There are 2 ways to handle the click event in button
- Onclick in xml layout
- Using an OnClickListener
Onclick in XML layout
When the user clicks a button, the Button object receives an on-click event.
To make click event work add
android:onClick attribute to the Button element in your XML layout. The value for this attribute must be the name of the method you want to call in response to a click event. The Activity hosting the layout must then implement the corresponding method.
If you use this event handler in your code, make sure that you are having that button in your MainActivity. It won’t work if you use this event handler in fragment because onClick attribute only works in Activity or MainActivity.
In MainActivity class
Make sure that your sendMessage method should have the following :
Using an OnClickListener
You can also declare the click event handler programmatically rather than in an XML layout. This event handler code is mostly preferred because it can be used in both Activities and Fragments.
There are two ways to do this event handler programmatically :
- Implementing View.OnClickListener in your Activity or fragment.
- Creating new anonymous View.OnClickListener.
Implementing View.OnClickListener in your Activity or fragment
View.OnClickListener in your Activity or Fragment, you have to override
onClick method on your class.
Firstly, link the button in xml layout to java by calling
R.id.button_send refers the button in XML.
mButton.setOnClickListener(this); means that you want to assign listener for your Button “on this instance” this instance represents
OnClickListener and for this reason your class have to implement that interface.
If you have more than one button click event, you can use switch case to identify which button is clicked.
Creating Anonymous View.OnClickListener
Link the button from the XML by calling
findViewById() method and set the onClick listener by using
setOnClickListener takes an
OnClickListener object as the parameter. Basically it’s creating an anonymous subclass OnClickListener in the parameter.
It’s like the same in java when you can create a new thread with an anonymous subclass.