Scala&Android下的开发trait经验分享

前一段时间写了一个在Android中加入AdMob的博客，详见http://my.oschina.net/noahxiao/blog/61987

还有一个用Scala开发Android应用-使用trait与implicit优化Activity，详见http://my.oschina.net/noahxiao/blog/61720

首先说明一下，我在android下是采用scala语言开发的。并不想讨论太多语言的好坏。只是把我开发时的经验与大家分享一下。

class ScalaAndroidActivity extends Activity with AdMobAdvertising with TestDataSource1 with TestDataSource2

大家先不要晕scala语言的继承关系是可以这样写的。with...

1、trait AdMobAdvertising

package org.noahx.commonimport FindView._import android.app.Activityimport android.widget.LinearLayoutimport com.google.ads.AdViewimport com.google.ads.AdSizeimport com.google.ads.AdRequestimport android.os.Bundletrait AdMobAdvertising extends Activity with FindView {  def adLinearLayout: LinearLayout    def adUnitId:String="a14xxxxxxxxxx"  lazy val adView = new AdView(this, AdSize.BANNER, adUnitId)  override def onCreate(savedInstanceState: Bundle) = {    super.onCreate(savedInstanceState)    adLinearLayout.addView(adView)    adView.loadAd(new AdRequest())  }  override def onDestroy() = {    if (adView != null) {      adView.destroy()    }    super.onDestroy()  }}

以上就是我写的trait，这样我们可以不用太多考虑AdMob本身，只要实现adLinearLayout这个方法就可以了。来看看Activity

package org.noahx.scalaandroidimport android.app.Activityimport android.os.Bundleimport android.widget.Buttonimport android.widget.TextViewimport android.view.Viewimport org.noahx.common.FindView._import android.widget.LinearLayoutimport com.google.ads.AdViewimport com.google.ads.AdSizeimport com.google.ads.AdRequestimport org.noahx.common.AdMobAdvertisingclass ScalaAndroidActivity extends Activity with AdMobAdvertising {  lazy val text = findView[TextView](R.id.text1)  lazy val button = findView[Button](R.id.button1)  override def adLinearLayout = findView[LinearLayout](R.id.adLinearLayout) //注意这里决定AdMob放在哪个LinearLayout中  override def onCreate(savedInstanceState: Bundle) = {    setContentView(R.layout.main)  //这个要放在super之前    super.onCreate(savedInstanceState)    button.onClick { view: View =>      text.setText("hello scala1!!!")    }  }}

用这样一个AdMobAdvertising的trait只要在想加入AdMob的Activity中with一下，指定一个LinearLayout就可以了。

是不是看上去很干净

当然如果你的adUnitId号是变动的也可以override掉，在Activity中加入如下代码

override def adUnitId="xxxxxxxxxxxxxxxx"

2、trait BaseDataSource

在做完上面的模式后我在想，是不是访问sqlite数据时也可以这样来写呢

我们先看看BaseDataSource

package org.noahx.commonimport android.app.Activityimport android.database.sqlite.SQLiteDatabaseimport android.database.sqlite.SQLiteOpenHelperimport android.os.Bundletrait BaseDataSource extends Activity {  def getSQLiteOpenHelper(): SQLiteOpenHelper  val sqliteOpenHelper = getSQLiteOpenHelper()  var database: SQLiteDatabase = null    def getDatabase()=database  private def open() = {    database = sqliteOpenHelper.getWritableDatabase()  }  private def close() = {    database.close()  }  override def onCreate(savedInstanceState: Bundle) = {    super.onCreate(savedInstanceState)    open()  }  override def onResume() = {    open()    super.onResume()  }  override def onPause() {    close()    super.onPause()  }  override def onDestroy() = {    close()    super.onDestroy()  }}

我们可以看到这个也是继承Activity，里面已经定义好了何时创建连接，何时关闭连接。缺少的只是getSQLiteOpenHelper没有实现

下面我们来看看SQLiteOpenHelper，这个目前本身没什么特点。

package org.noahx.scalaandroidimport android.database.sqlite.SQLiteOpenHelperimport android.database.sqlite.SQLiteDatabase.CursorFactoryimport android.content.Contextimport android.database.sqlite.SQLiteDatabaseimport android.util.Logclass TestSQLiteOpenHelper(context: Context, dbName: String, cFactory: CursorFactory, ver: Int) extends SQLiteOpenHelper(context: Context, dbName: String, cFactory: CursorFactory, ver: Int) {  val databaseCreateTest1 = "create table test1 (id integer primary key autoincrement, name text not null)"  val databaseCreateTest2 = "create table test2 (id integer primary key autoincrement, name text not null)"  def this(context: Context) = {    this(context, "test.db", null, 1)  }  override def onCreate(database: SQLiteDatabase) = {    database.execSQL(databaseCreateTest1)    database.execSQL(databaseCreateTest2)  }  override def onUpgrade(db: SQLiteDatabase, oldVersion: Int, newVersion: Int) = {    Log.w(classOf[TestSQLiteOpenHelper].getName(), "Upgrading database from version " + oldVersion + " to " + newVersion + ", which will destroy all old data")    db.execSQL("DROP TABLE IF EXISTS " + "test1")    db.execSQL("DROP TABLE IF EXISTS " + "test2")    onCreate(db)  }}

下面我们要基于BaseDataSource写自己的DataSource了，这才是重点

（scala语言的定义与文件名无关，可以一个.scala文件中写多个class，trait,object，甚至全部程序写一个.scala文件中）

package org.noahx.scalaandroidimport org.noahx.common.BaseDataSourceimport scala.collection.mutable.ListBufferimport android.content.ContentValuestrait TestBaseDataSource extends BaseDataSource {  def getSQLiteOpenHelper() = new TestSQLiteOpenHelper(this)}trait TestDataSource1 extends TestBaseDataSource {  private val tableName = "test1"  def createTest1(name: String) = {    val values = new ContentValues()    values.put("name", name)    val insertId = database.insert(tableName, null, values)  }  def getTest1s(): List[String] = {    var words = new ListBuffer[String]    val cursor = database.query(tableName, Array("name"), null, null, null, null, null)    cursor.moveToFirst()    while (!cursor.isAfterLast()) {      words += cursor.getString(0)      cursor.moveToNext()    }    cursor.close()    words.toList  }}trait TestDataSource2 extends TestBaseDataSource {  private val tableName = "test2"  def createTest2(name: String) = {    val values = new ContentValues()    values.put("name", name)    val insertId = database.insert(tableName, null, values)  }  def getTest2s(): List[String] = {    var words = new ListBuffer[String]    val cursor = database.query(tableName, Array("name"), null, null, null, null, null)    cursor.moveToFirst()    while (!cursor.isAfterLast()) {      words += cursor.getString(0)      cursor.moveToNext()    }    cursor.close()    words.toList  }}

首先定义了TestBaseDataSource来统一设置helper，然后TestDataSource1与TestDataSource2就可以直接使用database这个对象了

来看看最终的Activity吧

package org.noahx.scalaandroidimport android.app.Activityimport android.os.Bundleimport android.widget.Buttonimport android.widget.TextViewimport android.view.Viewimport org.noahx.common.FindView._import android.widget.LinearLayoutimport com.google.ads.AdViewimport com.google.ads.AdSizeimport com.google.ads.AdRequestimport org.noahx.common.AdMobAdvertisingimport android.util.Logclass ScalaAndroidActivity extends Activity with AdMobAdvertising with TestDataSource1 with TestDataSource2 {  lazy val text = findView[TextView](R.id.text1)  lazy val button = findView[Button](R.id.button1)    override def adLinearLayout = findView[LinearLayout](R.id.adLinearLayout)  override def onCreate(savedInstanceState: Bundle) = {    setContentView(R.layout.main)    super.onCreate(savedInstanceState)        for(i <-0 to 10){      createTest1("test1."+i)      createTest2("test2."+i)    }    button.onClick { view: View =>      text.setText("hello scala!!!")            Log.i(classOf[ScalaAndroidActivity].getName(),getTest1s().toString())      Log.i(classOf[ScalaAndroidActivity].getName(),getTest2s().toString())    }  }}

这样的效果就是如果哪个Activity想用TestDataSource1，就直接加到父行为中，并在这个Activity中可以直接调用如：createTest1这样的方法直接操作数据库

由以下代码来写数据库

for(i <-0 to 10){      createTest1("test1."+i)      createTest2("test2."+i)    }

onClick时由Log输出结果

      Log.i(classOf[ScalaAndroidActivity].getName(),getTest1s().toString())      Log.i(classOf[ScalaAndroidActivity].getName(),getTest2s().toString())

后台打印结果如下

1、trait AdMobAdvertising

2、trait BaseDataSource

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