get value of selected <select> element in dart

问题

how i can obtain selected option of element? document.query("#id") - returns Element which hasn't value propery so i can't do:

var val = document.query("#id").value;

 

var val = (SelectElement)(document.query("#id")).value; // - "SelectElement is class and cannot be used as an expression"

how to do type conversion in dart correctly?

回答1:

In general, when dealing with any HTML element, I usually query the HTML element first:

InputElement myElement = document.query(#myInputElement);

Then use some event to capture the value contained in that element:

int val = Math.parseInt(myElement.value);

So for example, in HTML I could have an input element of type range:

<input id="mySlider" type="range" min="1000" max="10000" step="20" value="5000" />

In Dart, I would grab the value of this slider using a mouse up event:

InputElement mySlider = document.query('#mySlider');
mySlider.on.mouseUp.add((e) {
  int _val = Math.parseInt(mySlider.value);
  document.query('#status').innerHTML = "$_val";
});

Edit: In M1, you can now just use the cast operator as. If your HTML looked like this:

<p id="text">This is some text</p>

You could retrieve the text from the paragraph tag by doing this:

String str = (query('#text') as ParagraphElement).text;

回答2:

just need:

String str = document.query("#idOfSelect").value;

will be warning, but you can ignore it

回答3:

I used:

var val = int.parse(query("#id").value, onError: (_) => 1);

This prevents an exception in case query("#id").value is null and assigns a default value (1).

来源：https://stackoverflow.com/questions/10670173/get-value-of-selected-select-element-in-dart