从Java到Scala: SensorManager

Question

Scala/Android新手问题。我正在尝试将这段简单的代码从Java重写为Scala。Java工作代码：

private final SensorEventListener mAccListener = new SensorEventListener() {
    public void onSensorChanged(SensorEvent event) {
        // ... some code
    }
};


@Override    
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    findViewById(R.id.start).setOnClickListener(this);        

    mSensorManager = (SensorManager)getSystemService(Context.SENSOR_SERVICE);
    mAccSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);

    mSensorManager.registerListener(mAccListener, mAccSensor,
            SensorManager.SENSOR_DELAY_GAME);
}

...and Scala：

package com.example.hello

import android.app.Activity
import android.content.Context
import android.content.Context
import android.hardware.Sensor
import android.hardware.SensorManager
import android.os.Bundle
import android.os.Bundle
import android.view.View.OnClickListener
import android.view.View
import android.view.View
import android.widget.Toast
import android.widget.Toast
import android.hardware.SensorEventListener

class HelloAndroid extends Activity {

  def mAccListener (v: View) {
    // ... some code
  }

  override def onCreate(savedInstanceState : Bundle) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.main)

    findViewById(R.id.start).setOnClickListener(new View.OnClickListener() {
      def onClick(v: View) {
        Toast.makeText(v.getContext, "Hello World", Toast.LENGTH_LONG).show()
      }
    })

        val mSensorManager = getSystemService(Context.SENSOR_SERVICE).asInstanceOf[SensorManager]
        val mAccSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER)

        mSensorManager.registerListener(mAccListener(_), mAccSensor,
                SensorManager.SENSOR_DELAY_GAME)

  }
}

错误是Eclipe状态：

Multiple markers at this line
    - missing arguments for method mAccListener in class HelloAndroid; follow this method with `_' if you want to treat it as a partially applied function
    - overloaded method value registerListener with alternatives: (android.hardware.SensorEventListener,android.hardware.Sensor,Int,android.os.Handler)Boolean <and> 
     (android.hardware.SensorEventListener,android.hardware.Sensor,Int)Boolean <and> (android.hardware.SensorListener,Int,Int)Boolean <and> (android.hardware.SensorListener,Int)Boolean 
     cannot be applied to (android.view.View => Unit, android.hardware.Sensor, Int)

据我所知，Scala找不到从哪个类调用方法？我怎么才能修复它？

Answer 1

"mAccListener(_)“创建类型为android.view.View => Unit的函数。但是没有任何版本的registerListener可以使用这样的函数。

Java版本传入了一个SensorListener。Scala版本不应该做同样的事情吗？

您可能正在考虑从视图=>单元到SensorListener的隐式转换……如果是这样，您需要自己构建它。

Answer 2

经过以下修正后，它才能正常工作：

class HelloAndroid extends Activity {

    def mAccListener() :SensorListener = new SensorListener {
        def onSensorChanged(x1: Int, x2: Array[Float]) = {
            var t=findViewById(R.id.acc).asInstanceOf[TextView]
            var x = x2(0).toString
            t.setText(x)
        }

        def onAccuracyChanged(a: Int, b: Int) = {
          //TODO
        }
    }

    override def onCreate(savedInstanceState : Bundle) {

    //...            

        mSensorManager.registerListener(mAccListener, SensorManager.SENSOR_DELAY_GAME)

  }
}

但我不明白的是，为什么在Java和Scala中，相同的函数会有不同的值。它既不方便，也令人困惑：

+-------------------+------------------------------+---------------------------+
| Api Function      | Java                         | Scala                     |
+-------------------+------------------------------+---------------------------+
| onSensorChanged   | SensorEvent event            | x1: Int, x2: Array[Float] |
| onAccuracyChanged | Sensor sensor, int accuracy  | a: Int, b: Int            |
+-------------------+------------------------------+---------------------------+

有人能解释一下吗？