Add to Friends in Views

the view will render the link regardless the permission, you must display the field by adding the field "Flag frined links" (Something like that) and you'll get the add/remove link with permissions.

i dont know if there's theme preprocess or hook code that allows you to set permission check on specific field.

the only thing i know about permissions views is that you can set entire view to require specific permission, or specific role , e.g.

authenticated user can view the view

but for specific field.. i dont know, i need more search, try first searching for a module that does that, than try for a php snippet.

If you look at the view provided (display flagged), you will see that it uses the field handler straight from Flag for this -- Flags: Flag link -- This handler checks to see if a user has permission to flag and displays accordingly.

Also, using views in the way you describe above is not a good way to go about this. Closing issue due to lack of activity.

I'm using a sidebar where information about the user being viewed is shown.
It contains also the relationship to this user with links to add or remove the relationship.

Here's how I've solved this with Views:

$view = new view;
$view->name = 'user_relationship';
$view->description = 'Provides a Block with user relationship operations';
$view->tag = 'flag.friend';
$view->view_php = '';
$view->base_table = 'users';
$view->is_cacheable = FALSE;
$view->api_version = 2;
$view->disabled = FALSE; /* Edit this to true to make a default view disabled initially */
$handler = $view->new_display('default', 'Standards', 'default');
$handler->override_option('relationships', array(
  'flag_content_rel' => array(
    'label' => 'flag',
    'required' => 0,
    'flag' => 'friend',
    'user_scope' => 'any',
    'id' => 'flag_content_rel',
    'table' => 'users',
    'field' => 'flag_content_rel',
    'override' => array(
      'button' => 'override',
    ),
    'relationship' => 'none',
  ),
));
$handler->override_option('fields', array(
  'uid' => array(
    'label' => 'Flag friend links',
    'alter' => array(
      'alter_text' => 0,
      'text' => '',
      'make_link' => 0,
      'path' => '',
      'link_class' => '',
      'alt' => '',
      'prefix' => '',
      'suffix' => '',
      'target' => '',
      'help' => '',
      'trim' => 0,
      'max_length' => '',
      'word_boundary' => 1,
      'ellipsis' => 1,
      'strip_tags' => 0,
      'html' => 0,
    ),
    'empty' => '',
    'hide_empty' => 0,
    'empty_zero' => 0,
    'exclude' => 1,
    'id' => 'uid',
    'table' => 'flag_friend',
    'field' => 'uid',
    'relationship' => 'none',
  ),
  'ops' => array(
    'label' => '',
    'alter' => array(
      'alter_text' => 0,
      'text' => '',
      'make_link' => 0,
      'path' => '',
      'link_class' => '',
      'alt' => '',
      'prefix' => '',
      'suffix' => '',
      'target' => '',
      'help' => '',
      'trim' => 0,
      'max_length' => '',
      'word_boundary' => 1,
      'ellipsis' => 1,
      'strip_tags' => 0,
      'html' => 0,
    ),
    'empty' => '',
    'hide_empty' => 0,
    'empty_zero' => 0,
    'link_type' => '',
    'exclude' => 1,
    'id' => 'ops',
    'table' => 'flag_content',
    'field' => 'ops',
    'relationship' => 'flag_content_rel',
    'override' => array(
      'button' => 'override',
    ),
  ),
  'name' => array(
    'label' => '',
    'alter' => array(
      'alter_text' => 1,
      'text' => '%1\'s [ops][uid]',
      'make_link' => 0,
      'path' => '',
      'link_class' => '',
      'alt' => '',
      'prefix' => '',
      'suffix' => '',
      'target' => '',
      'help' => '',
      'trim' => 0,
      'max_length' => '',
      'word_boundary' => 1,
      'ellipsis' => 1,
      'strip_tags' => 0,
      'html' => 0,
    ),
    'empty' => '',
    'hide_empty' => 0,
    'empty_zero' => 0,
    'link_to_user' => 0,
    'overwrite_anonymous' => 0,
    'anonymous_text' => '',
    'exclude' => 0,
    'id' => 'name',
    'table' => 'users',
    'field' => 'name',
    'relationship' => 'none',
  ),
));
$handler->override_option('arguments', array(
  'uid' => array(
    'default_action' => 'default',
    'style_plugin' => 'default_summary',
    'style_options' => array(),
    'wildcard' => 'all',
    'wildcard_substitution' => 'All',
    'title' => '',
    'breadcrumb' => '',
    'default_argument_type' => 'user',
    'default_argument' => '',
    'validate_type' => 'user',
    'validate_fail' => 'not found',
    'break_phrase' => 0,
    'not' => 0,
    'id' => 'uid',
    'table' => 'users',
    'field' => 'uid',
    'validate_user_argument_type' => 'uid',
    'validate_user_roles' => array(
      '2' => 0,
      '5' => 0,
      '3' => 0,
      '4' => 0,
    ),
    'override' => array(
      'button' => 'override',
    ),
    'relationship' => 'none',
    'default_options_div_prefix' => '',
    'default_argument_user' => 1,
    'default_argument_fixed' => '',
    'default_argument_php' => '',
    'validate_argument_node_type' => array(
      'blog' => 0,
      'panel' => 0,
      'profile' => 0,
      'page' => 0,
      'story' => 0,
    ),
    'validate_argument_node_access' => 0,
    'validate_argument_nid_type' => 'nid',
    'validate_argument_vocabulary' => array(),
    'validate_argument_type' => 'tid',
    'validate_argument_transform' => 0,
    'validate_user_restrict_roles' => 0,
    'validate_argument_node_flag_name' => '*relationship*',
    'validate_argument_node_flag_test' => 'flaggable',
    'validate_argument_node_flag_id_type' => 'id',
    'validate_argument_user_flag_name' => '*relationship*',
    'validate_argument_user_flag_test' => 'flaggable',
    'validate_argument_user_flag_id_type' => 'id',
    'validate_argument_php' => '',
  ),
));
$handler->override_option('filters', array(
  'uid_current' => array(
    'operator' => '=',
    'value' => '0',
    'group' => '0',
    'exposed' => FALSE,
    'expose' => array(
      'operator' => FALSE,
      'label' => '',
    ),
    'id' => 'uid_current',
    'table' => 'users',
    'field' => 'uid_current',
    'relationship' => 'none',
  ),
));
$handler->override_option('access', array(
  'type' => 'role',
  'role' => array(
    '2' => 2,
  ),
));
$handler->override_option('cache', array(
  'type' => 'none',
));
$handler = $view->new_display('block', 'Block', 'block_1');
$handler->override_option('block_description', 'User Relationship');
$handler->override_option('block_caching', -1);

After import, you have to 'rewrite the output' of the field user:name, so that it fits to your needs.
I use: %1's [ops][uid]
That produces an output like: 'become a friend of username' or 'cancel the friendship with username' (in my language)

I don't know if this is what was expected and is helpful for you but maybe for someone else.