angular - Expression has changed after it was checked -- ngClass change -

i'm not expert in angular2. know how resolve error:

inline template:0:6332 caused by: expression has changed after checked. previous value: 'btn-disabled'. current value: ''.   [ngclass]="!formvalid() ? 'btn-disabled': ''" 

what's ideas error ?

try use:

[class.btn-disabled] = "!fromvalid()" 

when use [ngclass], should return {class-name: true/false} map.

for example:

[ngclass]="{active: isactive, disabled: isdisabled}"