I realize that a similarly-worded question has been asked before, but this is different. I am pretty new at developing android apps and I have three questions regarding the difference(s) between the android:onclick="" XML attribute and the setOnClickListener method.
What are the differences between the two? Is the difference between the two implementations found at compile time or run time or both?
What use cases are favorable to which implementation?
What difference(s) does the use of fragments in Android make in implementation choice?
Difference Between OnClickListener vs OnClick:
OnClickListener is the interface you need to implement and can be set
to a view in java code.
OnClickListener is what waits for someone
to actually click, onclick determines what happens when someone
clicks.
Lately android added a xml attribute to views called android:onclick,
that can be used to handle clicks directly in the view's activity
without need to implement any interface.
You could easily swap one listener implementation with another if you need to.
An OnClickListener enable you to separate the action/behavior of the click event from the View that triggers the event. While for simple cases this is not such a big deal, for complex event handling, this could mean better readability and maintainability of the code
Since OnClickListener is an interface, the class that implements it has flexibilities in determining the instance variables and methods that it needs in order to handle the event. Again, this is not a big deal in simple cases, but for complex cases, we don't want to necessary mix up the variables/methods that related to event handling with the code of the View that triggers the event.
The onClick with function binding in XML Layout is a binding between onClick and the function that it will call. The function have to have one argument (the View) in order for onClick to function.
Both function the same way, just that one gets set through java code and the other through xml code.
setOnClickListener Code Implementation:
Button btn = (Button) findViewById(R.id.mybutton);
btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
myFancyMethod(v);
}
});
// some more code
public void myFancyMethod(View v) {
// does something very interesting
}
XML Implementation:
<?xml version="1.0" encoding="utf-8"?>
<!-- layout elements -->
<Button android:id="#+id/mybutton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Click me!"
android:onClick="myFancyMethod" />
<!-- even more layout elements -->
Performance:
Both are the same in performance. Xml is pre-parsed into binary code while compiling. so there is no over-head in Xml.
Limitation:
android:onClick is for API level 4 onwards, so if you're targeting < 1.6, then you can't use it.
I'm shocked nobody talked about this but be careful, although android:onClick XML seems to be a convenient way to handle click, the setOnClickListener implementation do something additional than adding the onClickListener. Indeed, it put the view property clickable to true.
While it's might not be a problem on most Android implementations, according to the phone constructor, button is always default to clickable = true but other constructors on some phone model might have a default clickable = false on non Button views.
So setting the XML is not enough, you have to think all the time to add android:clickable="true" on non button, and if you have a device where the default is clickable = true and you forget even once to put this XML attribute, you won't notice the problem at runtime but will get the feedback on the market when it will be in the hands of your customers !
In addition, we can never be sure about how proguard will obfuscate and rename XML attributes and class method, so not 100% safe that they will never have a bug one day.
So if you never want to have trouble and never think about it, it's better to use setOnClickListener or libraries like ButterKnife with annotation #OnClick(R.id.button)
Simply:
If you have android:onClick = "someMethod" in xml, it looks for the public void someMethod in your Activity class. OnClickListener is called right from your Activity and it is linked to some particular View. For example someButton.setOnClickListener and in the code below is said what has to be done when someButton is pressed.
Hope it helps :)
As said before: they both are a way to add logic in response to an event, in this case a 'click' event.
I would go for a separation between logic and presentation, just like we do in the HTML/JavaScript world: Leave the XML for presentation and add event listeners by means of code.
There are a couple of reasons why you might want to programmatically set an OnClickListener. The first is if you ever want to change the behaviour of your button while your app is running. You can point your button at another method entirely, or just disable the button by setting an OnClickListener that doesn't do anything.
When you define a listener using the onClick attribute, the view looks for a method with that name only in its host activity. Programmatically setting an OnClickListener allows you to control a button's behaviour from somewhere other than its host activity. This will become very relevant when we use Fragments, which are basically mini activities, allowing you to build reusable collections of views with their own lifecycle, which can then be assembled into activities. Fragments always need to use OnClickListeners to control their buttons, since they're not Activities, and won't be searched for listeners defined in onClick.
If you have several buttons using only one method, I suggest doing it in java. But if you have a button with one specific method, onClick in XML would be better.
It's more convenient to always use android:onClick attribute unless you have a good reason not to, for example, if you instantiate the Button at runtime or you need to declare the click behavior in a Fragment subclass.
I think main difference between them is:
OnClick: When you click on the button with your finger.
OnClickListner: It is may be a wider choice that be implemented in various codes.
For example when you type url "ymail.com", yahoo finds your username and your password from your browser and enable click state button to open your mail. This action should be implemented only in onClickListener.
This is my idea!
I am working on a project and I was wondering how can I implement like button(custom) in list view.
it should append likes for the particular row whenever like button is pressed and unlike it if pressed for second time.just like face book.
can anyone provide me link to such tutorial??
I also want to know how to handle back end part..
please suggest something.
thank you.
In your custom adapter's getView() you need to add a method as setOnClickListener() for the buttons you're using.
Any data associated with the button has to be added with myButton.setTag() in the getView() and can be accessed in the onClickListener via view.getTag()
I found a material design widget for android and want to implement EditText with onClick to set the text with DateDialog.
But from this issue of the lib : https://github.com/rey5137/material/issues/144
I can't figure it out, how to set onClick Listener on Material EditText. I have same issue with this lib, and based on my experiment, implementing onFocusChange is not solving the problem
The author just say the EditText component is extended from FrameLayout, and get the id with findviewbyid method.
That means the library is not that good, but to answer your question, seems he means that his widget is something like this
<FrameLayout>
<!-- something else -->
<EditText></EditText>
</FrameLayout>
when you set the onClickListener on the widget, actually you have just set the onClickListener on the FrameLayout. When you actually click the on it, the real EditText get the touch event and processed it, therefore the touch event is not passed to the FrameLayout as it has already been handled.
Its possible to have a listener to all buttons without setting the onClickListener in each button across all activities? and without making a extends button with the listener already set.
No. Each view has to be told what to listen to. You can specify it in xml if you prefer with the onClick attribute, but you'll still need to specify it on each object.
If all the buttons are doing the exact same thing, you can include that in the List kind of a layout and have one button with just one onCLick() event
I have a short question. Should I use in same time OnTouch and OnClick listeners ?
If I`m correct one is for touch screens and other is for devices with out it. Am I wrong ? If not should I use both listeners to secure both kind of devices ?
You only need OnTouch if you have some event that should only happen with a touch screen. If you just want to do something when the user taps (or clicks), then you only need OnClick.
I use both. I've create a class extending from Button class. I've put my custom appearance and interaction (programmaticaly) on the onTouch() method and the functionality for the onClick().