实现标题栏联动Fragment

效果图：

首先实现布局文件的代码，代码中的colorBlue颜色代码"#039BE5"，其他的不多说了，直接上代码：

<?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">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@color/colorBlue">

        <ImageButton
            android:id="@+id/btn_Img_Ret"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerVertical="true"
            android:layout_marginLeft="10dp"
            android:background="#0000"
            android:scaleType="fitXY"
            android:src="@mipmap/ret_left_white" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerHorizontal="true"
            android:layout_centerVertical="true"
            android:text="事件管理"
            android:textColor="#FFFFFF"
            android:textSize="18sp"
            android:textStyle="bold" />
    </RelativeLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:gravity="center_vertical"
        android:orientation="horizontal">

        <TextView
            android:id="@+id/txt1"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:gravity="center"
            android:text="六一"
            android:textSize="14sp" />

        <TextView
            android:id="@+id/txt2"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:gravity="center"
            android:text="国庆"
            android:textSize="14sp" />

        <TextView
            android:id="@+id/txt3"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:gravity="center"
            android:text="中秋"
            android:textSize="14sp" />
    </LinearLayout>

    <View
        android:layout_width="match_parent"
        android:layout_height="1dp"
        android:background="@color/colorBlue" />

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/viewPage"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

然后新建fragment，我这里是3个，每个fragment的代码都是一样的，fragment和布局文件就贴一个就行了：

public class TestFragment1 extends Fragment {

    private View view;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        view = inflater.inflate(R.layout.fragment_test1,null);

        return view;
    }
}

布局文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:gravity="center"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView
        android:text="六一"
        android:textSize="30sp"
        android:textStyle="bold"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

建立好3个fragment和布局文件后就开始我们的fragment的适配器：

public class FragmentAdapter extends FragmentPagerAdapter {

    private List<Fragment> fragmentList;

    public FragmentAdapter (FragmentManager fm,List<Fragment> list){
        super(fm);
        this.fragmentList = list;
    }

    @NonNull
    @Override
    public Fragment getItem(int position) {
        //显示第几个页面
        return fragmentList.get(position);
    }

    @Override
    public int getCount() {
        return fragmentList.size();
    }
}

最后就是实现代码了，直接上代码：

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    //第一次点击与第二次点击的间隔时间
    private long exitTime;

    private List<Fragment> fragmentList;
    private ViewPager viewPager;
    private FragmentAdapter adapter;
    private ImageButton btnImg;
    private TextView textView1,textView2,textView3;
    private int num = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
    }

    private void initView(){
        btnImg = (ImageButton)findViewById(R.id.btn_Img_Ret);
        textView1 = (TextView)findViewById(R.id.txt1);
        textView2 = (TextView)findViewById(R.id.txt2);
        textView3 = (TextView)findViewById(R.id.txt3);

        textView1.setOnClickListener(this);
        textView2.setOnClickListener(this);
        textView3.setOnClickListener(this);
        btnImg.setOnClickListener(this);

        viewPager = (ViewPager)findViewById(R.id.viewPage);
        viewPager.setOnPageChangeListener(new MyPagerChangeListener());

        fragmentList = new ArrayList<>();
        fragmentList.add(new TestFragment1());
        fragmentList.add(new TestFragment2());
        fragmentList.add(new TestFragment3());

        adapter = new FragmentAdapter(getSupportFragmentManager(),fragmentList);
        viewPager.setAdapter(adapter);

        //初始化显示第一个页面,以及更改选中的标题样式
        viewPager.setCurrentItem(0); //选中第一个页面
        textView1.setTextSize(16); //设置选中的标题字体16sp
        textView1.setTextColor(Color.parseColor("#039BE5")); //设置选中的标题字体颜色
    }


    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.txt1:
                viewPager.setCurrentItem(0);
                break;
            case R.id.txt2:
                viewPager.setCurrentItem(1);
                break;
            case R.id.txt3:
                viewPager.setCurrentItem(2);
                break;
        }
    }

    //设置一个ViewPager的监听事件，当左右滑动ViewPager时菜单栏被选中状态跟着改变
    public class MyPagerChangeListener implements ViewPager.OnPageChangeListener{

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }

        @Override
        public void onPageSelected(int position) {
            switch (position){
                case 0:
                    textView1.setTextSize(16);
                    textView2.setTextSize(14);
                    textView3.setTextSize(14);
                    textView1.setTextColor(Color.parseColor("#039BE5"));
                    textView2.setTextColor(Color.GRAY);
                    textView3.setTextColor(Color.GRAY);
                    break;
                case 1:
                    textView1.setTextSize(14);
                    textView2.setTextSize(16);
                    textView3.setTextSize(14);
                    textView1.setTextColor(Color.GRAY);
                    textView2.setTextColor(Color.parseColor("#039BE5"));
                    textView3.setTextColor(Color.GRAY);
                    break;
                case 2:
                    textView1.setTextSize(14);
                    textView2.setTextSize(14);
                    textView3.setTextSize(16);
                    textView1.setTextColor(Color.GRAY);
                    textView2.setTextColor(Color.GRAY);
                    textView3.setTextColor(Color.parseColor("#039BE5"));
                    break;
            }
        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    }

    /**
     * 实现点击两次系统返回键退出应用
     * @param keyCode
     * @param event
     * @return
     */
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if(keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0){
            exit();
            return true;
        }
        return super.onKeyDown(keyCode, event);
    }

    private void exit(){
        if((System.currentTimeMillis() - exitTime) > 2000){
            Toast.makeText(this, "再次点击退出应用", Toast.LENGTH_SHORT).show();
            exitTime = System.currentTimeMillis();
        }else{
            finish();
            System.exit(0);
        }
    }
}