通過fragment模擬一個微信主頁面 

• 在佈局中宣告UI

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height
 
="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <LinearLayout
        android:id="@+id/ll"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:orientation="horizontal" />

    <
 
LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/btn1"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight
 
="1"
            android:text="微信" />

        <Button
            android:id="@+id/btn2"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="通訊錄" />

        <Button
            android:id="@+id/btn3"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="發現" />

        <Button
            android:id="@+id/btn4"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="我" />
    </LinearLayout>
</LinearLayout>

• 宣告四個fragment,每個fragmen分別代表一個頁面 
• 根據UI寫對應邏輯

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        LinearLayout ll = findViewById(R.id.ll);
        Button btn1 = findViewById(R.id.btn1);
        Button btn2 = findViewById(R.id.btn2);
        Button btn3 = findViewById(R.id.btn3);
        Button btn4 = findViewById(R.id.btn4);
        btn1.setOnClickListener(this);
        btn2.setOnClickListener(this);
        btn3.setOnClickListener(this);
        btn4.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        FragmentManager fm = getSupportFragmentManager();
        FragmentTransaction ft = fm.beginTransaction();
        switch (v.getId()) {
            case R.id.btn1:
                ft.replace(R.id.ll, new MessageFragment());
                break;
            case R.id.btn2:
                ft.replace(R.id.ll, new ContactFragment());
                break;
            case R.id.btn3:
                ft.replace(R.id.ll, new DiscoverFragment());
                break;
            case R.id.btn4:
                ft.replace(R.id.ll, new MimeFragment());
                break;
        }
        ft.commit();
    }
}