Category Archives: Droid SDK

Using the Droid SDK and tips and tricks which can help you avoid SDK pitfalls that Droid has.

Drawing with the Canvas object in Android

When writing an Android game one of the first things I had to start looking at is the methods provided for drawing. Being that I had no real purpose for developing a 3D game, I decided to go 2D. There are many things that a bitmap can do for you in regards to saving you development time, but the game platform that I am pursuing next did much better with mathematical drawing.

This brought me to searching out the object that I would use to display colorful shapes that I chose at specific window positions. The first object I have come across to do this is the Canvas. A Canvas can be accessed by overriding the OnDraw method of the Android View object. A View is an object that you place in your layout to indicate UI functionality. While there are many methods in the Canvas that work well for drawing, I focused in on two of them which were drawLine and drawRectangle.

In my example I went through a few iterations to figure out screen width and what I should do with it, but ultimately I started focusing in on using a percentage of the screen with as opposed to using hard coded numbers, as it scales better on landscape mode if you go back and forth between portrait. Ultimately I came up with a method that looks like this to draw a block on my game:

GamePieceBlock block = m_BoardBlocks.get(i);
blockLeftSide = leftSide + (width / m_PiecesWide) * block.getXPosition();
blockRightSide = blockLeftSide + (width / m_PiecesWide);
Paint pnt = new Paint();

blockBottomSide = bottomSide - (height / m_PiecesTall) * block.getYPosition();
blockTopSide = blockBottomSide - (height / m_PiecesTall);

m_Canvas.drawRect(blockLeftSide, blockTopSide, blockRightSide, blockBottomSide, pnt);

This method draws a solid block of color at the position that I calculated.  To get the m_Canvas instance I set it in my onDraw method and then call down to my game methods to draw the object on the canvas.  The other method that I use is the drawLine method which looks like this:

m_Canvas.drawLine(rightSide, bottomSide, rightSide, topSide, boardPaint);
m_Canvas.drawLine(rightSide + 1, bottomSide, rightSide + 1, topSide, boardPaint);

HOW TO: Get A Date From A DatePicker

If you are writing an Android application, you likely have come across some form of the DatePicker object. This object exposes a UI that allows a phone user to pick a month, day and year. Unfortunately, the object itself does not expose any methods to turn this into a date object. Unlike similar controls across other languages, you must construct the date object yourself. While this does cause burden, you can also create your own DatePicker class and implement this method if you prefer. To do this, you can create the following method to return back a date object:

public Date getDate() {
    	return new Date(this.getYear() + 1900, this.getMonth(), this.getDayOfMonth());

Otherwise, you will have to create a new date object every time you want to fetch this information from the DatePicker. Cheers!