为什么这个angular2代码失败了

Question

                        <select class="form-control" #platformFilter >
                                <option value="">Select</option>
                                <option value="PC">PC</option>
                                <option value="PS3">PS3</option>
                                <option value="PS4">PS4</option>
                                <option value="XBox">XBox</option>
                                <option value="XB1">XB1</option>
                            </select>



                        <select class="form-control" #gameFilter >
                                <option value="">Select</option>
                                <option value="World of WarCraft">World of WarCraft</option>
                                <option value="Left 4 Dead 2">L4D2</option>
                                <option value="Diablo 3">Diablo 3</option>
                                <option value="Destiny">Destiny</option>
                            </select>



                        <input type="datetime-local" class="form-control" #timeFilter >


                        <button class="btn btn-primary" (click)="applyFilter(platformFilter.value, gameFilter.value, timeFilter.value)">Apply filter</button>



applyFilter(platform:string = null, game:string = null, time:string = null) {
    console.log("why?");
}

我不确定我的代码会发生什么 错误是

  

错误类型错误：无法读取未定义的属性“值”   Object.eval [as handleEvent]（GroupingComponent.html：231）

那发生了什么？

---------------------------------------编辑：抱歉，包含的细节较少，这是我的完整代码

Answer 1

为什么它是参数平台：string = null， 尝试将其更改为，

applyFilter(platform: string) {
    console.log("why?");
}

Answer 2

似乎有效，

   <select #selectedCategory>
     <option value="PC">PC</option>
      <option value="PS3">PS3</option>
    </select>
    <button (click)="getValueFromSelect(selectedCategory.value)">click</button>  

`

<强> DEMO

Answer 3

以下三个对象似乎是null，检查你的打字稿代码。

• platformFilter
• gameFilter
• timeFilter

<button class="btn btn-primary" (click)="applyFilter(platformFilter.value, gameFilter.value, timeFilter.value)">Apply filter</button>