Question

如何在运营商链中订阅之前检查条件？我有类似的东西。

onDropdownChange(event:Event)
{
   this.parentElem = event.value === 'parent';
}

此函数更改属性值。

<select (change)="onDropdownChange($event)">
 ...
</select>

html元素

.takeWhile(...)

已经尝试使用.skipWhile(...)＆amp; #include <iostream> class Box { public: double l, w, h; double vol, surf; double getVol() { return l*w*h; }; double getSurf() { return (l*w + l*h + w*h) * 2; }; double getVolDiff() { boxTemp->l = l + 1; boxTemp->w = w; boxTemp->h = h; return getVol() - boxTemp->getVol(); }; static Box* getInstance() { if (_instance == 0) { _instance = new Box; } return _instance; } void setTemp(Box *b1) { boxTemp = b1; } private: Box* boxTemp; static Box *_instance; }; Box* Box::_instance = 0; int main(int argc, const char * argv[]) { Box box; box.l = 1; box.w = 2; box.h = 3; std::cout << "Vol: " << box.getVol() << std::endl; std::cout << "Surf: " << box.getSurf() << std::endl; Box *orj = Box::getInstance(); orj->l = 4; orj->w = 5; orj->h = 6; std::cout << "*** Vol: " << box.getVol() << std::endl; std::cout << "*** Surf: " << box.getSurf() << std::endl; orj->setTemp(&box); std::cout << "Vol Diff: " << orj->getVolDiff() << std::endl; return 0;但我不知道它是否适用于我的病情。

Answer 1

通过这样做解决了。

this.myForm.get('grandParent').valueChanges
           .filter(() => this.parentElem && ...more conditions) // only execute further chain if true;
           .map(val => {

                    this.$parent.empty();
                    return this.dropdownProvider.getParent(val);

         }).subscribe(service => service.subscribe(data => {

              data = data.map(d => { return { id: d.text, text: d.text };   });
              this.initParent(data);

        }));

如果条件满足则订阅，否则返回/退出rxjs

1 个答案: