Handle Events with LayoutFiles, JavaObjects & ButterKnife.

Introduction

The purpose of this app is to understand and to elaborate how we can handle events using XML layout, java & with Butter Knife which is a open source library.

Handle View events in Layout File.

We handle simple events in view components, by adding an attribute in the XML layout file android:onClick="button_xml" and then calling the method in the activity public void button_xml(View view){ }. The event handler method must receive a view object as its one and only argument. That will make the method recognizable by the framework, and it will be called, when the user clicks on that button.

Handle events with Java Object.

To handle events in using java object, we have to give the unique signature using id android:id="@+id/button_java" to the button in XML layout and get its reference and pass in the ID of the button by calling Button buttonJava = findViewById(R.id.button_java); in onCreate method of an activity. Now, call the method set on click listener :

buttonJava.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
            
            }
        });

This is the second way to handle events with pure Java code. It always works, but it is a little verbose.

Handle view events with Butter Knife.

Getting references to view objects, and setting up event handlers, takes a lot of boilerplate code.

Butter knife is a popular open source library, created by a developer named Jake Wharton.

To add the ButterKnife library go to :

Gradle Scripts

build.gradle(Module:app)

In dependencies { } add these two dependencies with whatever is the most recent version.

implementation 'com.jakewharton:butterknife:8.5.1'
annotationProcessor 'com.jakewharton:butterknife-compiler:8.5.1'

Example 1 :-

Now, in Main Activity above onCreate method add this code :

 @BindView(R.id.button_butter_knife_1)
    Button button_One;

and on onCreate method :

        button_One.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
           
            }
        });

There's an even better way of setting up event handlers using butterknife.

Example 2 :-

Above onCreate method :

 @OnClick(R.id.button_butter_knife_2)
    public void butterKnife_Button2Clicked(){
       
    }

Note :- Always remember to declare this line of code ButterKnife.bind(this); while working with ButterKnife.

Thank You.