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 Android教程網 >> Android技術 >> 關於Android編程 >> 實例講解Android中ContentProvider組件的使用方法

實例講解Android中ContentProvider組件的使用方法

編輯:關於Android編程

ContentProvider基本使用
為了在應用程序之間交換數據,android提供了ContentProvider,ContentProvider是不同應用程序之間進行數據交換的標准API,當一個應用程序需要把自己的數據暴露給其他程序使用時,該應用程序就可以通過提供ContentPRovider來實現,其他應用程序就可以通過ContentResolver來操作ContentProvider暴露的數據。

實現ContentProvider的步驟:

1)編寫一個類,繼承ContentProvider,並且重寫裡面的CRUD方法。

2)在androidmanifest.xml文件中注冊provider。

在androidmanifest.xml中注冊provider需要以下3個屬性:

             android:name              provider的實現類。

             android:authorities       provider的uri。

             android:exported          provider是否暴露給其他程序。


ContentResovler操作ContentProvider:

1)獲取ContentResolver,getContentResovler()方法來自於ContextWrapper,所以activity和service中都可以使用。

2)調用CURD方法,通過參數url,調用指定的ContentProvider的方法。


下面是一個demo,向contentProvider中插入一條數據,並且返回到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類

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類

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的顯示界面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);
 
  }
 
}

實現效果:(執行了3次插入後的效果)

2016421160202125.png (720×1280)

ContentProvider的單元測試
ContentProvider是android的四大組件之一,在編寫代碼的時候最好是加上單元測試,這樣可以確定對數據的CRUD的正確。本篇文章主要介紹ContentProvider中兩個主要輔助類的使用還有單元測試的在ContentProvider中的使用。

需要用到的兩個輔助類:UriMatcher類和ContentUris類。

UriMatcher類:能夠對輸入的uri參數就行匹配,以確定對什麼表執行什麼樣的操作。

ContentUris類:有些方法需要返回uri,運用此類可以方便的生成uri類。

對於單元測試,個人覺得非常有必要在今後寫代碼的時候使用,這樣可以非常准確的確定代碼的正確性。

使用單元測試的步驟:

 1)加入instrumentation,這個部分的代碼是固定,也可以完全在ADT提供的向導中導入。

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

2)添加<uses-library>,這個部分的代碼也是固定的寫法。

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


好了,必備的知識已經講完了,現在上代碼:

1)生成一個SQLiteDatabase類,這個是必需的類MySQLiteOpenHelper類

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) {
       //建表語句
    String create_student = "create table student(_id integer primary key autoincrement,name varchar(10),age integer,gender vachar(10))";
     
    db.execSQL(create_student);
       //千萬不能執行這句  // db.close();
 
  }
 
  @Override
  public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
 
  }
 
}

 
然後添加我們需要的MyContentProvider類:

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);
 
  // 匹配單條記錄
  private static final int student = 1;
  // 匹配多條記錄
  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) {
     
    // 匹配單條記錄
    case student:
 
      long id = ContentUris.parseId(uri);
     //獲取單條記錄的id號
      String delete_id = "_id=" + id;
 
      if (selection != null) {
        delete_id += delete_id + " and " + selection;
      }
 
      db.delete("student", delete_id, selectionArgs);
 
      break;
       
    // 匹配多條記錄
    case students:
 
      db.delete("student", selection, selectionArgs);
 
      break;
    }
     
    return 0;
  }
 
  //必需實現這個方法,這個方法與intent有關系,以後再講
  @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來處理更新
      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;
  }
 
}

這個類很長,但是執行的方法都是比較常見的CURD的方法,重要的是UriMatcher和ContentUris類的使用。

接著執行單元測試類: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);
 
  }
 
}

執行insert方法之後(執行了三次):

2016421160332881.png (463×93)

執行了update方法之後:

2016421160354111.png (458×101)

執行了query方法之後:

2016421160411590.png (617×92)

執行了delete方法之後:

2016421160429449.png (513×79)

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