\n Android app development is receiving more attention than ever. In particular, Google’s Jetpack library is a powerful tool that makes the development of Android applications easier and more efficient. In this course, we will take a closer look at how to create screens based on Jetpack using Java.\n <\/p>\n
\n Jetpack is a set of numerous libraries and architecture components for Android development that helps make app development, testing, and maintenance easier and faster. Jetpack is composed of the following key components.\n <\/p>\n
\n Let’s learn how to set up a project using Jetpack with Android Studio. Please follow the steps below.\n <\/p>\n
dependencies {\n implementation 'androidx.appcompat:appcompat:1.3.0'\n implementation 'androidx.activity:activity-ktx:1.2.3'\n implementation 'androidx.lifecycle:lifecycle-runtime-ktx:2.4.0'\n implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.4.0'\n}<\/code><\/pre>\n<\/li>\n- \n Sync the Gradle file.\n <\/li>\n<\/ol>\n
3. Creating the Basic Screen<\/h2>\n
\n Now let’s write the XML layout and Java code to create the basic screen.\n <\/p>\n
3.1 Creating the XML Layout File<\/h3>\n
\n Open the project\u2019s res\/layout\/activity_main.xml<\/code> file and modify it as follows.\n <\/p>\n<?xml version=\"1.0\" encoding=\"utf-8\"?>\n<RelativeLayout xmlns:android=\"http:\/\/schemas.android.com\/apk\/res\/android\"\n android:layout_width=\"match_parent\"\n android:layout_height=\"match_parent\">\n\n <TextView\n android:id=\"@+id\/text_view\"\n android:layout_width=\"wrap_content\"\n android:layout_height=\"wrap_content\"\n android:text=\"Hello, Jetpack!\"\n android:textSize=\"24sp\"\n android:layout_centerInParent=\"true\" \/>\n\n <Button\n android:id=\"@+id\/button\"\n android:layout_width=\"wrap_content\"\n android:layout_height=\"wrap_content\"\n android:text=\"Click Me\"\n android:layout_below=\"@id\/text_view\"\n android:layout_centerHorizontal=\"true\"\n android:layout_marginTop=\"20dp\" \/>\n\n<\/RelativeLayout><\/code><\/pre>\n3.2 Writing MainActivity.java<\/h3>\n
\nOpen the MainActivity.java<\/code> file and write the code as follows. This code implements the functionality to change the text upon button click.\n <\/p>\npackage com.example.myapplication;\n\nimport android.os.Bundle;\nimport android.view.View;\nimport android.widget.Button;\nimport android.widget.TextView;\n\nimport androidx.appcompat.app.AppCompatActivity;\n\npublic class MainActivity extends AppCompatActivity {\n private TextView textView;\n private Button button;\n\n @Override\n protected void onCreate(Bundle savedInstanceState) {\n super.onCreate(savedInstanceState);\n setContentView(R.layout.activity_main);\n\n textView = findViewById(R.id.text_view);\n button = findViewById(R.id.button);\n\n button.setOnClickListener(new View.OnClickListener() {\n @Override\n public void onClick(View v) {\n textView.setText(\"Button Clicked!\");\n }\n });\n }\n}<\/code><\/pre>\n4. Utilizing ViewModel and LiveData<\/h2>\n
\n Using Jetpack’s ViewModel and LiveData allows for efficient management of UI data. ViewModel retains UI-related data, and LiveData automatically updates the UI upon data changes.\n <\/p>\n
4.1 Creating the ViewModel Class<\/h3>\n
\n Create a new class to implement ViewModel. Create a MyViewModel.java<\/code> file and enter the following code.\n <\/p>\npackage com.example.myapplication;\n\nimport androidx.lifecycle.LiveData;\nimport androidx.lifecycle.MutableLiveData;\nimport androidx.lifecycle.ViewModel;\n\npublic class MyViewModel extends ViewModel {\n private final MutableLiveData text = new MutableLiveData<>();\n\n public MyViewModel() {\n text.setValue(\"Hello, Jetpack with ViewModel!\");\n }\n\n public LiveData getText() {\n return text;\n }\n\n public void updateText(String newText) {\n text.setValue(newText);\n }\n}<\/code><\/pre>\n4.2 Using ViewModel in MainActivity<\/h3>\n
\n Now let’s use the ViewModel in MainActivity to update the text. Modify the code as follows.\n <\/p>\n
package com.example.myapplication;\n\nimport android.os.Bundle;\nimport android.view.View;\nimport android.widget.Button;\nimport android.widget.TextView;\n\nimport androidx.appcompat.app.AppCompatActivity;\nimport androidx.lifecycle.Observer;\nimport androidx.lifecycle.ViewModelProvider;\n\npublic class MainActivity extends AppCompatActivity {\n private MyViewModel myViewModel;\n\n @Override\n protected void onCreate(Bundle savedInstanceState) {\n super.onCreate(savedInstanceState);\n setContentView(R.layout.activity_main);\n\n myViewModel = new ViewModelProvider(this).get(MyViewModel.class);\n TextView textView = findViewById(R.id.text_view);\n Button button = findViewById(R.id.button);\n\n myViewModel.getText().observe(this, new Observer() {\n @Override\n public void onChanged(String s) {\n textView.setText(s);\n }\n });\n\n button.setOnClickListener(new View.OnClickListener() {\n @Override\n public void onClick(View v) {\n myViewModel.updateText(\"Button Clicked!\");\n }\n });\n }\n}<\/code><\/pre>\n5. Screen Transitions via Navigation<\/h2>\n
\n The Jetpack Navigation component allows for easy transitions between various screens of the app. Let’s learn how to switch screens using Navigation components.\n <\/p>\n
5.1 Creating a Navigation Graph<\/h3>\n
\n Create a new Navigation graph file. Create a res\/navigation\/nav_graph.xml<\/code> file and set it up as follows.\n <\/p>\n<?xml version=\"1.0\" encoding=\"utf-8\"?>\n<navigation xmlns:android=\"http:\/\/schemas.android.com\/apk\/res\/android\"\n xmlns:app=\"http:\/\/schemas.android.com\/apk\/res-auto\"\n xmlns:tools=\"http:\/\/schemas.android.com\/tools\"\n app:startDestination=\"@id\/firstFragment\">\n\n <fragment\n android:id=\"@+id\/firstFragment\"\n android:name=\"com.example.myapplication.FirstFragment\"\n android:label=\"First Fragment\"\n tools:layout=\"@layout\/fragment_first\">\n <\/fragment>\n\n <fragment\n android:id=\"@+id\/secondFragment\"\n android:name=\"com.example.myapplication.SecondFragment\"\n android:label=\"Second Fragment\"\n tools:layout=\"@layout\/fragment_second\">\n <\/fragment>\n\n<\/navigation><\/code><\/pre>\n5.2 Creating Fragment Classes<\/h3>\n
\n To implement navigation, we will add two Fragment classes. First, create FirstFragment.java<\/code>.\n <\/p>\npackage com.example.myapplication;\n\nimport android.os.Bundle;\nimport android.view.LayoutInflater;\nimport android.view.View;\nimport android.view.ViewGroup;\n\nimport androidx.fragment.app.Fragment;\n\npublic class FirstFragment extends Fragment {\n @Override\n public View onCreateView(LayoutInflater inflater, ViewGroup container,\n Bundle savedInstanceState) {\n return inflater.inflate(R.layout.fragment_first, container, false);\n }\n}<\/code><\/pre>\n\n Next, create the SecondFragment.java<\/code> file.\n <\/p>\npackage com.example.myapplication;\n\nimport android.os.Bundle;\nimport android.view.LayoutInflater;\nimport android.view.View;\nimport android.view.ViewGroup;\n\nimport androidx.fragment.app.Fragment;\n\npublic class SecondFragment extends Fragment {\n @Override\n public View onCreateView(LayoutInflater inflater, ViewGroup container,\n Bundle savedInstanceState) {\n return inflater.inflate(R.layout.fragment_second, container, false);\n }\n}<\/code><\/pre>\n6. Conclusion<\/h2>\n
\n Developing Android apps utilizing Jetpack allows for efficient use of various features such as UI components, data management, and fragment navigation. In this course, we configured a basic screen using Java and implemented state management using ViewModel and LiveData. We also learned how to facilitate screen transitions easily using navigation components.\n <\/p>\n
\n To develop more complex apps, you can leverage additional components and libraries, and enhance code reusability and maintainability through the various features of Jetpack. Keep practicing and try applying it to actual projects to gain more experience.\n <\/p>\n
References<\/h2>\n