Android SensorCompass (basic)

CompassActivity.java

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.view.View;
import android.widget.RelativeLayout;

public class CompassActivity extends Activity implements SensorEventListener {

	@SuppressWarnings("unused")
	private String TAG = "SensorCompass";

	// Main View
	private RelativeLayout mFrame;

	// Sensors & SensorManager
	private Sensor accelerometer;
	private Sensor magnetometer;
	private SensorManager mSensorManager;

	// Storage for Sensor readings
	private float[] mGravity = null;
	private float[] mGeomagnetic = null;

	// Rotation around the Z axis
	private double mRotationInDegress;

	// View showing the compass arrow
	private CompassArrowView mCompassArrow;

	@Override
	protected void onCreate(Bundle savedInstanceState) {

		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);

		mFrame = (RelativeLayout) findViewById(R.id.frame);

		mCompassArrow = new CompassArrowView(getApplicationContext());

		mFrame.addView(mCompassArrow);

		// Get a reference to the SensorManager
		mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);

		// Get a reference to the accelerometer
		accelerometer = mSensorManager
				.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);

		// Get a reference to the magnetometer
		magnetometer = mSensorManager
				.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);

		// Exit unless both sensors are available
		if (null == accelerometer || null == magnetometer)
			finish();

	}

	@Override
	protected void onResume() {
		super.onResume();


		// Register for sensor updates

		mSensorManager.registerListener(this, accelerometer,
				SensorManager.SENSOR_DELAY_NORMAL);

		mSensorManager.registerListener(this, magnetometer,
				SensorManager.SENSOR_DELAY_NORMAL);
	}

	@Override
	protected void onPause() {
		super.onPause();

		// Unregister all sensors
		mSensorManager.unregisterListener(this);

	}

	@Override
	public void onSensorChanged(SensorEvent event) {

		// Acquire accelerometer event data
		
		if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {

			mGravity = new float[3];
			System.arraycopy(event.values, 0, mGravity, 0, 3);

		} 
		
		// Acquire magnetometer event data
		
		else if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD) {

			mGeomagnetic = new float[3];
			System.arraycopy(event.values, 0, mGeomagnetic, 0, 3);

		}

		// If we have readings from both sensors then
		// use the readings to compute the device's orientation
		// and then update the display.

		if (mGravity != null && mGeomagnetic != null) {

			float rotationMatrix[] = new float[9];

			// Users the accelerometer and magnetometer readings
			// to compute the device's rotation with respect to
			// a real world coordinate system

			boolean success = SensorManager.getRotationMatrix(rotationMatrix,
					null, mGravity, mGeomagnetic);

			if (success) {

				float orientationMatrix[] = new float[3];

				// Returns the device's orientation given
				// the rotationMatrix

				SensorManager.getOrientation(rotationMatrix, orientationMatrix);

				// Get the rotation, measured in radians, around the Z-axis
				// Note: This assumes the device is held flat and parallel
				// to the ground

				float rotationInRadians = orientationMatrix[0];

				// Convert from radians to degrees
				mRotationInDegress = Math.toDegrees(rotationInRadians);

				// Request redraw
				mCompassArrow.invalidate();

				// Reset sensor event data arrays
				mGravity = mGeomagnetic = null;

			}
		}

	}

	@Override
	public void onAccuracyChanged(Sensor sensor, int accuracy) {
		// N/A
	}

	public class CompassArrowView extends View {

		Bitmap mBitmap = BitmapFactory.decodeResource(getResources(),
				R.drawable.arrow);
		int mBitmapWidth = mBitmap.getWidth();

		// Height and Width of Main View
		int mParentWidth;
		int mParentHeight;

		// Center of Main View
		int mParentCenterX;
		int mParentCenterY;

		// Top left position of this View
		int mViewTopX;
		int mViewLeftY;

		public CompassArrowView(Context context) {
			super(context);
		};

		// Compute location of compass arrow
		@Override
		protected void onSizeChanged(int w, int h, int oldw, int oldh) {
			mParentWidth = mFrame.getWidth();
			mParentHeight = mFrame.getHeight();

			mParentCenterX = mParentWidth / 2;
			mParentCenterY = mParentHeight / 2;

			mViewLeftY = mParentCenterX - mBitmapWidth / 2;
			mViewTopX = mParentCenterY - mBitmapWidth / 2;
		}

		// Redraw the compass arrow
		@Override
		protected void onDraw(Canvas canvas) {

			// Save the canvas
			canvas.save();

			// Rotate this View
			canvas.rotate((float) -mRotationInDegress, mParentCenterX,
					mParentCenterY);

			// Redraw this View
			canvas.drawBitmap(mBitmap, mViewLeftY, mViewTopX, null);

			// Restore the canvas
			canvas.restore();

		}
	}
}

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

213

import android.app.Activity;

import android.content.Context;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.graphics.Canvas;

import android.hardware.Sensor;

import android.hardware.SensorEvent;

import android.hardware.SensorEventListener;

import android.hardware.SensorManager;

import android.os.Bundle;

import android.view.View;

import android.widget.RelativeLayout;

public class CompassActivity extends Activity implements SensorEventListener {

@SuppressWarnings("unused")

private String TAG = "SensorCompass";

// Main View

private RelativeLayout mFrame;

// Sensors & SensorManager

private Sensor accelerometer;

private Sensor magnetometer;

private SensorManager mSensorManager;

// Storage for Sensor readings

private float[] mGravity = null;

private float[] mGeomagnetic = null;

// Rotation around the Z axis

private double mRotationInDegress;

// View showing the compass arrow

private CompassArrowView mCompassArrow;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

mFrame = (RelativeLayout) findViewById(R.id.frame);

mCompassArrow = new CompassArrowView(getApplicationContext());

mFrame.addView(mCompassArrow);

// Get a reference to the SensorManager

mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);

// Get a reference to the accelerometer

accelerometer = mSensorManager

.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);

// Get a reference to the magnetometer

magnetometer = mSensorManager

.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);

// Exit unless both sensors are available

if (null == accelerometer || null == magnetometer)

finish();

}

@Override

protected void onResume() {

super.onResume();

// Register for sensor updates

mSensorManager.registerListener(this, accelerometer,

SensorManager.SENSOR_DELAY_NORMAL);

mSensorManager.registerListener(this, magnetometer,

SensorManager.SENSOR_DELAY_NORMAL);

}

@Override

protected void onPause() {

super.onPause();

// Unregister all sensors

mSensorManager.unregisterListener(this);

}

@Override

public void onSensorChanged(SensorEvent event) {

// Acquire accelerometer event data

if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {

mGravity = new float[3];

System.arraycopy(event.values, 0, mGravity, 0, 3);

}

// Acquire magnetometer event data

else if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD) {

mGeomagnetic = new float[3];

System.arraycopy(event.values, 0, mGeomagnetic, 0, 3);

}

// If we have readings from both sensors then

// use the readings to compute the device's orientation

// and then update the display.

if (mGravity != null && mGeomagnetic != null) {

float rotationMatrix[] = new float[9];

// Users the accelerometer and magnetometer readings

// to compute the device's rotation with respect to

// a real world coordinate system

boolean success = SensorManager.getRotationMatrix(rotationMatrix,

null, mGravity, mGeomagnetic);

if (success) {

float orientationMatrix[] = new float[3];

// Returns the device's orientation given

// the rotationMatrix

SensorManager.getOrientation(rotationMatrix, orientationMatrix);

// Get the rotation, measured in radians, around the Z-axis

// Note: This assumes the device is held flat and parallel

// to the ground

float rotationInRadians = orientationMatrix[0];

// Convert from radians to degrees

mRotationInDegress = Math.toDegrees(rotationInRadians);

// Request redraw

mCompassArrow.invalidate();

// Reset sensor event data arrays

mGravity = mGeomagnetic = null;

}

@Override

public void onAccuracyChanged(Sensor sensor, int accuracy) {

// N/A

}

public class CompassArrowView extends View {

Bitmap mBitmap = BitmapFactory.decodeResource(getResources(),

R.drawable.arrow);

int mBitmapWidth = mBitmap.getWidth();

// Height and Width of Main View

int mParentWidth;

int mParentHeight;

// Center of Main View

int mParentCenterX;

int mParentCenterY;

// Top left position of this View

int mViewTopX;

int mViewLeftY;

public CompassArrowView(Context context) {

super(context);

};

// Compute location of compass arrow

@Override

protected void onSizeChanged(int w, int h, int oldw, int oldh) {

mParentWidth = mFrame.getWidth();

mParentHeight = mFrame.getHeight();

mParentCenterX = mParentWidth / 2;

mParentCenterY = mParentHeight / 2;

mViewLeftY = mParentCenterX - mBitmapWidth / 2;

mViewTopX = mParentCenterY - mBitmapWidth / 2;

}

// Redraw the compass arrow

@Override

protected void onDraw(Canvas canvas) {

// Save the canvas

canvas.save();

// Rotate this View

canvas.rotate((float) -mRotationInDegress, mParentCenterX,

mParentCenterY);

// Redraw this View

canvas.drawBitmap(mBitmap, mViewLeftY, mViewTopX, null);

// Restore the canvas

canvas.restore();

}

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ffffffff" 
    android:id="@+id/frame">

</RelativeLayout>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:background="#ffffffff"

android:id="@+id/frame">

</RelativeLayout>