title: Change image of UIButton on select or unselect
body: <p>I want in my iOS app user can select some field on clicking the <code>UIButton</code>.</p>
  
  <p>I want when user selects the field on click of <code>UIButton</code>,image of button should change and open my <code>MMPickerView</code> and when user clicks again the <code>UIButton</code> should get unselected and display previous image in <code>UIButton</code> and do not open <code>MMPickerview</code> at this time.</p>
  
  <p>This is my code:</p>
  
  <pre><code> - (IBAction)showPickerViewButtonPressed:(id)sender {
        if( (_button.selected = !_button.selected))
        {
             UIImage *bimage=[UIImage imageNamed: @"play.jpg"];
             [_button setImage:bimage forState:UIControlStateNormal];
        } 
        else
        {
             [MMPickerView showPickerViewInView:self.view
                         withStrings:_stringsArray
                         withOptions:@{MMbackgroundColor: [UIColor blackColor],
                                       MMtextColor: [UIColor whiteColor],
                                       MMtoolbarColor: [UIColor blackColor],
                                       MMbuttonColor: [UIColor whiteColor],
                                       MMfont: [UIFont systemFontOfSize:18],
                                       MMvalueY: @3,
                                       MMselectedObject:_selectedString}
                          completion:^(NSString *selectedString) {
  
                              _label.text = selectedString;
                              _selectedString = selectedString;
               }];
           }
     }
  </code></pre>