Ionic3 / Angular2 view render multiple time

问题:

I created a new ionic 3 project. In my HomePage, i have only one varible and one function:

count = 0;
printLog() {
    console.log("count", ++this.count);
}

In template home.html i call this function by interpolation binding:

{{printLog()}}

It is my whole code. In the console i see the log:

As we can see the printLog function were called 9 times. I can't understand why. Can someone tell me why and how does it work?
Many thanks!