Basics of iOS

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-(void) spinnerStart
{
[self spinnerEnd];

spinnerViewWhole=[[UIView alloc]initWithFrame:CGRectMake(0,0,self.window.frame.size.width,self.window.frame.size.height)];
spinnerViewWhole.backgroundColor=[UIColor colorWithWhite:0 alpha:0.8];
[self.window addSubview:spinnerViewWhole];


aSpinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];

[aSpinner setFrame:CGRectMake(self.window.frame.size.width/2-20,self.window.frame.size.height/2-20, 40, 40)];

[self.window addSubview: aSpinner];

[aSpinner startAnimating];

}
-(void) spinnerEnd
{
[aSpinner stopAnimating];

if(spinnerViewWhole)
{
[spinnerViewWhole removeFromSuperview];

}

if(aSpinner)
{
[aSpinner removeFromSuperview];

}

}
Paste this code in Appdelegate and use spinner in entire project