QuartzTestView.h

An object QuartzTestView is a new view we are creating.

We will set an object of this class to be the view used by our view controller.

#import <UIKit/UIKit.h>
#import "Constants.h"

@interface QuartzTestView : UIView
@property (nonatomic, assign) CGPoint firstTouch; //assign keywords since C type
@property (nonatomic, assign) CGPoint lastTouch;
@property (nonatomic, assign) ShapeType shapeType;
@property (nonatomic, assign)  BOOL useRandomColor;
@property (nonatomic, strong) UIColor *currentColor;
@property (nonatomic, strong) UIImage *drawImage;
@end

As this class is going to respond to touch events we have properties for the start and current location of touch.
As we will support multiple colors we have a property for the currentColor and another for whether to use a random color; we will draw different shapes so have for the current shape. We also have a property that we will use to hold an image resource that we will also be able to draw.

QuartzTestView.m

Here is the implementation of QuartzTestView. The drawRect method is where we override the base UIView ways of drawing things. We also have code to handle touch events (when they start, end and how they change).


#import "QuartzTestView.h"
#import "UIRandomColor.h"

@implementation QuartzTestView
//we're using initWithCoder as we are loading the view from a nib
// and so init and initWithFrame will never be called
-(id)initWithCoder:(NSCoder *)coder
{
    if((self = [super initWithCoder:coder])) {
        _currentColor = [UIColor redColor];
        _useRandomColor = NO;
        _drawImage = [UIImage imageNamed:@"myphoto.jpg"];
    }
    return self;
}


// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextSetLineWidth(context, 2.0);
    CGContextSetStrokeColorWithColor(context, _currentColor.CGColor);
    CGContextSetFillColorWithColor(context, _currentColor.CGColor);

    CGRect currentRect = CGRectMake((_firstTouch.x > _lastTouch.x) ? _lastTouch.x : _firstTouch.x,
                                    (_firstTouch.y > _lastTouch.y) ? _lastTouch.y : _lastTouch.y,
                                    fabsf(_firstTouch.x - _lastTouch.x),
                                    fabsf(_firstTouch.y - _lastTouch.y));
    switch (_shapeType)
    {
        case kLineShape:
            CGContextMoveToPoint(context, _firstTouch.x, _firstTouch.y);
            CGContextAddLineToPoint(context, _lastTouch.x, _lastTouch.y);
            CGContextStrokePath(context);
            break;

        case kRectShape:
            CGContextAddRect(context, currentRect);
            CGContextDrawPath(context, kCGPathFillStroke);
            break;

        case kEllipseShape:
            CGContextAddEllipseInRect(context, currentRect);
            CGContextDrawPath(context, kCGPathFillStroke);
            break;

        case kImageShape: {
            CGFloat horizontalOffset = _drawImage.size.width/2;

            CGFloat verticalOffset = _drawImage.size.height/2;
            CGPoint drawPoint = CGPointMake(_lastTouch.x - horizontalOffset,
                                            _lastTouch.y - verticalOffset);
            [_drawImage drawAtPoint:drawPoint];
            break;
        }
        default:
            break;
    }
}

// Basic idea for touch handlers is to store in fields the touch info and redraw
- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    if(_useRandomColor) {
        self.currentColor = [UIColor randomColor];
    }
    UITouch *touch = [touches anyObject];
    _firstTouch = [touch locationInView:self]; //store touch start info
    _lastTouch = [touch locationInView:self];
    NSLog(@"hi there");
    [self setNeedsDisplay]; // redraw view
}
- (void) touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event {
    NSLog(@"hi there");
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSLog(@"hi there");
    UITouch *touch = [touches anyObject];
    _lastTouch = [touch locationInView:self];
    [self setNeedsDisplay]; // redraw view
    
}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSLog(@"hi there");
    UITouch *touch = [touches anyObject];
    _lastTouch = [touch locationInView:self];
    [self setNeedsDisplay]; // redraw view
    
}
@end

QuartzTestViewController.h

The view controller class is responsible for handler events from the two segmented controls. To do this we have methods changeColor and changeShape.

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController

@property (weak, nonatomic) IBOutlet UISegmentedControl *colorControl;

@end

We have an IBOutlet for the color segmented control, because when someone is drawing an image they can't select a color for the image so we turn off the color segmented control. Thus, we need a reference to it to do this.

QuartzTestViewController.m

The implementation of changeColor and changeShape is pretty straightforward:

#import "ViewController.h"
#import "Constants.h"
#import "UIRandomColor.h"
#import "QuartzTestView.h"

@interface ViewController ()

@end

@implementation ViewController

- (IBAction)changeShape:(id)sender {
    UISegmentedControl *control = sender;
    ShapeType index = (ShapeType)[control selectedSegmentIndex];
    [(QuartzTestView *)self.view setShapeType: index];
    if(index == kImageShape)
        self.colorControl.hidden = YES;
    else
        self.colorControl.hidden = NO;
}
- (IBAction)changeColor:(id)sender {
    UISegmentedControl *control = sender;
    NSInteger index = [control selectedSegmentIndex];

    QuartzTestView *quartzView = (QuartzTestView *)self.view;

    switch (index)
    {
        case kRedColorTab:
            quartzView.currentColor = [UIColor redColor];
            quartzView.useRandomColor = NO;
            break;
        case kBlueColorTab:
            quartzView.currentColor = [UIColor blueColor];
            quartzView.useRandomColor = NO;
            break;
        case kYellowColorTab:
            quartzView.currentColor = [UIColor yellowColor];
            quartzView.useRandomColor = NO;
            break;
        case kGreenColorTab:
            quartzView.currentColor = [UIColor greenColor];
            quartzView.useRandomColor = NO;
            break;
        case kRandomColorTab:
            quartzView.useRandomColor = YES;
            break;
        default:
            break;
    }
}

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

QuartzTestViewController Storyboard

To complete the project we open main storyboard in interface builder, we click on the view then switch to the identity inspector and make sure the class of the view is changed from UIView to QuartzTestView.
We drag out two segmented controls.
For the color one, in the control attributes we set that it has five segments and then give labels for each segment.
For the shape one, in the control attributes we set that it has four segments and then give labels for each segment.
We drag out a Navigation bar and place it at the top of the screen and we draw out a toolbar and place it at the bottom of the screen.
We delete the button on the latter and then draw our two segmented controls to the appropriate bars.
Finally, we hook-up the segmented control IBOutlet of the file's owner to the color segmented control; and we hook up the valueChanged methods of the two segmented controls to the appropriate shapeChanged or colorChanged of the file's owners.

Using Locations and the Accelerometer

We will build an iPhone app with three labels: one with the current location, one with the current heading, and one accelerometer info.
To start we make a new view-based application.
We make sure to add to the list of frameworks the CoreLocation.framework.
If you don't do this, in the linking phase of your project you will get mysterious undefined symbols.

SensorTestsViewController.h

The header file for our sensor text project basically imports CoreLocations and sets up the outlets and properties of our three labels.

Notice we promise that our controller has methods

- (void) locationManager: (CLLocationManager *)manager 
	didUpdateToLocation: (CLLocation *)newLocation fromLocation: (CLLocation *)oldLocation ;

- (void) locationManager:(CLLocationManager *)manager 
		didUpdateHeading: (CLHeading *)newHeading ;

- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error ;

to handle location and heading info, we implement the interface CLLocationManagerDelegate

#import <UIKit/UIKit.h>
#import <CoreLocation/CoreLocation.h>
#import <CoreMotion/CoreMotion.h>

@interface SensorTestsViewController : UIViewController <CLLocationManagerDelegate> 
@property (weak, nonatomic) IBOutlet UILabel *locationLabel;
@property (weak, nonatomic) IBOutlet UILabel *headingLabel;
@property (weak, nonatomic) IBOutlet UILabel *accelerometerLabel;
@property (strong, nonatomic) CLLocationManager *locationManager;
@property (strong, nonatomic) CMMotionManager *motionManager;
@property (strong, nonatomic) NSOperationQueue *queue;


@end

SensorTestsViewController.xib

We add three labels and play with their colors so that the UI of our app looks like:
I also changed the line breaks property for the label data to character wraps.
Finally, I control dragged from File's Owner to each of the labels to hook up the outlets.

SensorTestsViewController.m

Here is our implementation file:

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void) viewDidLoad {
    [super viewDidLoad];
    _locationManager = [[CLLocationManager alloc] init];

    _locationManager.delegate = self;

    _locationManager.desiredAccuracy = kCLLocationAccuracyBest;

    [_locationManager startUpdatingLocation];
    [_locationManager startUpdatingHeading];

    _motionManager = [[CMMotionManager alloc] init];
    if(_motionManager.accelerometerAvailable) {
        _motionManager.accelerometerUpdateInterval = 1.0/10.0;/* how many times a second to send
                                                              acclerometer updates. Shouldn't do too fast or battery dies. */
        [_motionManager startAccelerometerUpdatesToQueue:_queue withHandler:
        ^(CMAccelerometerData *accelerometerData, NSError *error) {
            NSString *labelText;
            if(error) {
                [_motionManager stopAccelerometerUpdates];
                labelText = [NSString stringWithFormat:@"Accelerometer encountered error %@", error];
            } else {
                labelText = [NSString stringWithFormat:@"Accelerometer\n--\n"
                             "x: %+.2f\ny:%+.2f\nz:%+.2f",
                             accelerometerData.acceleration.x,
                             accelerometerData.acceleration.y,
                             accelerometerData.acceleration.z];
            }
            dispatch_async(dispatch_get_main_queue(), ^{
                _accelerometerLabel.text = labelText;
            });
        }];
    } else {
        _accelerometerLabel.text = @"This Device has no accelerometer";
    }
}

- (void) locationManager: (CLLocationManager *)manager
     didUpdateToLocation: (CLLocation *)newLocation fromLocation: (CLLocation *)oldLocation {


    NSString *loc = [[NSString alloc] initWithFormat:@"My Coordinates: %@",
                     newLocation.description];
    _locationLabel.text = loc;

}

- (void) locationManager:(CLLocationManager *)manager
        didUpdateHeading: (CLHeading *)newHeading {

    NSString *head = [[NSString alloc] initWithFormat:@"My Heading: %@",
                      newHeading.description];
    _headingLabel.text = head;
}

- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error {
    if ([error code] == kCLErrorDenied) {
        [_locationManager stopUpdatingLocation];
    }
}


@end

Remarks

If you look at the code, in viewDidLoad I start the locationManager to send update events of the location and heading to the current heading. If this were a better app I would maybe have a toggle that sent the stopUpdatingLocation and stopUpdatingHeading messages to the locationManager at some point.
In the CLLocationManagerDelegate methods we implement above I only use the description property of CLLocation and CLHeading. This is a nice handy dandy string summarizing the information that these classes provide; however, it is not necessarily the most convenient thing for other applications.
CLLocation has altitude, coordinate, course, speed, horizontalAccuracy, and verticalAccuracy properties from which more information can be more directly had.
For example, coordinate is a CLLocationCoordinate2D object which is a struct with two members longitude and latitude which give these values in degrees.
Similarly, CLHeading has properties headingAccuracy (max deviation degrees), magneticHeading, timestamp, trueHeading, x, y, and z.
x, y, and z are values between -128, and +128 and represent the deviation from the magnetic field lines about the vertical length of the phone, the horizontal length of the phone, and through the height of the phone.
The accelerometer's x, y, z attributes measure the acceleration of the device in the horizontalwise, lengthwise, and height directions

Sensor App Running

Here is a screenshot of the sensor app running, this is an example of app which is better to test on an actual device:

Android Sensor's Revisited

We have already talked about how to use the LocationManager in Android.
To make an app that uses the Accelerometer, you should use the SensorManager class.
We will make a simple app to write the current accelerometer info in a TextView.

To begin here is what our apps only layout and string.xml file look like:

string.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="xyz">Acceleration: X: Y: Z:</string>
    <string name="app_name">AccelerometerDemo</string>
</resources>

main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/xyz"
    android:id="@+id/acceleration"
    />
</LinearLayout>

AcceleratorDemo.java

We use onCreate to set up the SensorManager and to get a Sensor object for our accelerometer.
We use onResume to register a listener for SensorEvents from the accelerometer.
We use onPause to remove this listener.
Our activity itself implements SensorEventListener and to do this it needs to implement:
```
    public void onSensorChanged(SensorEvent event);
    public void onAccuracyChanged(Sensor arg0, int arg1);
```
We really only care about code in the former method.
The SensorEvent object we get has a values array which gives us the x, y, z directions of acceleration.

Here is the final code for AcceleratorDemo.java:

package org.pollett;

import java.util.List;

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

public class AccelerometerDemo extends Activity implements SensorEventListener 
{
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) 
    {
    	
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        accelerationLabel = (TextView )this.findViewById(R.id.acceleration);        

        manager = (SensorManager)getSystemService(SENSOR_SERVICE);
        List<Sensor> list = manager.getSensorList(Sensor.TYPE_ACCELEROMETER);
        if(list != null && list.size() > 0) {
            accelerometer = list.get(0);
        }

    }

    @Override
    public void onResume() 
    {
    	super.onResume();
    	if(accelerometer != null) 
    	{
            manager.registerListener(this, 
                accelerometer, SensorManager.SENSOR_DELAY_NORMAL);
    	}

    }
 
    @Override
    public void onPause() 
    {
    	super.onPause();
        if(accelerometer != null) 
    	{
    		manager.unregisterListener(this);
    	}  

    }
    
    public void onAccuracyChanged(Sensor arg0, int arg1) {

    }

    public void onSensorChanged(SensorEvent event) {
       accelerationLabel.setText("Acceleration X:" + event.values[0]
          + " Y:" + event.values[1]
          + " Z:" + event.values[2]);		
    }
    
    protected TextView accelerationLabel;
    protected SensorManager manager;
    protected Sensor accelerometer;    

}

Graphics iPhone; Sensors

Outline

Introduction