将cardView放入标签片段

Question

如果您愿意，这里是项目的链接，这里的帖子有点大。 https://drive.google.com/open?id=1cmbrJMUK56wCKdePiunXHoTRxwBj4tWy

我遵循了两个教程。一个是如何创建一个带有卡片的回收器，另一个是创建一个标签布局。我想将两者结合起来，以便卡片位于选项卡片段中。

这是我的主要活动：

package com.example.growdiary;

import android.net.Uri;
import android.os.Bundle;

import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.android.material.snackbar.Snackbar;

import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;

import android.view.View;
import android.view.Menu;
import android.view.MenuItem;

import com.google.android.material.tabs.TabLayout;

import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import androidx.viewpager.widget.ViewPager;
import androidx.viewpager.widget.PagerAdapter;



public class MainActivity extends AppCompatActivity implements
        Tab1Fragment.OnFragmentInteractionListener,
        Tab2Fragment.OnFragmentInteractionListener,
        Tab3Fragment.OnFragmentInteractionListener,
        Tab4Fragment.OnFragmentInteractionListener {

    RecyclerView recyclerView;
    RecyclerView.LayoutManager layoutManager;
    RecyclerView.Adapter adapter;

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


        recyclerView = findViewById(R.id.recycler_view);

        layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);

        adapter = new com.example.growdiary.RecyclerAdapter();
        recyclerView.setAdapter(adapter);



        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
        configureTabLayout();
    }


    private void configureTabLayout() {
            TabLayout tabLayout = findViewById(R.id.tab_layout);

        tabLayout.addTab(tabLayout.newTab().setText("Tab 1 Item"));
        tabLayout.addTab(tabLayout.newTab().setText("Tab 2 Item"));
        tabLayout.addTab(tabLayout.newTab().setText("Tab 3 Item"));
        tabLayout.addTab(tabLayout.newTab().setText("Tab 4 Item"));

        final ViewPager viewPager = findViewById(R.id.pager);
        final PagerAdapter adapter = new TabPagerAdapter(getSupportFragmentManager(), tabLayout.getTabCount());
        viewPager.setAdapter(adapter);

        viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
        tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                viewPager.setCurrentItem(tab.getPosition());
            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab) {

            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {

            }
        });
    }

    @Override
    public void onFragmentInteraction(Uri uri) {

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

}

这是 1 个标签片段

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:id="@+id/frameLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".Tab1Fragment">

    <TextView
        android:id="@+id/textView3"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="Tab 1 Fragment" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />


</androidx.constraintlayout.widget.ConstraintLayout>

我在运行时得到这个错误输出

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.growdiary, PID: 24355
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.growdiary/com.example.growdiary.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setLayoutManager(androidx.recyclerview.widget.RecyclerView$LayoutManager)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3047)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3182)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1916)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6898)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:537)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setLayoutManager(androidx.recyclerview.widget.RecyclerView$LayoutManager)' on a null object reference
        at com.example.growdiary.MainActivity.onCreate(MainActivity.java:46)
        at android.app.Activity.performCreate(Activity.java:7149)
        at android.app.Activity.performCreate(Activity.java:7140)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1288)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3027)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3182) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1916) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:193) 
        at android.app.ActivityThread.main(ActivityThread.java:6898) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:537) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 

如果我将回收器 xml 放在 content_main.xml 中，它可以工作，但我的选项卡不再工作。我正在学习如何在 Java 中完成所有这些事情，但是将它们全部组合在一起有点困难，谢谢。

Answer 1

好吧，伙计们，我自己想通了。我把它移出了主要的 java 类

recyclerView = findViewById(R.id.recycler_view);

layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);

adapter = new com.example.growdiary.RecyclerAdapter();
recyclerView.setAdapter(adapter);

进入对应的tab1 java类

然后我遇到了一些错误并进行了一些更改。

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_tab1, container, false);

        recyclerView = (RecyclerView) view.findViewById(R.id.recycler_view); <-- added view to findViewById(R.id.recycler_view);

        layoutManager = new LinearLayoutManager(this.getActivity()); <--added getActivity
        recyclerView.setLayoutManager(layoutManager);

        adapter = new com.example.growdiary.RecyclerAdapter();
        recyclerView.setAdapter(adapter);

        // Inflate the layout for this fragment
        return view;
    }