为什么这个angular2代码的失败

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?"); 
} 

我不知道我的代码 发生什么事，误差

ERROR TypeError: Cannot read property 'value' of undefined at Object.eval [as handleEvent] (GroupingComponent.html:231)

到底发生了什么？

---------------------------------------编辑：对不起，包含较少的细节，这是我的全部代码

Answer 1

为什么它的参数平台：字符串=空， 尝试改变它，

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

Answer 2

这似乎是工作，

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

`

DEMO

Answer 3

看来下面三个对象是null，请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>