Angular-Docs-Cn/modules/angular2/src/directives/switch.js

import {Decorator} from 'angular2/src/core/annotations_impl/annotations';
import {ViewContainerRef} from 'angular2/src/core/compiler/view_container_ref';
import {ProtoViewRef} from 'angular2/src/core/compiler/view_ref';
import {isPresent, isBlank, normalizeBlank} from 'angular2/src/facade/lang';
import {ListWrapper, List, MapWrapper, Map} from 'angular2/src/facade/collection';
import {Parent} from 'angular2/src/core/annotations_impl/visibility';

class SwitchView {
  _viewContainerRef: ViewContainerRef;
  _protoViewRef: ProtoViewRef;

  constructor(viewContainerRef: ViewContainerRef, protoViewRef: ProtoViewRef) {
    this._protoViewRef = protoViewRef;
    this._viewContainerRef = viewContainerRef;
  }

  create() {
    this._viewContainerRef.create(this._protoViewRef);
  }

  destroy() {
    this._viewContainerRef.clear();
  }
}

/**
 * The `Switch` directive is used to conditionally swap DOM structure on your template based on a
 * scope expression.
 * Elements within `Switch` but without `SwitchWhen` or `SwitchDefault` directives will be
 * preserved at the location as specified in the template.
 *
 * `Switch` simply chooses nested elements and makes them visible based on which element matches
 * the value obtained from the evaluated expression. In other words, you define a container element
 * (where you place the directive), place an expression on the **`[switch]="..."` attribute**),
 * define any inner elements inside of the directive and place a `[switch-when]` attribute per
 * element.
 * The when attribute is used to inform Switch which element to display when the expression is
 * evaluated. If a matching expression is not found via a when attribute then an element with the
 * default attribute is displayed.
 *
 * # Example:
 *
 * ```
 * <ANY [switch]="expression">
 *   <template [switch-when]="whenExpression1">...</template>
 *   <template [switch-when]="whenExpression1">...</template>
 *   <template [switch-default]>...</template>
 * </ANY>
 * ```
 *
 * @exportedAs angular2/directives
 */
@Decorator({
  selector: '[switch]',
  properties: {
    'value': 'switch'
  }
})
export class Switch {
  _switchValue: any;
  _useDefault: boolean;
  _valueViews: Map;
  _activeViews: List<SwitchView>;

  constructor() {
    this._valueViews = MapWrapper.create();
    this._activeViews = ListWrapper.create();
    this._useDefault = false;
  }

  set value(value) {
    // Empty the currently active ViewContainers
    this._emptyAllActiveViews();

    // Add the ViewContainers matching the value (with a fallback to default)
    this._useDefault = false;
    var views = MapWrapper.get(this._valueViews, value);
    if (isBlank(views)) {
      this._useDefault = true;
      views = normalizeBlank(MapWrapper.get(this._valueViews, _whenDefault));
    }
    this._activateViews(views);

    this._switchValue = value;
  }

  _onWhenValueChanged(oldWhen, newWhen, view: SwitchView):void {
    this._deregisterView(oldWhen, view);
    this._registerView(newWhen, view);

    if (oldWhen === this._switchValue) {
      view.destroy();
      ListWrapper.remove(this._activeViews, view);
    } else if (newWhen === this._switchValue) {
      if (this._useDefault) {
        this._useDefault = false;
        this._emptyAllActiveViews();
      }
      view.create();
      ListWrapper.push(this._activeViews, view);
    }

    // Switch to default when there is no more active ViewContainers
    if (this._activeViews.length === 0 && !this._useDefault) {
      this._useDefault = true;
      this._activateViews(MapWrapper.get(this._valueViews, _whenDefault));
    }
  }

  _emptyAllActiveViews():void {
    var activeContainers = this._activeViews;
    for (var i = 0; i < activeContainers.length; i++) {
      activeContainers[i].destroy();
    }
    this._activeViews = ListWrapper.create();
  }

  _activateViews(views: List<SwitchView>):void {
    // TODO(vicb): assert(this._activeViews.length === 0);
    if (isPresent(views)) {
      for (var i = 0; i < views.length; i++) {
        views[i].create();
      }
      this._activeViews = views;
    }
  }

  _registerView(value, view: SwitchView): void {
    var views = MapWrapper.get(this._valueViews, value);
    if (isBlank(views)) {
      views = ListWrapper.create();
      MapWrapper.set(this._valueViews, value, views);
    }
    ListWrapper.push(views, view);
  }

  _deregisterView(value, view: SwitchView):void {
    // `_whenDefault` is used a marker for non-registered whens
    if (value == _whenDefault) return;
    var views = MapWrapper.get(this._valueViews, value);
    if (views.length == 1) {
      MapWrapper.delete(this._valueViews, value);
    } else {
      ListWrapper.remove(views, view);
    }
  }
}


/**
 * Defines a case statement as an expression.
 *
 * If multiple `SwitchWhen` match the `Switch` value, all of them are displayed.
 *
 * Example:
 *
 * ```
 * // match against a context variable
 * <template [switch-when]="contextVariable">...</template>
 *
 * // match against a constant string
 * <template [switch-when]="'stringValue'">...</template>
 * ```
 *
 * @exportedAs angular2/directives
 */
@Decorator({
  selector: '[switch-when]',
  properties: {
    'when' : 'switch-when'
  }
})
export class SwitchWhen {
  _value: any;
  _switch: Switch;
  _view: SwitchView;

  constructor(viewContainer: ViewContainerRef, protoViewRef: ProtoViewRef, @Parent() sswitch: Switch) {
    // `_whenDefault` is used as a marker for a not yet initialized value
    this._value = _whenDefault;
    this._switch = sswitch;
    this._view = new SwitchView(viewContainer, protoViewRef);
  }

  onDestroy() {
    this._switch
  }

  set when(value) {
    this._switch._onWhenValueChanged(this._value, value, this._view);
    this._value = value;
  }
}


/**
 * Defines a default case statement.
 *
 * Default case statements are displayed when no `SwitchWhen` match the `switch` value.
 *
 * Example:
 *
 * ```
 * <template [switch-default]>...</template>
 * ```
 *
 * @exportedAs angular2/directives
 */
@Decorator({
  selector: '[switch-default]'
})
export class SwitchDefault {
  constructor(viewContainer: ViewContainerRef, protoViewRef: ProtoViewRef, @Parent() sswitch: Switch) {
    sswitch._registerView(_whenDefault, new SwitchView(viewContainer, protoViewRef));
  }
}

var _whenDefault = new Object();