How to assign value to class in angular 5?

Question

I have angular class

export class Parameters
{
SearchString:string;
}

I have code in component.ts file

strparameters:Parameters;
ngOnInit() {
this.strparameters.SearchString="";
this.dataservice.getEmployee(this.strparameters).subscribe((tempdate) =>{
this.employeelist=tempdate;
})
,err=>{
console.log(err);
}
}

it gives me error -

 

ERROR TypeError: Cannot set property 'SearchString' of undefined

how can assign input value to SearchString in component.ts file ? please help here