fixture.detectChange開始單步調試，如何執行到Directive的ngOnChange鈎子

is._tick裡調用this.changeDetectorRef.detectChanges():

首先從RootViewRef開始檢測：

context裡能看到Component的資料：

renderComponentOrTemplate:

refreshView裡會調用init和check hook:

/**
 * Executes post-order init and check hooks (one of AfterContentInit, AfterContentChecked,
 * AfterViewInit, AfterViewChecked) given a view where there are pending init hooks to be executed.
 * @param lView The LView where hooks are defined
 * @param hooks Hooks to be run
 * @param initPhase A phase for which hooks should be run
 * @param nodeIndex 3 cases depending on the value:
 * - undefined: all hooks from the array should be executed (post-order case)
 * - null: execute hooks only from the saved index until the end of the array (pre-order case, when
 * flushing the remaining hooks)
 * - number: execute hooks only from the saved index until that node index exclusive (pre-order
 * case, when executing select(number))
 */
function executeInitAndCheckHooks(lView, hooks, initPhase, nodeIndex) {
    ngDevMode &&
        assertNotEqual(initPhase, 3 /* InitPhaseCompleted */, 'Init pre-order hooks should not be called more than once');
    if ((lView[FLAGS] & 3 /* InitPhaseStateMask */) === initPhase) {
        callHooks(lView, hooks, initPhase, nodeIndex);
    }
}
      

使用Directive執行個體調用hook：

function rememberChangeHistoryAndInvokeOnChangesHook() {
    const simpleChangesStore = getSimpleChangesStore(this);
    const current = simpleChangesStore === null || simpleChangesStore === void 0 ? void 0 : simpleChangesStore.current;
    if (current) {
        const previous = simpleChangesStore.previous;
        if (previous === EMPTY_OBJ) {
            simpleChangesStore.previous = current;
        }
        else {
            // New changes are copied to the previous store, so that we don't lose history for inputs
            // which were not changed this time
            for (let key in current) {
                previous[key] = current[key];
            }
        }
        simpleChangesStore.current = null;
        this.ngOnChanges(current);
    }
}
      

ngOnChanged hook被調用的前提是，從getSimpleChangesStore傳回的simpleChangesStore裡的current字段不為空：