问题描述
下面的类继承自 Textarea 小部件，并具有javascript代码，显示用户可以在文本区域中输入多少个字符。
The below class inherits from the Textarea widget and features javascript code that displays how many characters more a user can enter in a textarea.
class TextAreaWithCharCounter(forms.Textarea):
class Media:
js = ('js/jquery.charcounter.js',)
def render(self, name, value, attrs = None):
id = attrs['id']
max_length = self.attrs.get('max_length', 200)
output = super(TextAreaWithCharCounter, self).render(name, value, attrs)
output += mark_safe(u'''
<script type="text/javascript">
$("#%s").charCounter(%d, {classname:"charcounter"});
</script>'''%(id, max_length))
return output
表单的相关部分代码如下：
The relevant portion of the form code is as follows:
class MyForm(forms.Form):
foo = forms.CharField(max_length = 200, widget = TextAreaWithCharCounter(attrs={'max_length':200}))
...
ÿ ou可以看到我传递了 max_length 参数两次，一个用于该字段，一个用于小部件。更好的方法可能是从窗口小部件内部访问窗体字段，并获取其max_length属性，以便窗口小部件不需要max_length参数。如何做到这一点？
You can see that I pass the max_length argument twice, one for the field and one for the widget. A better way may be accessing the form field from inside the widget and get its max_length attribute, so that a max_length argument won't be required by the widget. How can I do that?
推荐答案
从技术上讲，Widget不一定要直接关系到Field你不这样做。
Technically, a Widget doesn't have to have a direct relationship back to a Field, so you don't do this.
查看，你可以看到它有一个 widget_attrs 方法自动将 maxlength 属性添加到 TextInput / PasswordInput 字段。
Looking at the source of CharField, you can see that it has a widget_attrs method which automatically adds the maxlength attribute to TextInput / PasswordInput fields.
我建议您使用自定义字段来覆盖此方法，并为自定义Widget添加一个属性。
I suggest you use a custom Field which overrides this method and adds an attribute for your custom Widget.
此外，我不确定将它留在 attrs 是一个好主意，无论如何 - < TextArea> 将以无效的 max_length 参数呈现。也许你应该是 pop（）取而代之？
Also, I'm not sure that leaving it in attrs is a good idea anyway - the <TextArea> will be rendered with an invalid max_length argument. Perhaps you should be pop()ing it off instead?
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