Implement a Simple Horizontal Indicator using SensorManager and SensorEventListener

In the former articles, "Detect rotation around X, Y & Z axis, using SensorManager and SensorEventListener" and "Implement a Simple Compass using SensorManager and SensorEventListener" have been describe. In this article, I will show how to implement a Horizontal Indicator.

A point float on the screen to indicate horizontal of the phone.



Create a custom view, HorizontalView.java, extends View. It display the drawing of our indicator.

package com.exercise.AndroidHorizontal;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

public class HorizontalView extends View {
 
 private float pitch = 0, roll = 0;
 private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
 private boolean firstDraw;
 final float radiusPt = (float)3;

 public HorizontalView(Context context) {
  super(context);
  // TODO Auto-generated constructor stub
  init();
 }

 public HorizontalView(Context context, AttributeSet attrs) {
  super(context, attrs);
  // TODO Auto-generated constructor stub
  init();
 }

 public HorizontalView(Context context, AttributeSet attrs, int defStyle) {
  super(context, attrs, defStyle);
  // TODO Auto-generated constructor stub
  init();
 }
 
 private void init(){
  
  paint.setStyle(Paint.Style.STROKE);
  paint.setStrokeWidth(3);
  paint.setColor(Color.WHITE);
  paint.setTextSize(20);
  
  firstDraw = true; 
 }

 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  // TODO Auto-generated method stub
  setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec), MeasureSpec.getSize(heightMeasureSpec));
 }

 @Override
 protected void onDraw(Canvas canvas) {
  // TODO Auto-generated method stub
  
  int cxPlan = getMeasuredWidth()/2;
  int cyPlan = getMeasuredHeight()/2;

  float fullLength, halfLength, ptPerDegree;
  
  if(cxPlan > cyPlan){
   fullLength = (float)(getMeasuredHeight() * 0.9);
   
  }
  else{
   fullLength = (float)(getMeasuredWidth() * 0.9); 
  }
  halfLength = fullLength/2;
  ptPerDegree = fullLength/360;
  
  canvas.drawRect(cxPlan-halfLength, cyPlan-halfLength,
    cxPlan+halfLength, cyPlan+halfLength, paint);
  
  canvas.drawRect(0, 0, getMeasuredWidth(), getMeasuredHeight(), paint);
  
  if(!firstDraw){
   float yPt = cyPlan + (pitch * ptPerDegree);
   float xPt = cxPlan + (roll * ptPerDegree);
   canvas.drawCircle(xPt, yPt, radiusPt, paint);
  } 
 }

 public void updateHorizontal(float tPitch, float tRoll)
 {
  firstDraw = false;
  pitch = tPitch;
  roll = tRoll;
  invalidate();
 }
}

Modify the layout file, main.xml, to add HorizontalView.

   android:orientation="vertical"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   >
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="@string/hello"
   />
   android:id="@+id/textpitch"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
   android:id="@+id/textroll"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
 class="com.exercise.AndroidHorizontal.HorizontalView"
 android:id="@+id/myhorizontalview"
 android:layout_width="fill_parent"
 android:layout_height="fill_parent"
/>

Modify the main code, AndroidHorizontal.java, to handle SensorManager and SensorEventListener.

package com.exercise.AndroidHorizontal;

import java.util.List;

import android.app.Activity;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.widget.TextView;
import android.widget.Toast;

public class AndroidHorizontal extends Activity {
 
 private static SensorManager mySensorManager;
 private boolean sersorrunning;
 private HorizontalView myHorizontalView;
 private TextView textviewPitch, textviewRoll;
 
   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.main);
      
       myHorizontalView = (HorizontalView)findViewById(R.id.myhorizontalview);
       textviewPitch = (TextView)findViewById(R.id.textpitch);
       textviewRoll = (TextView)findViewById(R.id.textroll);
      
       mySensorManager = (SensorManager)getSystemService(Context.SENSOR_SERVICE);
       List mySensors = mySensorManager.getSensorList(Sensor.TYPE_ORIENTATION);
      
       if(mySensors.size() > 0){
        mySensorManager.registerListener(mySensorEventListener, mySensors.get(0), SensorManager.SENSOR_DELAY_NORMAL);
        sersorrunning = true;
        Toast.makeText(this, "Start ORIENTATION Sensor", Toast.LENGTH_LONG).show(); 
       }
       else{
        Toast.makeText(this, "No ORIENTATION Sensor", Toast.LENGTH_LONG).show();
        sersorrunning = false;
        finish(); 
       }
   }
  
   private SensorEventListener mySensorEventListener = new SensorEventListener(){

  @Override
  public void onAccuracyChanged(Sensor sensor, int accuracy) {
   // TODO Auto-generated method stub
   
  }

  @Override
  public void onSensorChanged(SensorEvent event) {
   // TODO Auto-generated method stub
   
   textviewPitch.setText("Pitch: " + String.valueOf(event.values[1]));
         textviewRoll.setText("Roll: " + String.valueOf(event.values[2]));
   
   myHorizontalView.updateHorizontal(
     (float)event.values[1], (float)event.values[2]);
  }
    
   };

 @Override
 protected void onDestroy() {
  // TODO Auto-generated method stub
  super.onDestroy();
  
  if(sersorrunning){
   mySensorManager.unregisterListener(mySensorEventListener); 
  }
 }
  
  
}

Modify AndroidManifest.xml to disable the auto-rotate feature, otherwise it will point to wrong direction.

Download the files.