<li ng-class="{true:'z_step_bar_active',false:'z_step-bar'}[file.step=='2'||file.step=='3']"></li>
当model file.step的值为2时或者3时class为z_step_bar_active否则为z_step_bar
<li ng-class="{true:'z_step_bar_active',false:'z_step-bar'}[file.step=='2'||file.step=='3']"></li>
当model file.step的值为2时或者3时class为z_step_bar_active否则为z_step_bar