angular - ngOnChanges 跟踪以前的值和新值？

Question

在我的 angular 项目中，我试图通过点击下一个/上一个按钮来浏览列表。我有一个复选框，可以将显示的小时数从几小时更改为几天。我希望能够通过员工来回走动，并使值(value)观正确。有人告诉我，这可以通过 ngOnChanges 并跟踪以前的和新的值来完成。

这就是我所拥有的，它正在更改新值，但是我将如何更改以前的值？

 ngOnChanges(changes: { [propName: string]: SimpleChange }) {
    for (let propName in changes) {
        if (propName == "selectedEmployee") {
            if (this.timeVar == "days") {
                this.empInfo[this.selectedEmployee].STDLTD = this.empInfo[this.selectedEmployee].STDLTD * 8;
                this.empInfo[this.selectedEmployee].Uncharged = this.empInfo[this.selectedEmployee].Uncharged * 8;

                this.empInfo[this.selectedEmployee].PTOBase = this.empInfo[this.selectedEmployee].PTOBase * 8;
                this.empInfo[this.selectedEmployee].PTOCarry = this.empInfo[this.selectedEmployee].PTOCarry * 8;
                this.empInfo[this.selectedEmployee].PTOBorrowed = this.empInfo[this.selectedEmployee].PTOBorrowed * 8;
                this.empInfo[this.selectedEmployee].PTOBalance = this.empInfo[this.selectedEmployee].PTOBalance * 8;
                this.empInfo[this.selectedEmployee].PTORequests = this.empInfo[this.selectedEmployee].PTORequests * 8;
                this.empInfo[this.selectedEmployee].PTORemaining = this.empInfo[this.selectedEmployee].PTORemaining * 8;

                this.empInfo[this.selectedEmployee].ETOEarned = this.empInfo[this.selectedEmployee].ETOEarned * 8;
                this.empInfo[this.selectedEmployee].ETORequests = this.empInfo[this.selectedEmployee].ETORequests * 8;
                this.empInfo[this.selectedEmployee].ETORemaining = this.empInfo[this.selectedEmployee].ETORemaining * 8;  
            }
        }
    }
}

Answer 1

来自 angular documentation :

ngOnChanges(changes: SimpleChanges) {
  for (let propName in changes) {
    let chng = changes[propName];
    let cur  = JSON.stringify(chng.currentValue);
    let prev = JSON.stringify(chng.previousValue);
  }
}

所以，你需要 .currentValue和 .previousValue属性来访问当前和以前的值。