Have you ever get irritated by the unlimited number of findViewById method calls and complex on-click-listeners? Obviously, they increase the complexity of the code and they consume more time as well. Butter Knife is a perfect solution to get out of these irritating and time-consuming code segments.
Butter Knife is an injection library used to inject views into Java classes. Using this library is not going to reduce the performance since it uses compile-time injection instead of runtime injection. Compared to some other Android libraries and frameworks, it is less featured but personally, I like this library a lot for its less configuration and high performance. This article introduces the basic functionalities of Butter Knife and more details can be found at the official website.
Let's create a simple application with a TextBox and a Button to demonstrate the application of Butter Knife.
Step 1:Create a new Android project “Butter Knife Demo”.
Step 2:
Create a TextBox and a Button in the activity_main.xml.
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/etName"
android:hint="Enter your name..."
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="183dp" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="OK"
android:id="@+id/btnOK"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="121dp" />
</RelativeLayout>Step 3:
Add the Butter Knife dependency to the build.gradle (Module:app).
compile 'com.jakewharton:butterknife:6.1.0'After the modification, the build.gradle must look like this.
apply plugin: 'com.android.application'
android {
compileSdkVersion 21
buildToolsVersion "21.1.2"
defaultConfig {
applicationId "com.javahelps.butterknifedemo"
minSdkVersion 10
targetSdkVersion 22
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
compile fileTree(include: ['*.jar'], dir: 'libs')
compile 'com.android.support:appcompat-v7:22.1.1'
compile 'com.jakewharton:butterknife:6.1.0'
}After saving this file, synchronize the Gradle build.
Step 4:
Add an instance variable for EditText in the MainActivity.java. This instance variable should not be private or static if you are willing to inject it using Butter Knife.
package com.javahelps.butterknifedemo;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.widget.EditText;
public class MainActivity extends ActionBarActivity {
EditText etName;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}Annotate the instance variable using @InjectView(int) annotation as shown below.
package com.javahelps.butterknifedemo;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.widget.EditText;
import butterknife.InjectView;
public class MainActivity extends ActionBarActivity {
@InjectView(R.id.etName)
EditText etName;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}Step 6:
Create a method for on click as shown below.
public void showName() {
String name = etName.getText().toString();
Toast.makeText(this, name, Toast.LENGTH_SHORT).show();
}Step 7:
Annotate the method using @OnClick annotation to bind it with the button click.
@OnClick(R.id.btnOK)
public void showName() {
String name = etName.getText().toString();
Toast.makeText(this, name, Toast.LENGTH_SHORT).show();
}Step 8:
Finally, call the 'inject(Activity)' method of ButterKnife class from the onCreate method.
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.inject(this);
}The final source code should be something similar to this code:
package com.javahelps.butterknifedemo;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.widget.EditText;
import android.widget.Toast;
import butterknife.ButterKnife;
import butterknife.InjectView;
import butterknife.OnClick;
public class MainActivity extends ActionBarActivity {
@InjectView(R.id.etName)
EditText etName;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.inject(this);
}
@OnClick(R.id.btnOK)
public void showName() {
String name = etName.getText().toString();
Toast.makeText(this, name, Toast.LENGTH_SHORT).show();
}
}Here you can see that there are no findViewById method calls and no on-click listeners. The code looks pretty simple and easy to read.
Step 9:
Save all the changes and run the application.
Find the project at Git Hub.
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