Java 如何为recycleview生成适配器类，以便在片段类中使用它？_Java_Android_Android Layout_Android Fragments_Android Room

Java 如何为recycleview生成适配器类，以便在片段类中使用它？

java android android-layout android-fragments

Java 如何为recycleview生成适配器类，以便在片段类中使用它？,java,android,android-layout,android-fragments,android-room,Java,Android,Android Layout,Android Fragments,Android Room,我正在尝试构建一个有片段的应用程序。在这些片段中，我使用了一个RecyclerView。此外，在我的layouts目录下还有一个用于Customer实体类的CardView小部件，名为card\u view\u Customer.xml。但是，当我在CustomerFragment.java类下为当前适配器创建一个实例时，由于我不知道的原因，应用程序正在崩溃。我相信问题在于我的适配器实现错误，但我不知道如何修复它。这些是目前的代码 onCreateView（）函数，位于CustomerFragm

我正在尝试构建一个有片段的应用程序。在这些片段中，我使用了一个RecyclerView。此外，在我的layouts目录下还有一个用于

Customer

实体类的CardView小部件，名为

card\u view\u Customer.xml

。但是，当我在

CustomerFragment.java

类下为当前适配器创建一个实例时，由于我不知道的原因，应用程序正在崩溃。我相信问题在于我的适配器实现错误，但我不知道如何修复它。这些是目前的代码

onCreateView（）
函数，位于
CustomerFragment.java

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_customer, container, false);
    // Inflate the layout for this fragment
    RecyclerView recyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
    final SalesTrackerAdapter adapter = new SalesTrackerAdapter(getActivity());
    recyclerView.setAdapter(adapter);
    recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
    mSalesTrackerViewModel = new ViewModelProvider(getActivity()).get(SalesTrackerViewModel.class);
    mSalesTrackerViewModel.getAllCustomers().observe(getActivity(), new Observer<List<Customer>>() {
        @Override
        public void onChanged(List<Customer> customers) {
            adapter.setCustomers(customers);
        }
    });
    return view;
}

<?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"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="10dp"
android:background="#00D8D8">

<androidx.cardview.widget.CardView
    android:id="@+id/card_view_customer"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:cardCornerRadius="4dp"
    app:contentPadding="10dp">

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

        <TextView
            android:id="@+id/customerTitle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            style="@style/customer_title"
            android:layout_alignParentStart="true" />

    </RelativeLayout>
</androidx.cardview.widget.CardView>

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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"
tools:context=".CustomerFragment">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0" />
</FrameLayout>

fragment\u customer.xml
我在哪里使用
RecyclerView

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_customer, container, false);
    // Inflate the layout for this fragment
    RecyclerView recyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
    final SalesTrackerAdapter adapter = new SalesTrackerAdapter(getActivity());
    recyclerView.setAdapter(adapter);
    recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
    mSalesTrackerViewModel = new ViewModelProvider(getActivity()).get(SalesTrackerViewModel.class);
    mSalesTrackerViewModel.getAllCustomers().observe(getActivity(), new Observer<List<Customer>>() {
        @Override
        public void onChanged(List<Customer> customers) {
            adapter.setCustomers(customers);
        }
    });
    return view;
}

<?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"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="10dp"
android:background="#00D8D8">

<androidx.cardview.widget.CardView
    android:id="@+id/card_view_customer"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:cardCornerRadius="4dp"
    app:contentPadding="10dp">

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

        <TextView
            android:id="@+id/customerTitle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            style="@style/customer_title"
            android:layout_alignParentStart="true" />

    </RelativeLayout>
</androidx.cardview.widget.CardView>

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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"
tools:context=".CustomerFragment">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0" />
</FrameLayout>

我相信这个适配器有问题，因为每当在

onCreateView（）中引用它时，emulator就会说应用程序“一直停止”。当我注释掉这些行时，到目前为止效果很好。我想要的是从数据库中获取客户，我已经实现了repository和viewmodel类，并将它们显示在片段下的CardView中。以下是my repository和ViewModel的代码：
public class SalesTrackerRepository {

    //Dao instances.
    private CustomerDao mCustomerDao;
    //Listing items.
    private LiveData<List<Customer>> mAllCustomers;


    SalesTrackerRepository(Application application){
        SalesTrackerDatabase db = SalesTrackerDatabase.getDatabase(application);
        mCustomerDao = db.customerDao();
        mAllCustomers = mCustomerDao.getCustomers();
    }

    LiveData<List<Customer>> getAllCustomers(){
        return mAllCustomers;
    }

    void insert(Customer customer){
        SalesTrackerDatabase.databaseWriteExecutor.execute(() -> mCustomerDao.insert(customer));
    }

}

公共类SalesTrackerRepository{
//Dao实例。
私人客户道；
//列出项目。
私人LiveData客户；
SalesTrackerRepository（应用程序）{
SalesTrackerDatabase db=SalesTrackerDatabase.getDatabase（应用程序）；
mcCustomerDao=db.customerDao（）；
mAllCustomers=mcCustomerDao.getCustomers（）；
}
LiveData getAllCustomers（）{
回报客户；
}
无效插入（客户）{
SalesTrackerDatabase.databaseWriteExecutor.execute（（）->MCCustomerDao.insert（customer））；
}
}

视图模型
public class SalesTrackerViewModel extends AndroidViewModel {

    private SalesTrackerRepository mRepository;

    private LiveData<List<Customer>> mAllCustomers;

    private SalesTrackerViewModel(Application application){
        super(application);
        mRepository = new SalesTrackerRepository(application);
        mAllCustomers = mRepository.getAllCustomers();
    }

    LiveData<List<Customer>> getAllCustomers(){return mAllCustomers;}

    public void insert(Customer customer){mRepository.insert(customer);}
}

公共类SalesTrackServiceModel扩展了AndroidViewModel{
私人SalesTrackerRepository；
私人LiveData客户；
专用SalesTrackServiceWModel（应用程序）{
超级（应用）；
mRepository=新SalesTrackerRepository（应用程序）；
mallcusters=mRepository.getAllCustomers（）；
}
LiveData getAllCustomers（）{return mAllCustomers；}
公共无效插入（客户）{mRepository.insert（客户）；}
}

我刚刚开始学习android，并试图学习这个项目。对不起，如果问题中有任何没有意义的地方。提前谢谢
编辑：问题也可能出现在ViewModel类中。我认为崩溃是由于以下阻塞造成的：
        mSalesTrackerViewModel = new ViewModelProvider(getActivity()).get(SalesTrackerViewModel.class);
    mSalesTrackerViewModel.getAllCustomers().observe(getActivity(), new Observer<List<Customer>>() {
        @Override
        public void onChanged(List<Customer> customers) {
            adapter.setCustomers(customers);
        }
    });

mSalesTrackerViewModel=newviewmodelprovider（getActivity（））.get（salestrackservicewmodel.class）；
msalStrackerViewModel.getAllCustomers（）.observe（getActivity（），new Observator（））{
@凌驾
更改后的公共作废（列出客户）{
adapter.setCustomers（客户）；
}
});

编辑2：这是我的日志
    2020-04-19 23:17:09.786 11114-11114/com.example.salestrackertest3 E/lestrackertest: Unknown bits set in runtime_flags: 0x8000
2020-04-19 23:17:12.011 11114-11114/com.example.salestrackertest3 E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.salestrackertest3, PID: 11114
    java.lang.RuntimeException: Cannot create an instance of class com.example.salestrackertest3.SalesTrackerViewModel
        at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:269)
        at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:106)
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:185)
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
        at com.example.salestrackertest3.CustomerFragment.onCreateView(CustomerFragment.java:90)
        at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2698)
        at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:310)
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1185)
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1354)
        at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1432)
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1495)
        at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:447)
        at androidx.fragment.app.FragmentManager.executeOps(FragmentManager.java:2167)
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1990)
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1945)
        at androidx.fragment.app.FragmentManager.execSingleAction(FragmentManager.java:1816)
        at androidx.fragment.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:303)
        at androidx.fragment.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:238)
        at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1244)
        at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1092)
        at androidx.viewpager.widget.ViewPager.onMeasure(ViewPager.java:1622)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at androidx.coordinatorlayout.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:760)
        at com.google.android.material.appbar.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:99)
        at com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1892)
        at androidx.coordinatorlayout.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:831)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at androidx.appcompat.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:143)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at com.android.internal.policy.DecorView.onMeasure(DecorView.java:742)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:3006)
2020-04-19 23:17:12.012 11114-11114/com.example.salestrackertest3 E/AndroidRuntime:     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1833)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2122)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1721)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7598)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:966)
        at android.view.Choreographer.doCallbacks(Choreographer.java:790)
        at android.view.Choreographer.doFrame(Choreographer.java:725)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:951)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
     Caused by: java.lang.NoSuchMethodException: com.example.salestrackertest3.SalesTrackerViewModel.<init> [class android.app.Application]
        at java.lang.Class.getConstructor0(Class.java:2332)
        at java.lang.Class.getConstructor(Class.java:1728)
        at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:267)
            ... 64 more

2020-04-19 23:17:09.786 11114-11114/com.example.salesstrackertest3 E/lestrackertest:运行时设置的未知位\u标志：0x8000
2020-04-19 23:17:12.0114-11114/com.example.salesstrackertest3e/AndroidRuntime:致命异常：main
进程：com.example.salestrackertest3，PID:11114
java.lang.RuntimeException:无法创建com.example.salestrackertest3.SalesTrackerServiceWModel类的实例
在androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create（ViewModelProvider.java:269）
在androidx.lifecycle.SavedStateViewModelFactory.create（SavedStateViewModelFactory.java:106）
位于androidx.lifecycle.ViewModelProvider.get（ViewModelProvider.java:185）
位于androidx.lifecycle.ViewModelProvider.get（ViewModelProvider.java:150）
在com.example.saleTrackerTest3.CustomerFragment.onCreateView（CustomerFragment.java:90）上
位于androidx.fragment.app.fragment.performCreateView（fragment.java:2698）
位于androidx.fragment.app.FragmentStateManager.createView（FragmentStateManager.java:310）
位于androidx.fragment.app.FragmentManager.moveToState（FragmentManager.java:1185）
位于androidx.fragment.app.FragmentManager.moveToState（FragmentManager.java:1354）
位于androidx.fragment.app.FragmentManager.moveFragmentToExpectedState（FragmentManager.java:1432）
位于androidx.fragment.app.FragmentManager.moveToState（FragmentManager.java:1495）
位于androidx.fragment.app.BackStackRecord.executeOps（BackStackRecord.java:447）
位于androidx.fragment.app.FragmentManager.executeOps（FragmentManager.java:2167）
在androidx.fragment.app.FragmentManager.ExecutePostGether（FragmentManager.java:1990）
位于androidx.fragment.app.FragmentManager.RemovedAndTopOperationsAndExecute（FragmentManager.java:1945）
位于androidx.fragment.app.FragmentManager.execSingleAction（FragmentManager.java:1816）
位于androidx.fragment.app.BackStackRecord.commitNowAllowingStateLoss（BackStackRecord.java:303）
位于androidx.fragment.app.FragmentPagerAdapter.finishUpdate（FragmentPagerAdapter.java:238）
在androidx.viewpager.widget.viewpager.populate中（viewpager.java:1244）
位于androidx.viewpager.widget.viewpager.populate（viewpager.java:1092）
在androidx.viewpager.widget.viewpager.onMeasure上（viewpager.java:1622）
在android.view.view.measure上（view.java:24530）
位于android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6828）
位于androidx.coordinatorlayout.widget.coordinatorlayout.onMeasureChild（coordinatorlayout.java:760）
位于com.google.android.material.appbar.HeaderScrollingViewBehavior.onMeasureChild（HeaderScrollingViewBehavior.java:99）
在com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior.onMeasureChild（AppBarLayout.java:1892）上
位于androidx.coordinatorlayout.widget.coordinatorlayout.onMeasure（coordinatorlayout.java:831）
在android.view.view