SimpleCursorAdapter 原理和实例

SimpleCursorAdapter

1. 原理参见下面代码注释

  Cursor cursor = dbHelper.fetchAllCountries(); //cursor中存储需要加载到listView中的条目，可能由一行或者多行组成。每一行可能包含多列数据（多于listview中定义的）

  //the desired columns to be bound
  String[] columns = new String[] {
    CountryDb.KEY_CODE,
    CountryDb.KEY_NAME,
    CountryDb.KEY_CONTINENT
  }; //这个数据结构指定cursor中的那些列将显示到listview每一行中（从多列中挑选需要的）

  //the XML defined views which the data will be bound to
  int[] to = new int[] {
    R.id.code,
    R.id.name,
    R.id.continent
  };//这个数据结构定义listview中各组件的id，由此和上面的的colums形成了map关系，即cursor中某一行的列字段映射到listview中的控件

  //create the adapter using the cursor pointing to the desired data
  //as well as the layout information
  SimpleCursorAdapter dataAdapter = new SimpleCursorAdapter(
    this, R.layout.list_row, //listView xml控件名
    cursor, //所存数据的cursor
    columns,//cursor需要的字段定义
    to, //映射到XML每个控件的定义
    0);

  ListView listView = (ListView) findViewById(R.id.listView1);
  // Assign adapter to ListView
  listView.setAdapter(dataAdapter); //设置adapter，所有cursor中的数据将自动加载

2. 附上一个通过实现SimpleCursorAdapter getView（）方法设置行背景颜色的例子

该例子通过检索SQLite数据库构建了基本的listView，但是默认的listView的行条目是不带有斑马线的（相邻行背景颜色不同）。通过继承SimpleCursorAdapter并实现getView（）方法可以达到目的。

Main Activity Layout - activity_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=".MainActivity"
    android:padding="10dp" >

    <ListView
        android:id="@+id/listView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true">
    </ListView>

</RelativeLayout>

ListView Row Layout - list_row.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="5dip" >

    <TextView
        android:id="@+id/name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:text="Medium Text"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/name"
        android:layout_toRightOf="@+id/name"
        android:text=" - "
        android:textAppearance="?android:attr/textAppearanceMedium" />

    <TextView
        android:id="@+id/code"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_toRightOf="@+id/textView1"
        android:text="Medium Text"
        android:textAppearance="?android:attr/textAppearanceMedium" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="false"
        android:layout_alignParentLeft="true"
        android:layout_below="@id/name"
        android:text="Continent is "
        android:textAppearance="?android:attr/textAppearanceMedium" />

    <TextView
        android:id="@+id/continent"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/textView2"
        android:layout_alignBottom="@+id/textView2"
        android:layout_toRightOf="@+id/textView2"
        android:text="Medium Text"
        android:textAppearance="?android:attr/textAppearanceMedium" />

</RelativeLayout>

Country POJO - Country.java

package com.as400samplecode;

public class Country {

 String code = null;
 String name = null;
 String continent = null;

 public String getCode() {
  return code;
 }
 public void setCode(String code) {
  this.code = code;
 }
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
 public String getContinent() {
  return continent;
 }
 public void setContinent(String continent) {
  this.continent = continent;
 }

}

Country SQLite Db Adapter - CountryDb.java

package com.as400samplecode;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class CountryDb {

 public static final String KEY_ROWID = "_id";
 public static final String KEY_CODE = "code";
 public static final String KEY_NAME = "name";
 public static final String KEY_CONTINENT = "continent";

 private static final String TAG = "CountriesDbAdapter";
 private DatabaseHelper mDbHelper;
 private SQLiteDatabase mDb;

 private static final String DATABASE_NAME = "World";
 private static final String SQLITE_TABLE = "Country";
 private static final int DATABASE_VERSION = 1;

 private final Context mCtx;

 private static final String DATABASE_CREATE =
  "CREATE TABLE if not exists " + SQLITE_TABLE + " (" +
  KEY_ROWID + " integer PRIMARY KEY autoincrement," +
  KEY_CODE + "," +
  KEY_NAME + "," +
  KEY_CONTINENT + "," +
  " UNIQUE (" + KEY_CODE +"));";

 private static class DatabaseHelper extends SQLiteOpenHelper {

  DatabaseHelper(Context context) {
   super(context, DATABASE_NAME, null, DATABASE_VERSION);
  }

  @Override
  public void onCreate(SQLiteDatabase db) {
   Log.w(TAG, DATABASE_CREATE);
   db.execSQL(DATABASE_CREATE);
  }

  @Override
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
   Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
     + newVersion + ", which will destroy all old data");
   db.execSQL("DROP TABLE IF EXISTS " + SQLITE_TABLE);
   onCreate(db);
  }
 }

 public CountryDb(Context ctx) {
  this.mCtx = ctx;
 }

 public CountryDb open() throws SQLException {
  mDbHelper = new DatabaseHelper(mCtx);
  mDb = mDbHelper.getWritableDatabase();
  return this;
 }

 public void close() {
  if (mDbHelper != null) {
   mDbHelper.close();
  }
 }

 public long createCountry(String code, String name, String continent) {

  ContentValues initialValues = new ContentValues();
  initialValues.put(KEY_CODE, code);
  initialValues.put(KEY_NAME, name);
  initialValues.put(KEY_CONTINENT, continent);

  return mDb.insert(SQLITE_TABLE, null, initialValues);
 }

 public boolean deleteAllCountries() {

  int doneDelete = 0;
  doneDelete = mDb.delete(SQLITE_TABLE, null , null);
  Log.w(TAG, Integer.toString(doneDelete));
  return doneDelete > 0;

 }

 public Cursor fetchAllCountries() {

  Cursor mCursor = mDb.query(SQLITE_TABLE, new String[] {KEY_ROWID,
    KEY_CODE, KEY_NAME, KEY_CONTINENT},
    null, null, null, null, null);

  if (mCursor != null) {
   mCursor.moveToFirst();
  }
  return mCursor;
 }

 public void insertSomeCountries() {

  createCountry("AFG","Afghanistan","Asia");
  createCountry("CHN","China","Asia");
  createCountry("ALB","Albania","Europe");
  createCountry("DZA","Algeria","Africa");
  createCountry("ASM","American Samoa","Oceania");
  createCountry("AND","Andorra","Europe");
  createCountry("AGO","Angola","Africa");
  createCountry("AIA","Anguilla","North America");
  createCountry("USA","United States","North America");
  createCountry("CAN","Canada","North America");

 }

}

Android Main Activity - MainActivity.java

package com.as400samplecode;

import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.database.Cursor;
import android.graphics.Color;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;

public class MainActivity extends Activity {

 private CountryDb dbHelper;

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

  dbHelper = new CountryDb(this);
  dbHelper.open();

  //Clean all data
  dbHelper.deleteAllCountries();
  //Add some data
  dbHelper.insertSomeCountries();

  //Generate ListView from SQLite Database
  displayListView();

 }

 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
  // Inflate the menu; this adds items to the action bar if it is present.
  getMenuInflater().inflate(R.menu.activity_main, menu);
  return true;
 }

 private void displayListView() {

  Cursor cursor = dbHelper.fetchAllCountries();

  //the desired columns to be bound
  String[] columns = new String[] {
    CountryDb.KEY_CODE,
    CountryDb.KEY_NAME,
    CountryDb.KEY_CONTINENT
  };

  //the XML defined views which the data will be bound to
  int[] to = new int[] {
    R.id.code,
    R.id.name,
    R.id.continent
  };

  //create the adapter using the cursor pointing to the desired data
  //as well as the layout information
  MyCursorAdapter dataAdapter = new MyCursorAdapter(
    this, R.layout.list_row,
    cursor,
    columns,
    to,
    0);

  ListView listView = (ListView) findViewById(R.id.listView1);
  // Assign adapter to ListView
  listView.setAdapter(dataAdapter);

 }

 //extend the SimpleCursorAdapter to create a custom class where we
 //can override the getView to change the row colors
 private class MyCursorAdapter extends SimpleCursorAdapter{

  public MyCursorAdapter(Context context, int layout, Cursor c,
    String[] from, int[] to, int flags) {
   super(context, layout, c, from, to, flags);
  } 

  @Override
  public View getView(int position, View convertView, ViewGroup parent) { 

   //get reference to the row
   View view = super.getView(position, convertView, parent);
   //check for odd or even to set alternate colors to the row background
   if(position % 2 == 0){
    view.setBackgroundColor(Color.rgb(238, 233, 233));
   }
   else {
    view.setBackgroundColor(Color.rgb(255, 255, 255));
   }
   return view;
  } 

 } 

}