Drawing Image with Alternating Colors - ipad

Question

How can we draw a background pattern (to be set to UIImageView) programmatically like the following?
It has alternating colored squares like 20 x 20 pixels. I can do it with REAL Stupid and MS Visual Basic. I have never done it with iOS. If I run a search, one clue that I get is colorWithPatternImage. I used the following REAL Stupid code a few years ago. It works regardless of the dimensions of the canvas (equivalent to UIImageView).
Dim i,j As Integer
For j=0 To Ceil(CanvasX.Height/20)
For i=0 To Ceil(CanvasX.Width/20)
If i Mod 2=0 And j Mod 2=0 Then
If CField1.text="1" Then
g.ForeColor=&cCC9900
Elseif CField1.text="2" Then
g.ForeColor=&c000000
Else
g.ForeColor=&cCCCCCC
End if
Elseif i Mod 2>0 And j Mod 2>0 Then
If CField1.text="1" Then
g.ForeColor=&cCC9900
Else
g.ForeColor=&cCCCCCC
End if
Else
If CField1.text="1" Then
g.ForeColor=&cE6E6E6
Else
g.ForeColor=&cFFFFFF
End if
End if
g.FillRect i*20,j*20,20,20
Next i
Next j
Thank you for your help.

Answer 1

Approach #1: take this image:
Then set a background color by specifying a pattern image:
UIImage *bgImage = [UIImage imageNamed:#"squares"];
UIColor *bgColor = [UIColor colorWithPatternImage:bgImage];
someView.backgroundColor = bgColor;
Approach #2: use Quartz. Subclass UIView, then implement the following method:
- (void)drawRect:(CGRect)rect
{
[super drawRect:rect];
CGContextRef ctx = UIGraphicsGetCurrentContext();
NSLog(#"%#", ctx);
CGFloat ws = self.frame.size.width;
CGFloat hs = self.frame.size.height;
const int side = 10;
int nx = ws / side;
int ny = hs / side;
CGRect rects[nx / 2];
for (int i = 0; i < ny; i++) {
for (int j = 0; j < nx; j += 2) {
rects[j / 2] = CGRectMake(j * side, i * side, side, side);
}
const static CGFloat w[4] = { 1.0, 1.0, 1.0, 1.0 };
const static CGFloat g[4] = { .75, .75, .75, .75 };
if (i % 2) {
CGContextSetFillColor(ctx, g);
} else {
CGContextSetFillColor(ctx, w);
}
CGContextFillRects(ctx, rects, nx / 2);
for (int j = 1; j < nx; j += 2) {
rects[j / 2] = CGRectMake(j * side, i * side, side, side);
}
if (i % 2) {
CGContextSetFillColor(ctx, w);
} else {
CGContextSetFillColor(ctx, g);
}
CGContextFillRects(ctx, rects, nx / 2);
}
}