Java Android:RecycleServiceAdapter中的GetApplication

我想在onClickListener方法中从一个Recyclerview中膨胀一个Recyclerview

为此，我知道我必须从相应的活动中获取上下文，以设置LinearLayoutManager

问题： 因为我正在使用一个Recyclerview in片段来尝试创建另一个Recyclerview，所以我不知道如何获得正确的上下文

我的尝试：

2018-11-11 17:46:15.589 21538-21538/com.example.chris.projectartifact E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.chris.projectartifact, PID: 21538
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
        at com.example.chris.projectartifact.b_deckbuilderTap.deckbuilder_RViewAdapter_Card$3.onClick(deckbuilder_RViewAdapter_Card.java:116)
        at android.view.View.performClick(View.java:6291)
        at android.view.View$PerformClick.run(View.java:24931)
        at android.os.Handler.handleCallback(Handler.java:808)
        at android.os.Handler.dispatchMessage(Handler.java:101)
        at android.os.Looper.loop(Looper.java:166)
        at android.app.ActivityThread.main(ActivityThread.java:7425)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)

• 在我的构造函数中使用FragmentActivity mContext，稍后尝试通过“mContext.getApplicationContext（）”获取上下文。（从另一篇文章中获取FragmentActivity，事先使用了context mContext）

代码中的问题： 我将尽可能地分解我的代码：

从我尝试初始化LinearLayoutManager的第一个Recyclerview中查找代码

公共类deckbuilder_RViewAdapter_卡扩展了RecyclerView.Adapter{

public deckbuilder_RViewAdapter_Card(FragmentActivity mContext, List<Cards> mData) {
                this.mData = mData;
                this.mContext = mContext;
            }

 public void onBindViewHolder(@NonNull final ViewHolder viewHolder, final int position) {
fab_deckbuilder_add.setOnClickListener(new View.OnClickListener() {
            @Override
public void onClick(View view) {

List<Decklist> listCards = new ArrayList<>();
                listCards.add(new Decklist( ... );

LinearLayoutManager layoutManagerCards = new LinearLayoutManager(mContext.getApplicationContext(), LinearLayoutManager.VERTICAL, false);
                rvList.setLayoutManager(layoutManagerCards);
                deckbuilder_RViewAdapter_List addCardAdapter = new deckbuilder_RViewAdapter_List(mContext, listCards);
                rvList.setAdapter(addCardAdapter);
}
        });


    }

public int getItemCount() {
        return mData.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder{
        ImageView ivCardImage;
        TextView tvCardName;

        public ViewHolder(@NonNull View introListView) {
            super(introListView);
            fab_deckbuilder_add = introListView.findViewById(R.id.fab_deckbuilder_add);
            fab_deckbuilder_remove = introListView.findViewById(R.id.fab_deckbuilder_remove);
            rvList = introListView.findViewById(R.id.rv_deckbuilder_list);

        }
    }

private List<Decklist> mDecklist;
private Context mContext;

public deckbuilder_RViewAdapter_List (Context mContext, List<Decklist> mDecklist) {
    this.mDecklist = mDecklist;
    this.mContext = mContext;
}

@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {

    View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.layout_cardview_deckbuilder_list, viewGroup, false);
    return new deckbuilder_RViewAdapter_List.ViewHolder(view);
}

@Override
public void onBindViewHolder(@NonNull ViewHolder viewHolder, int position) {
    viewHolder.ivCard.setImageResource(mDecklist.get(position).getCardImage());
    viewHolder.ivType.setImageResource(mDecklist.get(position).getTypeImage());
    viewHolder.tvName.setText(mDecklist.get(position).getName());
    viewHolder.tvCost.setText(mDecklist.get(position).getCost());
    viewHolder.tvNumber.setText(mDecklist.get(position).getNumber());
}


public int getItemCount() {
    return mDecklist.size();
}

public class ViewHolder extends RecyclerView.ViewHolder{
    ImageView ivCard, ivType;
    TextView tvName, tvCost, tvNumber;

    public ViewHolder(@NonNull View itemView) {
        super(itemView);
        ivCard = itemView.findViewById(R.id.ivDecklistCardImage);
        ivType = itemView.findViewById(R.id.ivDecklistTypeImage);
        tvName = itemView.findViewById(R.id.tvDecklistName);
        tvCost = itemView.findViewById(R.id.tvDecklistCost);
        tvNumber = itemView.findViewById(R.id.tvDecklistNumber);
    }
}

请求的编辑：

2018-11-11 17:46:15.589 21538-21538/com.example.chris.projectartifact E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.chris.projectartifact, PID: 21538
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
        at com.example.chris.projectartifact.b_deckbuilderTap.deckbuilder_RViewAdapter_Card$3.onClick(deckbuilder_RViewAdapter_Card.java:116)
        at android.view.View.performClick(View.java:6291)
        at android.view.View$PerformClick.run(View.java:24931)
        at android.os.Handler.handleCallback(Handler.java:808)
        at android.os.Handler.dispatchMessage(Handler.java:101)
        at android.os.Looper.loop(Looper.java:166)
        at android.app.ActivityThread.main(ActivityThread.java:7425)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)

布局卡片视图甲板列表：

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/cardView_deckbuilder_list_id"
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:cardview= "http://schemas.android.com/apk/res-auto"
    android:layout_width="150dp"
    android:layout_height="20dp"
    android:layout_marginTop="5dp"
    cardview:cardCornerRadius="5dp"
    android:layout_marginStart="5dp"
    android:clickable="true"
    android:foreground="?android:attr/selectableItemBackground"
    >

    <android.support.constraint.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@drawable/background"
        android:orientation="vertical">

        <de.hdodenhof.circleimageview.CircleImageView
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:src="@drawable/axe"
            cardview:layout_constraintEnd_toStartOf="@id/gl_v_db_list"
            cardview:layout_constraintStart_toStartOf="parent" />

        <ImageView
            android:id="@+id/ivDecklistCardImage"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:adjustViewBounds="true"
            android:scaleType="centerCrop"
            android:scrollY="-7dp"
            android:src="@drawable/thunder_gods_wrath"
            cardview:layout_constraintEnd_toStartOf="@id/gl_v_db_list"
            cardview:layout_constraintStart_toStartOf="parent" />
        <de.hdodenhof.circleimageview.CircleImageView
            android:id="@+id/ivDecklistTypeImage"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:src="@drawable/introspells"
            cardview:layout_constraintEnd_toStartOf="@id/gl_v_db_list_secound"
            cardview:layout_constraintStart_toStartOf="@id/gl_v_db_list" />



        <TextView
            android:id="@+id/tvDecklistCost"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            cardview:layout_constraintStart_toStartOf="@id/gl_v_db_list_secound"
            android:text="20"
            android:autoSizeMaxTextSize="16sp"
            android:autoSizeMinTextSize="8sp"
            android:autoSizeTextType="uniform"
            android:gravity="center"
            android:textColor="#ffffff"
            cardview:layout_constraintEnd_toEndOf="@id/gl_v_db_list_third"/>
        <TextView
            android:id="@+id/tvDecklistName"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            cardview:layout_constraintStart_toStartOf="@id/gl_v_db_list_third"
            android:text="Thunder"
            android:autoSizeMaxTextSize="20sp"
            android:autoSizeMinTextSize="8sp"
            android:autoSizeTextType="uniform"
            android:gravity="center"
            android:textColor="#ffffff"
            cardview:layout_constraintEnd_toEndOf="@id/gl_v_db_list_last"/>

        <TextView
            android:id="@+id/tvDecklistNumber"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:text="x3"
            android:autoSizeMaxTextSize="16sp"
            android:autoSizeMinTextSize="8sp"
            android:autoSizeTextType="uniform"
            android:gravity="center"
            android:textColor="#ffff"
            cardview:layout_constraintEnd_toEndOf="parent"
            cardview:layout_constraintStart_toStartOf="@id/gl_v_db_list_last" />

        <android.support.constraint.Guideline
            android:id="@+id/gl_v_db_list"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            cardview:layout_constraintGuide_begin="20dp" />
        <android.support.constraint.Guideline
            android:id="@+id/gl_v_db_list_secound"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            cardview:layout_constraintGuide_begin="40dp" />
        <android.support.constraint.Guideline
            android:id="@+id/gl_v_db_list_third"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            cardview:layout_constraintGuide_begin="55dp" />

        <android.support.constraint.Guideline
            android:id="@+id/gl_v_db_list_last"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            cardview:layout_constraintGuide_end="15dp" />


    </android.support.constraint.ConstraintLayout>
</android.support.v7.widget.CardView>

---

我认为你只是从错误的地方得到了

rvList

，它不应该在你的视图持有者中，它应该在你的片段中，这就是为什么当你点击它时它会抛出NullPointerException

首先，从视图保持器中删除

rvList=introListView.findViewById（R.id.rv_deckbuilder_list）；

，因为它只返回null

接下来，更新您的

deckbuilder\u RViewAdapter\u列表

适配器，使其能够支持数据更改：

public deckbuilder_RViewAdapter_List (Context mContext, List<Decklist> mDecklist) {
    this.mDecklist = mDecklist;
    this.mContext = mContext;
}

public void setCards(List<Decklist> mDecklist) {
    this.mDecklist = mDecklist;
    notifyDataSetChanged();
}

最后，在片段中找到

RecyclerView

s，然后用适当的适配器连接它们：

@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

    // ... after inflate view

    rvCards = view.findViewById(R.id.rv_deckbuilder_cards)
    rvList = view.findViewById(R.id.rv_deckbuilder_list)

    deckbuilder_RViewAdapter_List listAdapter = new deckbuilder_RViewAdapter_List(..)
    deckbuilder_RViewAdapter_Card cardAdapter = new deckbuilder_RViewAdapter_Card(.., listAdapter)
    rvCards.setAdapter(cardAdapter);
    rvList.setAdapter(listAdapter);

    // ...
}

---

问题似乎出在“rvList”上。它是什么？在哪里给它赋值？@theblitz在我的公共类Viewholder中它正在初始化。@theblitz它正在初始化为RecyclerView rvList；以及。嘿@Aaron我实现了你的建议，但我仍然有相同的错误。我想将LinearLayoutManager设置为一个新的RecyclerView。我想使用find的地方ViewById位于第一个Recyclerview的Viewholder中，因为我正在使用第一个Recyclerview中的一个按钮调用新的Recyclerview…但我仍然有相同的错误..还有其他建议吗？我能帮你做点什么吗？总之，我对上下文的概念还不熟悉。因为我认为我的视图在片段中，所以我需要获取上下文我错了吗？谢谢你到目前为止的帮助。好的，你能和我分享一下布局图，以及包括rv的布局图吗？我做到了。希望这对@Aaron有帮助。：）我想我知道你在做什么。首先，你肯定不需要这些行

rvList=introListView、 findViewById（R.id.rv_deckbuilder_list）；

因为我认为它不在项目视图中。接下来，您可能想将

rvList

传递给适配器。@Christian.gruener我已经更新了我的答案，希望它对您有用。

public deckbuilder_RViewAdapter_List (Context mContext, List<Decklist> mDecklist) {
    this.mDecklist = mDecklist;
    this.mContext = mContext;
}

public void setCards(List<Decklist> mDecklist) {
    this.mDecklist = mDecklist;
    notifyDataSetChanged();
}

private deckbuilder_RViewAdapter_List mCardListAdapter;

public deckbuilder_RViewAdapter_Card(FragmentActivity mContext, List<Cards> mData, deckbuilder_RViewAdapter_List mCardListAdapter) {
    this.mData = mData;
    this.mContext = mContext;
    this.mCardListAdapter = mCardListAdapter;
}

public void onBindViewHolder(@NonNull final ViewHolder viewHolder, final int position) {
    fab_deckbuilder_add.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            List<Decklist> listCards = new ArrayList<>();
            listCards.add(new Decklist( ... );

            mCardListAdapter.setCards(listCards);
        }
    });
}

@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

    // ... after inflate view

    rvCards = view.findViewById(R.id.rv_deckbuilder_cards)
    rvList = view.findViewById(R.id.rv_deckbuilder_list)

    deckbuilder_RViewAdapter_List listAdapter = new deckbuilder_RViewAdapter_List(..)
    deckbuilder_RViewAdapter_Card cardAdapter = new deckbuilder_RViewAdapter_Card(.., listAdapter)
    rvCards.setAdapter(cardAdapter);
    rvList.setAdapter(listAdapter);

    // ...
}