMatcher.match(uri)) {
case 1:
num = db.delete("michael", selection, selectionArgs);
break;
case 2:
long id = ContentUris.parseId(uri);
String myselection = "_id=" + id;
if (selection != null)
myselection += selection;
num = db.delete("michael", myselection, selectionArgs);
break;
default:
throw new IllegalArgumentException("unknow uri" + uri.toString());
}
return num;
}
@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
int num;
switch (UMatcher.match(uri)) {
case 1:
num = db.update("michael", values, selection, selectionArgs);
break;
case 2:
long id = ContentUris.parseId(uri);
String myselection = "_id=" + id;
if (selection != null)
myselection += selection;
num = db.update("michael", values, myselection, selectionArgs);
break;
default:
throw new IllegalArgumentException("unknow uri" + uri.toString());
}
return num;
}
}
2 封装的 SQLiteOpenHelper 用以操作数据库
DatabaseHelper.java
package com.myprovider;
import android.content.ContentValues;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseHelper extends SQLiteOpenHelper {
public DatabaseHelper(Context context, String name, CursorFactory factory, int version) {
super(context, name, factory, version);
}
@Override
public void onCreate(SQLiteDatabase db) {
//创建数据库
db.execSQL("create table michael(_id integer primary key autoincrement ,username text);");
//初始数据
ContentValues values = new ContentValues();
values.put("username", "张三");
db.insert("michael", "username", values);
values.put("username", "李四");
db.insert("michael", "username", values);
values.put("username", "王五");
db.insert("michael", "username", values);
values.put("username", "赵六");
db.insert("michael", "username", values);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//升级数据库
db.execSQL("drop table if exists michael;");
this.onCreate(db);
}
}
3 注册
AndroidManifest.xml
<provider android:name="com.myprovider.MyProvider" android:authorities="com.michael" android:exported="true" />
4 访问数据 (在别的应用程序中亦同)
意思是,你新建一个项目,具备如下代码,仍然能操作访问 上述项目中的数据 。 这就是 ContentProvider 的神奇之处 :)
4.1 MainActivity.java
package com.myprovider;
import android.app.Activity;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ContentResolver resolver = this.getContentResolver();
Uri uri = Uri.parse("content://com.michael/michael");
ContentValues values = new ContentValues();
values.put("username", "霸王龙");
resolver.insert(uri, values);
values.put("username", "巨无霸");
resolver.insert(uri, values);
values.put("username", "擎天柱");
resolver.insert(uri, values);
values.put("username", "大黄蜂");
resolver.insert(uri, values);
Cursor cursor = resolver.query(uri, new String[]{"_id", "username"}, null, null, null);
SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, android.R.layout.simple_list_item_2, cursor, new String[]{"_id", "username"}, new int[]{android.R.id.text1, android.R.id.text2}, 0);
ListView listview = (ListView) findViewById(R.id.listview);
listview.setAdapter(adapter);
}
}
4.2 activity_main.xml 布局文件
<ListView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/listview"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>