如何使用android中的微调下拉列表在视图寻呼机中显示片段？

如何解决如何使用android中的微调下拉列表在视图寻呼机中显示片段？

我想在微调项目列表上单击项目时显示一个片段。 我现在的问题是，当我单击微调器上的一项时，我的 Viewpager 上没有显示片段。 程序没有错误。只是片段没有出现。

谁能帮我解决这个问题。非常感谢！

我的代码是：

活动：

package com.hello.menu;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Spinner;

import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;
import androidx.viewpager.widget.ViewPager;

import com.hello.About;
import com.hello.Home;
import com.hello.R;


public class SpinnersFragment extends AppCompatActivity {

    ViewPager viewPager;
    Spinner spinner;
    String[] city ={"Fragment1","Fragment2"};

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.menu_spinner_fragment);
        Toolbar toolbar = findViewById(R.id.toolbar);

        toolbar.setNavigationOnClickListener(v -> onBackpressed());

        spinner = (Spinner) findViewById(R.id.spinner);
        viewPager = (ViewPager) findViewById(R.id.view_pager);


        ArrayAdapter<String> adapter = new ArrayAdapter<>(SpinnersFragment.this,R.layout.app_text_spinner,city);
        adapter.setDropDownViewResource(R.layout.support_simple_spinner_dropdown_item);
        spinner.setAdapter(adapter);
        spinner.setonItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> adapterView,View view,int i,long l) {
                switch (i) {
                    case 0:
                        getFragment (new Home());
                        break;
                    case 1:
                        getFragment (new About());
                        break;
                }
            }

            @Override
            public void onnothingSelected(AdapterView<?> parent) {

            }
        });


    }

    private void getFragment(Fragment fragment) {
        FragmentManager manager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = manager.beginTransaction();
        fragmentTransaction.replace(R.id.view_pager,fragment);
        fragmentTransaction.commit();
    }

    @Override
    public void startActivity (Intent intent) {
        super.startActivity(intent);
        overridePendingTransitionEnter();
    }

    protected void overridePendingTransitionEnter() {
        overridePendingTransition(R.anim.slide_from_right,R.anim.slide_to_left);
    }
    protected void overridePendingTransitionExit() {
        overridePendingTransition(R.anim.slide_from_left,R.anim.slide_to_right);
    }

    @Override
    public void onBackpressed() {
        super.onBackpressed();
        overridePendingTransitionExit();
        this.finish();
    }

    @Override
    public void onPause() {
        super.onPause();
    }

    @Override
    public void onResume() {
        super.onResume();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
    }

}

布局：

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true">

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <com.google.android.material.appbar.AppBarLayout
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@color/vista_green"
            app:elevation="0dp">
            <RelativeLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent">
                <androidx.appcompat.widget.Toolbar
                    android:id="@+id/toolbar"
                    app:navigationIcon="@drawable/ic_arrow_back_white"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:minHeight="?attr/actionBarSize"
                    app:elevation="0dp" />
                <TextView
                    android:text="Hello"
                    android:gravity="center"
                    android:textAppearance="@style/TitleBar"
                    android:layout_width="match_parent"
                    android:layout_height="?attr/actionBarSize" />
            </RelativeLayout>
        </com.google.android.material.appbar.AppBarLayout>

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <LinearLayout
                android:orientation="vertical"
                android:layout_width="match_parent"
                android:layout_height="match_parent">
                <androidx.appcompat.widget.AppCompatSpinner
                    android:id="@+id/spinner"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_margin="8dp"
                    android:padding="15dp"
                    android:gravity="center"
                    android:spinnerMode="dropdown" />
                <androidx.viewpager.widget.ViewPager
                    android:id="@+id/view_pager"
                    android:layout_marginTop="10dp"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    app:layout_behavior="@string/appbar_scrolling_view_behavior" />


            </LinearLayout>

            <View
                android:layout_alignParentBottom="true"
                android:layout_width="match_parent"
                android:layout_height="@dimen/spacing_medium"
                android:background="@drawable/brand_lines" />
        </RelativeLayout>

    </LinearLayout>

</androidx.coordinatorlayout.widget.CoordinatorLayout>