Component template文件源代码：
<button [disabled]="isDisabled" >Click me</button>
Component实现：
export class AppComponent implements OnInit {
counter = 0;
get isDisabled(){
console.log('Jerry: ' + this.counter++);
return true;
}
}
Component里维护了一个计数器：counter
运行时的输出：
下面是分别研究这四次get调用的上下文。
第一次触发
通过_loadComponent触发：
第二次触发
同第一次触发一样，同样是在tick方法里，只不过第一次触发在tick的view.detectChanges里，而第二次触发，在view.checkNoChanges里：
/**
* Invoke this method to explicitly process change detection and its side-effects.
*
* In development mode, `tick()` also performs a second change detection cycle to ensure that no
* further changes are detected. If additional changes are picked up during this second cycle,
* bindings in the app have side-effects that cannot be resolved in a single change detection
* pass.
* In this case, Angular throws an error, since an Angular application can only have one change
* detection pass during which all change detection must complete.
* @return {?}
*/
第三次触发
class ApplicationRef {
/**
* \@internal
* @param {?} _zone
* @param {?} _console
* @param {?} _injector
* @param {?} _exceptionHandler
* @param {?} _componentFactoryResolver
* @param {?} _initStatus
*/
constructor(_zone, _console, _injector, _exceptionHandler, _componentFactoryResolver, _initStatus) {
this._zone = _zone;
this._console = _console;
this._injector = _injector;
this._exceptionHandler = _exceptionHandler;
this._componentFactoryResolver = _componentFactoryResolver;
this._initStatus = _initStatus;
/**
* \@internal
*/
this._bootstrapListeners = [];
this._views = [];
this._runningTick = false;
this._enforceNoNewChanges = false;
this._stable = true;
/**
* Get a list of component types registered to this application.
* This list is populated even before the component is created.
*/
this.componentTypes = [];
/**
* Get a list of components registered to this application.
*/
this.components = [];
this._enforceNoNewChanges = isDevMode();
this._zone.onMicrotaskEmpty.subscribe({
next: (/**
* @return {?}
*/
() => {
this._zone.run((/**
* @return {?}
*/
() => {
this.tick();
}));
})
});
第四次也是最后一次触发
更多Jerry的原创文章，尽在：“汪子熙”: