Custom view example

gistfile1.java

public class ShapeView extends View {

	private final static String tag = ShapeView.class.getSimpleName();
	private final int DEFAULT_SIZE_DP = 100;

	private int measuredWidth;
	private int measuredHeight;

	private Shape shapeType;
	private int color;

	private Paint paint = new Paint();
	private Rect rect = new Rect(0,0,0,0);

	private int centerX;
	private int centerY;
	private int radius;

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

	public ShapeView(Context context, AttributeSet attrs) {
		this(context, attrs, 0);
	}

	public ShapeView(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs);

		TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.ShapeView, defStyle, 0);

		color = a.getColor(R.styleable.ShapeView_shapeColor, Color.WHITE);

		paint = new Paint();
		paint.setColor(color);
		paint.setStyle(Style.FILL_AND_STROKE);
		paint.setAntiAlias(true);

		shapeType = Shape.getShapeByCode(a.getInt(R.styleable.ShapeView_shapeType, Shape.SQUARE.getCode()));

		a.recycle();
	}

	@Override
	public void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		canvas.save();
		if (shapeType == Shape.SQUARE) {
			canvas.drawRect(rect, paint);
		} else {
			canvas.drawCircle(centerX, centerY, radius, paint);
		}
		canvas.restore();
	}
	
	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		measuredWidth = measure(widthMeasureSpec);
		measuredHeight = measure(heightMeasureSpec);
		setMeasuredDimension(measuredWidth, measuredHeight);
		refreshContent();
	}

	private int measure(int measureSpec) {
		int mode = MeasureSpec.getMode(measureSpec);
		int size = MeasureSpec.getSize(measureSpec);

		float density = getResources().getDisplayMetrics().density;

		if (mode == MeasureSpec.UNSPECIFIED) {
			Log.i(tag, "measure - unspecified, size - " + size);
			return (int) (DEFAULT_SIZE_DP * density);
		} else if (mode == MeasureSpec.EXACTLY) { 
			Log.i(tag, "measure - exactly, size - " + size);
			return size;
		} else {
			Log.i(tag, "measure - at_most, size - " + size);
			return Math.min(size, (int) (DEFAULT_SIZE_DP * density));
		}
	}
	
	private void refreshContent() {
		if (shapeType == Shape.CIRCLE) {
			radius = Math.min(measuredWidth, measuredHeight) / 2;
			centerX = measuredWidth / 2;
			centerY = measuredHeight / 2;
		} else {
			int side = Math.min(measuredWidth, measuredHeight);
			int left = (measuredWidth - side)/2;
			int top = (measuredHeight - side)/2;
			rect = new Rect(left, top, left + side, top + side);
		}
	}

}