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安卓中ContentProvider组件的用法 实例讲解Android中ContentProvider组件如何使用

summerpxy 人气:0
想了解实例讲解Android中ContentProvider组件怎样使用的相关内容吗,summerpxy在本文为您仔细讲解安卓中ContentProvider组件的用法的相关知识和一些Code实例,欢迎阅读和指正,我们先划重点:Android,ContentProvider,下面大家一起来学习吧。

ContentProvider基本使用
为了在应用程序之间交换数据,android提供了ContentProvider,ContentProvider是不同应用程序之间进行数据交换的标准API,当一个应用程序需要把自己的数据暴露给其他程序使用时,该应用程序就可以通过提供ContentPRovider来实现,其他应用程序就可以通过ContentResolver来操作ContentProvider暴露的数据。

实现ContentProvider的步骤:

1)编写一个类,继承ContentProvider,并且重写里面的CRUD方法。

2)在androidmanifest.xml文件中注册provider。

在androidmanifest.xml中注册provider需要以下3个属性:

             android:name              provider的实现类。

             android:authorities       provider的uri。

             android:exported          provider是否暴露给其他程序。


ContentResovler操作ContentProvider:

1)获取ContentResolver,getContentResovler()方法来自于ContextWrapper,所以activity和service中都可以使用。

2)调用CURD方法,通过参数url,调用指定的ContentProvider的方法。


下面是一个demo,向contentProvider中插入一条数据,并且返回到listview中。

main.xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  tools:context=".Main" >
 
  <ListView
    android:id="@+id/listview"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />
 
</RelativeLayout>

MySQLiteOpenHelper类

package com.app.dao;
 
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
 
public class MySQLiteOpenHelper extends SQLiteOpenHelper {
 
  public MySQLiteOpenHelper(Context context, String name,
      CursorFactory factory, int version) {
    super(context, name, factory, version);
 
  }
 
  @Override
  public void onCreate(SQLiteDatabase db) {
 
    String create_sql = "create table tb_test(_id integer primary key autoincrement,name,gender,age)";
     
    db.execSQL(create_sql);
  }
 
  @Override
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
 
  }
 
}

MyContentProvider类

package com.app.dao;
 
import android.content.ContentProvider;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
 
public class MyContentProvider extends ContentProvider{
 
  MySQLiteOpenHelper helper=null;
  @Override
  public int delete(Uri arg0, String arg1, String[] arg2) {
     
    return 0;
  }
 
  @Override
  public String getType(Uri arg0) {
    // TODO Auto-generated method stub
    return null;
  }
 
  @Override
  public Uri insert(Uri arg0, ContentValues values) {
     
    String insert_sql="insert into tb_test values(null,'wx','boy',17)";
     
    helper.getReadableDatabase().execSQL(insert_sql);
     
    return null;
  }
 
  @Override
  public boolean onCreate() {
     
    helper=new MySQLiteOpenHelper(this.getContext(),"test.db3",null,1);
     
    return true;
  }
 
  @Override
  public Cursor query(Uri arg0, String[] arg1, String arg2, String[] arg3,
      String arg4) {
     
    String query_sql="select * from tb_test";
     
    Cursor cursor=helper.getReadableDatabase().rawQuery(query_sql, null);
     
    return cursor;
  }
 
  @Override
  public int update(Uri arg0, ContentValues arg1, String arg2, String[] arg3) {
    // TODO Auto-generated method stub
    return 0;
  }
 
}

listview的显示界面show.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="horizontal" >
 
  <TextView
    android:id="@+id/name"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />
 
  <TextView
    android:id="@+id/gender"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginLeft="60dp" />
 
  <TextView
    android:id="@+id/age"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginLeft="60dp" />
 
</LinearLayout>

Main.java

package com.app.main;
 
import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.ContentResolver;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.widget.CursorAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
 
public class Main extends Activity {
 
  ContentResolver resolver = null;
 
  ListView lv = null;
 
  @SuppressLint("NewApi")
  @Override
  protected void onCreate(Bundle savedInstanceState) {
 
    super.onCreate(savedInstanceState);
 
    setContentView(R.layout.main);
 
    lv = (ListView) this.findViewById(R.id.listview);
 
    resolver = this.getContentResolver();
 
    String str = "content://com.app.test.db/";
 
    Uri uri = Uri.parse(str);
 
    resolver.insert(uri, null);
 
    Cursor cursor = resolver.query(uri, null, null, null, null);
 
    SimpleCursorAdapter adapter = new SimpleCursorAdapter(this,
        R.layout.show, cursor,
        new String[] { "name", "gender", "age" }, new int[] {
            R.id.name, R.id.gender, R.id.age },
        CursorAdapter.FLAG_REGISTER_CONTENT_OBSERVER);
 
    lv.setAdapter(adapter);
 
  }
 
}

实现效果:(执行了3次插入后的效果)

2016421160202125.png (720×1280)

ContentProvider的单元测试
ContentProvider是android的四大组件之一,在编写代码的时候最好是加上单元测试,这样可以确定对数据的CRUD的正确。本篇文章主要介绍ContentProvider中两个主要辅助类的使用还有单元测试的在ContentProvider中的使用。

需要用到的两个辅助类:UriMatcher类和ContentUris类。

UriMatcher类:能够对输入的uri参数就行匹配,以确定对什么表执行什么样的操作。

ContentUris类:有些方法需要返回uri,运用此类可以方便的生成uri类。

对于单元测试,个人觉得非常有必要在今后写代码的时候使用,这样可以非常准确的确定代码的正确性。

使用单元测试的步骤:

 1)加入instrumentation,这个部分的代码是固定,也可以完全在ADT提供的向导中导入。

<instrumentation
    android:name="android.test.InstrumentationTestRunner"
    android:targetPackage="com.example.android_contentprovider" >
  </instrumentation>

2)添加<uses-library>,这个部分的代码也是固定的写法。

 <uses-library android:name="android.test.runner" />


好了,必备的知识已经讲完了,现在上代码:

1)生成一个SQLiteDatabase类,这个是必需的类MySQLiteOpenHelper类

package com.app.db;
 
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
 
public class MySQLiteOpenHelper extends SQLiteOpenHelper {
 
  private static String DB_NAME = "test.db3";
  private static int VERSION = 1;
 
  public MySQLiteOpenHelper(Context context) {
    super(context, DB_NAME, null, VERSION);
 
  }
 
  @Override
  public void onCreate(SQLiteDatabase db) {
       //建表语句
    String create_student = "create table student(_id integer primary key autoincrement,name varchar(10),age integer,gender vachar(10))";
     
    db.execSQL(create_student);
       //千万不能执行这句  // db.close();
 
  }
 
  @Override
  public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
 
  }
 
}

 
然后添加我们需要的MyContentProvider类:

package com.app.contentprovider;
 
import com.app.db.MySQLiteOpenHelper;
 
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;
import android.util.Log;
 
public class MyContentProvider extends ContentProvider {
 
  MySQLiteOpenHelper helper = null;
 
  private static UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH);
 
  // 匹配单条记录
  private static final int student = 1;
  // 匹配多条记录
  private static final int students = 2;
 
  static {
    matcher.addURI("com.app.wx", "student/#", student);
 
    matcher.addURI("com.app.wx", "student", students);
  }
 
  @Override
  public int delete(Uri uri, String selection, String[] selectionArgs) {
 
    SQLiteDatabase db = helper.getWritableDatabase();
 
    int action = matcher.match(uri);
 
    switch (action) {
     
    // 匹配单条记录
    case student:
 
      long id = ContentUris.parseId(uri);
     //获取单条记录的id号
      String delete_id = "_id=" + id;
 
      if (selection != null) {
        delete_id += delete_id + " and " + selection;
      }
 
      db.delete("student", delete_id, selectionArgs);
 
      break;
       
    // 匹配多条记录
    case students:
 
      db.delete("student", selection, selectionArgs);
 
      break;
    }
     
    return 0;
  }
 
  //必需实现这个方法,这个方法与intent有关系,以后再讲
  @Override
  public String getType(Uri uri) {
 
    int code = matcher.match(uri);
    switch (code) {
    case student:
      return "vnd.android.cursor.item/student_item";
    case students:
      return "vnd.android.cursor.dir/students";
    default:
      return null;
    }
  }
 
  @Override
  public Uri insert(Uri uri, ContentValues values) {
 
    SQLiteDatabase db = helper.getWritableDatabase();
 
    int action = matcher.match(uri);
 
    switch (action) {
 
    case students:
 
      long id1 = db.insert("student", "_id", values);
 
      Log.i("--------", ContentUris.withAppendedId(uri, id1).toString());
 
      return ContentUris.withAppendedId(uri, id1);
 
    }
 
    return null;
  }
 
  @Override
  public boolean onCreate() {
 
    helper = new MySQLiteOpenHelper(this.getContext());
 
    return true;
  }
 
  @Override
  public Cursor query(Uri uri, String[] projection, String selection,
      String[] selectionArgs, String orderBy) {
 
    SQLiteDatabase db = helper.getWritableDatabase();
 
    Cursor cursor = null;
 
    int action = matcher.match(uri);
 
    switch (action) {
 
    case students:
 
      cursor = db.query("student", projection, selection, selectionArgs,
          null, null, orderBy);
 
      break;
 
    }
 
    System.out.println("-----------count:" + cursor.getCount());
 
    return cursor;
  }
 
  @Override
  public int update(Uri uri, ContentValues values, String selection,
      String[] arg3) {
 
    int count = -1;
 
    SQLiteDatabase db = helper.getWritableDatabase();
 
    int action = matcher.match(uri);
 
    switch (action) {
 
    case student:
      // 以id来处理更新
      long id = ContentUris.parseId(uri);
 
      String id_selection = "_id=" + id;
 
      if (selection != null && !selection.equals("")) {
 
        id_selection = id_selection + " and " + values;
 
      }
 
      count = db.update("student", values, id_selection, arg3);
 
      System.out.println("----------count:" + count);
 
      break;
    }
 
    return count;
  }
 
}

这个类很长,但是执行的方法都是比较常见的CURD的方法,重要的是UriMatcher和ContentUris类的使用。

接着执行单元测试类:Test

package com.app.contentprovider;
 
import android.content.ContentResolver;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.test.AndroidTestCase;
import android.util.Log;
 
public class Test extends AndroidTestCase {
 
  public void insert() {
 
    ContentResolver resolver = this.getContext().getContentResolver();
 
    String str = "content://com.app.wx/student";
 
    ContentValues values = new ContentValues();
 
    values.put("name", "wzq");
 
    values.put("age", 18);
 
    values.put("gender", "boy");
 
    resolver.insert(Uri.parse(str), values);
 
  }
 
  public void update() {
 
    ContentResolver resolver = this.getContext().getContentResolver();
 
    String str = "content://com.app.wx/student/2";
 
    ContentValues values = new ContentValues();
 
    values.put("name", "哈哈");
 
    resolver.update(Uri.parse(str), values, null, null);
 
  }
 
  public void query() {
 
    ContentResolver resolver = this.getContext().getContentResolver();
 
    String str = "content://com.app.wx/student";
 
    Uri uri = Uri.parse(str);
 
    Cursor cursor = resolver.query(uri, new String[] { "_id",
        "name,age,gender" }, null, null, "_id desc");
 
    Log.d("------count",cursor.getCount()+"");
  }
 
  public void delete() {
    ContentResolver resolver = this.getContext().getContentResolver();
 
    String str = "content://com.app.wx/student/2";
 
    Uri uri = Uri.parse(str);
 
    long id=resolver.delete(uri, null, null);
 
  }
 
}

执行insert方法之后(执行了三次):

2016421160332881.png (463×93)

执行了update方法之后:

2016421160354111.png (458×101)

执行了query方法之后:

2016421160411590.png (617×92)

执行了delete方法之后:

2016421160429449.png (513×79)

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