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Android：RecyclerViewAdapter中的GetApplication

[英]Android: GetApplication in RecyclerViewAdapter

 原文  2018-11-11 10:33:28  1   1    java/ android/ android-recyclerview/ android-context/ recyclerview-layout

問題描述

我想在Recyclerview的onClickListener方法內為Recyclerview充氣。

為此，我知道我必須從相應的活動中獲取上下文來設置LinearLayoutManager。

問題：由於我正在Fragment中使用Recyclerview來嘗試創建另一個Recyclerview，所以我不知道如何獲取正確的上下文。

我試過的

  • 在我的構造函數中使用FragmentActivity mContext，以后再嘗試通過“ mContext.getApplicationContext（）”獲取上下文 （從另一篇文章中獲取了FragmentActivity，預先使用了Context mContext）

准則中的問題：我將盡力分解准則：

  1. 從我嘗試初始化LinearLayoutManager的第一個Recyclerview中找到代碼

公共類deckbuilder_RViewAdapter_Card擴展了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);

        }
    }

  1. 我想初始化的Recyclerview中的代碼：

    公共類deckbuilder_RViewAdapter_List擴展了RecyclerView.Adapter { 

     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); } }

最后，請參閱我的Logcat： 

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)

要求的修改：

布局Cardview清單列表： 

<?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>

並且請在以下布局的末尾找到rv_deckbuilder_list： 

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:background="@drawable/background"
    >
    <LinearLayout
        android:id="@+id/llCarddeck"
        android:layout_width="0dp"
        android:layout_height="60dp"
        android:orientation="vertical"
        android:layout_marginEnd="10dp"
        android:weightSum="6"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="@id/gl_v_66"
        app:layout_constraintTop_toTopOf="parent"
        >

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="2"
            android:orientation="horizontal"
            android:weightSum="10">


            <LinearLayout
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="4.25">

                <TextView
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:gravity="center_horizontal"
                    android:paddingTop="1dp"
                    android:text="Rarity"
                    android:textColor="#fff"
                    android:textSize="15sp" />
            </LinearLayout>

            <LinearLayout
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="4.25">

                <TextView
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:gravity="center_horizontal"
                    android:paddingTop="1dp"
                    android:text="Category"
                    android:textColor="#fff"
                    android:textSize="15sp" />
            </LinearLayout>

            <TextView
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1.5"
                android:gravity="center_horizontal"
                android:paddingTop="1dp"
                android:text="Order"
                android:textColor="#fff"

                android:textSize="15sp" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="4"
            android:orientation="horizontal"
            android:weightSum="10">

            <LinearLayout
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_marginStart="1dp"
                android:layout_marginEnd="1dp"
                android:layout_weight="4.25"
                android:background="@drawable/x_linearlayoutcontainer_blank"
                android:weightSum="4">


                <ToggleButton
                    android:id="@+id/btnDeckbuilderBasic"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_marginStart="3dp"
                    android:layout_marginTop="3dp"
                    android:layout_marginBottom="3dp"

                    android:layout_weight="1"
                    android:background="@drawable/y_basic_layout" />

                <ToggleButton
                    android:id="@+id/btnDeckbuilderCommon"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_marginStart="3dp"
                    android:layout_marginTop="3dp"
                    android:layout_marginBottom="3dp"
                    android:layout_weight="1"
                    android:background="@drawable/y_common_layout" />

                <ToggleButton
                    android:id="@+id/btnDeckbuilderUncommon"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_marginStart="3dp"
                    android:layout_marginTop="3dp"
                    android:layout_marginBottom="3dp"
                    android:layout_weight="1"
                    android:background="@drawable/y_uncommon_layout" />

                <ToggleButton
                    android:id="@+id/btnDeckbuilderRare"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_marginStart="2.5dp"
                    android:layout_marginTop="2.5dp"
                    android:layout_marginEnd="3dp"
                    android:layout_marginBottom="2.5dp"
                    android:layout_weight="1"
                    android:background="@drawable/y_rare_layout" />

                <!--<TextView-->
                <!--android:id="@+id/textView"-->
                <!--android:layout_width="0dp"-->
                <!--android:layout_height="wrap_content"-->
                <!--android:layout_weight="1"-->
                <!--android:text="android:layout_weight=&quot;4.25&quot;&#xA;-->
                <!--android:layout_marginStart=&quot;1dp&quot;&#xA;                android:layout_marginEnd=&quot;1dp&quot;" />-->
            </LinearLayout>

            <LinearLayout
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_marginStart="1dp"
                android:layout_marginEnd="1dp"
                android:layout_weight="4.25"
                android:background="@drawable/x_linearlayoutcontainer_blank"
                android:weightSum="4"
                android:orientation="horizontal"
                >
                <android.support.v7.widget.AppCompatSpinner
                    android:id="@+id/spinnerDeckbuilderCategory"
                    android:layout_weight="2"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_marginStart="3dp"
                    android:autoSizeMaxTextSize="15sp"
                    android:autoSizeMinTextSize="10sp"
                    android:autoSizeTextType="uniform"
                    android:backgroundTint="@color/white"
                    android:dropDownWidth="match_parent"
                    android:popupBackground="#8A8A8A"
                    android:spinnerMode="dropdown"
                    android:textSize="15sp" />
                <android.support.v7.widget.AppCompatSpinner
                    android:id="@+id/spinnerDeckbuilder"
                    android:layout_weight="2"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"
                    android:layout_marginStart="1dp"

                    android:autoSizeMaxTextSize="15sp"
                    android:autoSizeMinTextSize="10sp"
                    android:autoSizeTextType="uniform"
                    android:backgroundTint="@color/white"
                    android:dropDownWidth="match_parent"

                    android:popupBackground="#8A8A8A"
                    android:spinnerMode="dropdown"
                    android:textSize="15sp" />

            </LinearLayout>

            <LinearLayout
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_marginStart="1dp"
                android:layout_marginEnd="1dp"
                android:layout_weight="1.5"
                android:background="@drawable/x_linearlayoutcontainer_blank">


                <FrameLayout
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center">

                    <android.support.v7.widget.SwitchCompat
                        android:id="@+id/switchDeckbuilders"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="center"
                        android:checked="false"
                        android:gravity="center|fill_horizontal"
                        android:showText="false" />
                </FrameLayout>


            </LinearLayout>

        </LinearLayout>
    </LinearLayout>

    <!--<android.support.v7.widget.RecyclerView-->
        <!--android:id="@+id/rv_deckbuilder_cards"-->
        <!--android:layout_width="0dp"-->
        <!--android:layout_height="0dp"-->
        <!--/>-->

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv_deckbuilder_cards"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginEnd="10dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="@id/gl_v_66"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/llCarddeck"
        />

    <LinearLayout
        android:id="@+id/llDecklist"
        android:layout_width="0dp"
        android:layout_height="30dp"
        android:background="@drawable/background"
        android:orientation="horizontal"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="@id/gl_v_66"
        app:layout_constraintEnd_toEndOf="parent"/>

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv_deckbuilder_list"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="@id/gl_v_66"
        app:layout_constraintTop_toBottomOf="@+id/llDecklist" />


    <!--</android.support.v7.widget.RecyclerView>-->



    <android.support.constraint.Guideline
        android:id="@+id/gl_v_66"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintGuide_percent="0.66"
        android:orientation="vertical" />



</android.support.constraint.ConstraintLayout>

要求的更新2.0：

第一個稱為rvCards的RV（通過deckbuilder_RViewAdapter_Cards）在以下片段中被誇大： 

public class deckbuilder_fragment extends Fragment {

//..
List<Cards> listCards;
    DBHelper dbHelper;
    RecyclerView rvCards;
//..

public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
//        return super.onCreateView(inflater, container, savedInstanceState);
        View view = inflater.inflate(R.layout.deckbuilder_fragment, container, false);
//.. 

//...
dbHelper = new DBHelper(getActivity().getApplicationContext());
        dbHelper.createDataBase();
        rvCards = view.findViewById(R.id.rv_deckbuilder_cards);
        updateAdapter();

return view;

}}

而適配器在以下位置更新： 

public void updateAdapter() {
        listCards = dbHelper.getDeckbuilderCards(spinnerDeckbuilderType.getSelectedItem().toString(), true, btnDeckbuilderBasic.isChecked(), btnDeckbuilderCommon.isChecked(), btnDeckbuilderUncommon.isChecked(),btnDeckbuilderRare.isChecked(), spinnerDeckbuilderCategory.getSelectedItem().toString());
        LinearLayoutManager layoutManagerCards = new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false);
        rvCards.setLayoutManager(layoutManagerCards);
        deckbuilder_RViewAdapter_Card newAdapterCards = new deckbuilder_RViewAdapter_Card(getActivity(), listCards);
        rvCards.setAdapter(newAdapterCards);

    }

1 個解決方案

解決方案1
 1 已采納  2018-11-11 12:05:13

我認為您只是從錯誤的位置獲取rvList ，不應將其放在視圖持有rvList ，而應將其放在片段中，這就是為什么單擊它時會引發NullPointerException。

首先，刪除rvList = introListView.findViewById(R.id.rv_deckbuilder_list); 從您的視圖持有者那里獲得，因為它只會返回null。

接下來，更新您的deckbuilder_RViewAdapter_List適配器，以便它可以支持數據更改： 

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();
}

並更新您的deckbuilder_RViewAdapter_Card適配器，以便它可以引用deckbuilder_RViewAdapter_List的引用： 

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);
        }
    });
}

最后，在您的片段中找到RecyclerView ，然后將它們附加到適當的適配器： 

@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);

    // ...
}

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