4.1 依赖性注入
令牌 构建 依赖
Injector Provider Object 难。。

4.2 changeDetection
检查变化的策略：默认：全局检查,
改为onpush策略，减少全局检查的频率，大应用可以以此提高性能
(changeDetection:ChangeDetectionStrategy.OnPush)
然后在constructor中申明ChangeDetectorRef，再调用它的markDetector方法

constructor(...,private cd:ChangeDetectorRef )
xx(){
    ...
    this.cd,markForCheck();
}

4.3 指令
指令：组件是一种带模板的指令
指令分为结构型（Structural）指令和属性型（Attribute）指令

Renderer2 和 ElementRef
Angular不提倡直接操作DOM，这是一个危险的行为
对于DOM的操作应该通过Renderer2来进行，ElementRef可以理解为指向DOM元素的引用

drag-drop 拖拽 Can't bind to 'app-draggable' since it isn't a known property of 'mat-list-item'. 1. If 'mat-list-item' is an Angular component and it has 'app-draggable' input,then verify that it is part of this module. 2. If 'mat-list-item' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message. 3. To allow any property add 'NO_ERRORS_SCHEMA' to the '@NgModule.schemas' of this component. (" 'priority-emergency':item.priority===1 }" [ERROR ->][app-draggable]="true" [draggedClass]="drag-start" (click)="onItemClick()" "): ng:///TaskModule/TaskItemComponent.html@7:2 --->莫名其妙 多保存几次就好了 [app-draggable]="true" [draggedClass]="'drag-start'" 不加''会认为是成员变量，找不到就是undefined