Detect Retina Display

#define IS_RETINA ([[UIScreen mainScreen] respondsToSelector:@selector(displayLinkWithTarget:selector:)] && ([UIScreen mainScreen].scale == 2.0))

if(IS_RETINA)
{
   // Retina display
} else {
  // non-Retina display

}

Full Screen Dialog

final Dialog instructionDialog = new Dialog(getParent(), android.R.style.Theme);
instructionDialog.getWindow().requestFeature(Window.FEATURE_NO_TITLE);
instructionDialog.setContentView(getLayoutInflater().inflate(R.layout.dialog_instruction
       , null));
instructionDialog.getWindow().setLayout(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
Button btn = (Button) instructionDialog.findViewById(R.id.btn_instruction);
btn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
instructionDialog.dismiss();
}
});
instructionDialog.show();

Make a UIImage from a MKMapView or Other View

The improved function for retina display:


- (UIImage*) renderToImage
{
    if(UIGraphicsBeginImageContextWithOptions != NULL)
    {
        UIGraphicsBeginImageContextWithOptions(mapView.frame.size, NO, 0.0);
    } else {
        UIGraphicsBeginImageContext(mapView.frame.size);
    }
    [mapView.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext(); 
    return image;
}