ExtJS 监听器：匿名函数参数

发布于 2024-09-12 17:09:20 字数 518 浏览 6 评论 0原文

我从互联网上遇到的某本书中获取了这段代码...

sm: new Ext.grid.RowSelectionModel({
   singleSelect: true,
   listeners: {
       rowselect: {
           fn: function(sm,index,record) {
               Ext.Msg.alert('You Selected',record.data.title);
           }
       }
   }
});

现在，sm 是选择模型的简写，我们在这里讨论 ExtJS GridPanel...一切都很清楚，直到 <代码>fn：部分。 AFAIK，匿名函数传递 3 个参数：sm、index 和 record。

现在我即将因为问一些极其琐碎的问题而投票：你如何知道应该传递哪些参数？如果我省略索引参数，我会收到错误...为什么我必须传递3个参数？有什么问题吗？

原文

I grabbed this code form some book I've bumped on the InternetS...

sm: new Ext.grid.RowSelectionModel({
   singleSelect: true,
   listeners: {
       rowselect: {
           fn: function(sm,index,record) {
               Ext.Msg.alert('You Selected',record.data.title);
           }
       }
   }
});

now, sm is shorthand for selection model, we're discussing a ExtJS GridPanel here... Everything is clear until the fn: part. AFAIK, an anonymous function is passed with 3 parameters: sm, index, and record.

Right now I'm about to get down votes for asking something extremely trivial: how do you know which parameters you should pass? If I omit index parameter, I'll get an error... Why do I must pass 3 parameters? What's the catch?

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通知家属抬走 2024-09-19 17:09:20

考虑这种情况：

//called with (selectionModelInstance, Index, Record)
function myCallback(sm,index,record) {
  //Parameter mapping:
  //sm -> selectionModelInstance
  //index -> Index
  //record -> Record
  alert(record.data);
  //record is actually a record object, so record.data works
}

观察跳过参数时会发生什么：

//called with (selectionModelInstance, Index, Record)
function myCallback(sm,record) {
  //Parameter mapping:
  //sm -> selectionModelInstance
  //record -> Index
  alert(record.data); //Error
  //record is actually Index here, and it obviosly doesn't have data property.
}

您看到的错误与调用函数时参数不匹配无关。 Javascript 允许使用任意数量的参数调用任何带有任意数量参数的函数。该错误与尝试取消引用不存在的属性 record.data 有关。

为了回答你的问题，你必须使用API指定的签名来定义回调函数，只是为了正确映射参数。

Consider this scenario:

//called with (selectionModelInstance, Index, Record)
function myCallback(sm,index,record) {
  //Parameter mapping:
  //sm -> selectionModelInstance
  //index -> Index
  //record -> Record
  alert(record.data);
  //record is actually a record object, so record.data works
}

Watch what happens when you skip a parameter:

//called with (selectionModelInstance, Index, Record)
function myCallback(sm,record) {
  //Parameter mapping:
  //sm -> selectionModelInstance
  //record -> Index
  alert(record.data); //Error
  //record is actually Index here, and it obviosly doesn't have data property.
}

The error that you seeing has nothing to do with parameter mismatch when calling a function. Javascript allows any function taking any number of parameters to be called with any number of parameters. The error is to do with trying to dereference the property record.data which is not there.

To answer you question, you must define the callback function using the signature specified by the API, simply for the sake of parameters being mapped correctly.

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