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ASP.NET MVC:Why does the CheckBoxFor render an additional input tag and how can I get the value using the FormCollection
I needed to create a check box and bind the model to the check box. Assume instead of the model value im just assigning false as the value. Code given bellow.
#Html.CheckBox("abcd",false)
Output:
<input id="abcd" name="abcd" type="checkbox" value="true" />
<input name="abcd" type="hidden" value="false" />
The output of the HTML being generated is shown above. I do understand why the hidden check box is put by the razor view engine. My question is if the value is false then the check box visible should be value="false" (unchecked).
Why it has put value="true" (checked). Same applies for the checkboxfor helper. What is wrong or could you explain how to implement this?
You should consider passing the value via the model:
#Html.CheckBoxFor(model => model.abcd)
If you need to set it to be 'false' then you can do this by setting the abcd property to false in the Controller before returning the View.
Checkboxes don't have different checked/unchecked values, they only have a checked value. If you understand why razor outputs the hidden field then you understand this.
Imagine for a second that it did have value='false'. What would happen when you checked the checkbox? Would you expect the value to change? (hint: you shouldn't). You'd have a checked checkbox with value='false'. What does that even mean? Then, upon posting, you would post false as your value, and that would be nonsense.
So. Checkbox value attributes don't change. If you need to write code that uses the value, don't look for its value, look for whether or not it's checked.
Related
This has confused me since the early days. Maybe it's just in my head, but it seems to me as if this has varied over time, between browsers, and possibly even depending on the local language/locale.
Basically, whenever I need to check if a HTML input of type "radio" or "checkbox" has been set, I always do:
if (isset($_POST['the_name']) && trim($_POST['the_name']))
// do stuff
This just makes sure that the POST variable is sent whatsoever (which in itself doesn't mean that it was actually checked/selected, as far as I can tell, since its "value" can be an empty string) and that it's something other than '' (empty string). It seems like this has worked for a long time, but I have two problems with it:
It's ugly. I need to abstract it into a function, but then I want to know if it's a good idea in the first place, or wrong somehow.
It makes the assumption that any non-empty string value means "checked" or "selected", whereas the standard may say a specific string value such as "on", or maybe any number of such strings depending on the language/locale.
Are there cases where my above code falls apart? Do browsers ever submit POST forms where they include names which have no user input/selection in the HTTP request? Or does the existence of a name in the POST blob mean that that "field" has been actively changed/set/checked/selected?
The idea behind checkboxes is that the value is sent over to the server only if the checkbox was checked when submitting the form. The value can be anything, even an empty string. As long as the field is part of the transmitted form it means the box was ticked.
The value attribute is one which all <input>s share; however, it serves a special purpose for inputs of type checkbox: when a form is submitted, only checkboxes which are currently checked are submitted to the server, and the reported value is the value of the value attribute. If the value is not otherwise specified, it is the string on by default.
This means you could have a form like this:
<form action="" method="get">
<input type="checkbox" name="c1" value="">
<input type="submit" value="Send">
</form>
If the checkbox is not checked when submitting then $_GET will be an empty array.
If the checkbox is checked then the value of $_GET will be:
array('c1' => '');
To check whether the box was ticked when sending the form you only need isset()
if (isset($_POST['c1']) {
// The box was checked!
}
Sometimes you would like to assign a value attribute to your checkbox. In such situations you can use the shorthand operator for isset() function ??.
// Create a variable from the checkbox value or assign an empty string if the box was not checked
$nyCheckbox = $_POST['c1'] ?? '';
I have an edit page where several fields are conditionally disabled, based on the user's role. When the fields are disabled, their values are not posted to the server (as expected), which causes the ModelState to be invalid, as the values are required.
To get around this, I want to add Html.HiddenFor() for the fields; so that a value will still get posted (and so that it will retain those values if the View is returned). However, in the case that those fields are not disabled, I will then have both a TextBoxFor and a HiddenFor going to the same model property.
I have run a couple tests, and it appears that when this happens, the value of the first element on the form will be binded to the model, while the next one just gets ignored. If this is the case, then I should be able to just put the HiddenFor after the TextBoxFor, in which case the value of the hidden input will only be posted when the regular input is disabled.
#Html.TextBoxFor(m => m.FirstName)
#Html.HiddenFor(m => m.FirstName) #*Only gets binded to the model if the above text box is disabled*#
(There is some JavaScript that conditionally disabled the visible TextBox).
So two questions: 1) Is it documented that MVC binding will always work this way; can I safely have both of these fields?
And, 2) Is there a better approach to accomplishing this? I know that I can but the HiddenFor inside an #If statement so that it will only get created if the TextBox is disabled; but that is a lot of extra logic in the View that I'd like to avoid.
The DefaultModelBinder reads the values from the request in order and binds the first matching name/value pair and ignores subsequent matches (unless the property is IEnumerable). This is how the CheckBoxFor() method ensures a true or false value is always submitted to the controller (the method generates a checkbox with value="True" and a hidden input with value="False"), so you can safely add the hidden input after the textbox.
One option you might consider rather than a disabled textbox, is to make it readonly, which means it will always submit a value, therefore you only need one input (and you can always style it to look disabled if that is what you want).
Have a look at the following screenshot. You can see that the text input field is empty, yet its value attribute is set to "b".
You'll also notice in the Properties tab, under input, that value here is set to "". Why are they different? What does this mean?
Could this be related to the fact that the input was rendered by React?
If it helps, here is the jsx responsible for this element (redacted):
return (
<td
key={field._id}
className={`oldField ${colPos}`}
>
<input
type="text"
defaultValue={value}
onChange={this.changeOldField(record, field)}
/>
</td>
)
It seems that you are changing the defaultValue based on something from the state. The defaultValue prop should be set only once and not changed later on, because any more changes will be ignored by React. If you want to change the value based on state you should use the normal value prop. Otherwise, if you want a predefined value to appear to the user and at the same time control the input when it gets changed, you can either use some logic in your code that handles both onChange and the code in your component that wants to automatically change the value, or possibly place it in the placeholder prop, which will give you something like what you want.
I'm having trouble with Laravel's Form::model() construct. I was able to populate it with my model data but the checkboxes aren't being checked. The values are being set to 1 or 0 (courtesy of Eloquent calling a "boolean" a "tinyint" in MySQL), but I can't see how to use the Form::model() approach and set that checked attribute if the value coming is an integer and not a boolean (hence why I think Form Model Binding for checkboxes isn't working).
I'm specifying this in my view:
{{ Form::checkbox('hasDiscount') }}
And the form builder is returning this:
<input name="hasDiscount" type="checkbox" value="1" id="hasDiscount">
I think it's not really related to data-value. The value could be 'true' and the checked attribute could be false as well.
If you want to display checkbox with checked attribute, you can try my wait (it's not the best, I admit):
Form::model($model)
Form::checkbox('name', null, $model->value)
Form::close()
The third parameter could be convert to false if the value of model is null or 0 and the checkbox is not checked. otherwise, it's checked.
If you have another idea, please share it.
I am using the djFilteringSelect control to show values in a dropdown as user type a value.
The lookup and typehead is working fine. The user type a letter and the dropdown allow the user to select a value which is then displayed in the dropdown field.
If the user now decide to remove the value first selected so that the combobox is empty and leave the field, then the first value in the list is now automatically filled in.
The consequence of this is that if the user have added a value there is no way to remove the value and leave the box emtpy.
I am using required=false for both the control and the dojo attribute but it does not seem to help. There are also a few other djFilteringSelect attributes I have tried like "Autocomplete" and "trim" but it does not work
Here is the code
<xe:djFilteringSelect id="test" type="select" store="jsondata" searchAttr="data" required="false" labelType="html" invalidMessage="Not valid">
<xe:this.dojoAttributes>
<xp:dojoAttribute name="required" value="false"></xp:dojoAttribute>
</xe:this.dojoAttributes>
</xe:djFilteringSelect>
Initally the field is not required, but if the user have entered a value it is required.
My question is if there a way to prevent the djFilteringSelect control to always populate the field if I have previously added a value
I found someone who solved this in another stack overflow topic, by creating an empty entry in my data store. but I could not get this to work
Dojo: Select of empty value for FilteringSelect while required=false
I do this quite a lot. Right now I don't have a working sample to show you (since I moved to bootstrap - and have to code the selects by manually adding select2 controls) but something like this should do it...
I add an "empty" value at the top of my select - and that seems to work no matter whether I am using a combobox, djCombobox or combobox with select2 from bootstrap. My markup typically looks like:
<xp:comboBox id="inputLocationSelector" value="#{User.catchListType}" disableClientSideValidation="true">
<xp:selectItem itemLabel="(none)" itemValue=""></xp:selectItem>
<xp:selectItems>
<xp:this.value><![CDATA[${Configuration.meta.listLocationTypeOptions}]]></xp:this.value>
</xp:selectItems>
</xp:comboBox>
Then you could specify "(none)", "All" or " " for the "not-selected" value depending on your needs.
Validation is a different thing so just specifying "required=false" does not give you the "empty" value.
/John