Question

尝试了解RecyclerView的工作原理，但无法完成代码。

它不显示任何错误，但是当我启动应用程序时，它会自动崩溃。

在logcat中我收到错误：

11-21 13：01：19.058 11109-11109 / com.crelix.crelix E / AndroidRuntime：致命异议：主要处理：com.crelix.crelix，PID：11109 java.lang.RuntimeException：无法启动活动 ComponentInfo {com.crelix.crelix / com.crelix.crelix.NavigationActivity}： java.lang.NullPointerException：尝试调用虚方法'void android.support.v7.widget.RecyclerView.setLayoutManager（android.support.v7.widget.RecyclerView $布局管理）” 在null对象引用上在 android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2455）在 android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2517）在android.app.ActivityThread.access $ 800（ActivityThread.java:162）在 android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1412）在android.os.Handler.dispatchMessage（Handler.java:106）在android.os.Looper.loop（Looper.java:189）在android.app.ActivityThread.main（ActivityThread.java:5529） at java.lang.reflect.Method.invoke（Native Method）在java.lang.reflect.Method.invoke（Method.java:372）在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:950）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:745）引起：java.lang.NullPointerException：尝试调用虚拟方法'无效 android.support.v7.widget.RecyclerView.setLayoutManager（android.support.v7.widget.RecyclerView $布局管理）” 在null对象引用上在 com.crelix.crelix.NavigationActivity.onCreate（NavigationActivity.java:78）在android.app.Activity.performCreate（Activity.java:5966）在 android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1106）在 android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2408）在 android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2517）在android.app.ActivityThread.access $ 800（ActivityThread.java:162）在 android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1412）在android.os.Handler.dispatchMessage（Handler.java:106）在android.os.Looper.loop（Looper.java:189）在android.app.ActivityThread.main（ActivityThread.java:5529） at java.lang.reflect.Method.invoke（Native Method）在java.lang.reflect.Method.invoke（Method.java:372）在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:950）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:745）

我的fragment_market.xml

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/MarketScroll"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:onClick="RefreshMarket">

<android.support.v7.widget.CardView
android:id="@+id/MarketView"
android:layout_width="100dp"
android:layout_height="120dp"
android:layout_margin="5dp">

<RelativeLayout
    android:background="#fff"
    android:elevation="4dp"
    android:padding="5dp"
    android:layout_width="match_parent"
    android:layout_height="120dp">

    <ImageView
        android:id="@+id/MarketImage"
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true" />

    <TextView
        android:id="@+id/MarketTitle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingBottom="5dp"
        android:text=""
        android:textSize="8sp"
        android:layout_below="@+id/MarketImage"
        android:layout_centerHorizontal="true" />

    <Button
        android:text="Sell"
        android:layout_width="50dp"
        android:layout_height="35dp"
        android:id="@+id/MarketButton"
        android:textSize="10sp"
        android:layout_below="@+id/MarketPrice"
        android:layout_centerHorizontal="true" />

    <TextView
        android:id="@+id/MarketCount"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Count: "
        android:textColor="#8b8b8b"
        android:textSize="9sp"
        android:layout_below="@+id/MarketTitle"
        android:layout_centerHorizontal="true" />

    <TextView
        android:id="@+id/MarketPrice"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Price: "
        android:textColor="#8b8b8b"
        android:textSize="9sp"
        android:layout_below="@+id/MarketCount"
        android:layout_centerHorizontal="true" />


</RelativeLayout>

我的MarketHolder.java

    package com.crelix.crelix;

    public class MarketHolder {
    private String title, count, price;
    private int imageId;

    public MarketHolder() {
    }

    public MarketHolder(int imageId, String title, String count, String price) {
        this.imageId = imageId;
        this.title = title;
        this.count = count;
        this.price = price;
    }

    public int getImage() {
        return imageId;
    }

    public void setImage(int imageId) {
        this.imageId = imageId;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getCount() {
        return count;
    }

    public void setCount(String count) {
        this.count = count;
    }

    public String getPrice() {
        return price;
    }

    public void setPrice(String price) {
        this.price = price;
    }
}

我的MarketAdapter.java

    package com.crelix.crelix;

    import android.support.v7.widget.RecyclerView;
    import android.view.LayoutInflater;

    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ImageView;
    import android.widget.TextView;

    import java.util.List;

    public class MarketAdapter extends 

    RecyclerView.Adapter<MarketAdapter.MyViewHolder> {
    private List<MarketHolder> MarketList;

    public class MyViewHolder extends RecyclerView.ViewHolder {
        public ImageView imageId;
        public TextView title, count, price;

        public MyViewHolder(View view) {
            super(view);
            imageId = (ImageView) view.findViewById(R.id.MarketImage) ;
            title = (TextView) view.findViewById(R.id.MarketTitle);
            count = (TextView) view.findViewById(R.id.MarketCount);
            price = (TextView) view.findViewById(R.id.MarketPrice);
        }
    }


    public MarketAdapter(List<MarketHolder> MarketList) {
        this.MarketList = MarketList;
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.fragment_market, parent, false);

        return new MyViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        MarketHolder Market = MarketList.get(position);
        holder.imageId.setImageResource(Market.getImage());
        holder.title.setText(Market.getTitle());
        holder.count.setText(Market.getCount());
        holder.price.setText(Market.getPrice());
    }

    @Override
    public int getItemCount() {
        return MarketList.size();
    }
}

主要活动，我在launc上收到错误

   private List<MarketHolder> MarketList = new ArrayList<>();
private RecyclerView recyclerView;
private MarketAdapter mAdapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    LoadFile();

    setContentView(R.layout.activity_navigation);

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.setDrawerListener(toggle);
    toggle.syncState();

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);


    recyclerView = (RecyclerView) findViewById(R.id.MarketView);

    mAdapter = new MarketAdapter(MarketList);
    RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
    recyclerView.setLayoutManager(mLayoutManager);
    recyclerView.setItemAnimator(new DefaultItemAnimator());


       recyclerView.setAdapter(mAdapter);
}
        prepareMarketData();

 private void prepareMarketData() {
    MarketHolder Market = new MarketHolder(R.drawable.box, "Test", "Count: " +Part.AccessoriesPartsLVL1[0],"Price: " +Part.AccessoriesPartsLVL1[3]);
    MarketList.add(Market);
    Market = new MarketHolder(R.drawable.box, "Test2", "Count: " +Part.AccessoriesPartsLVL1[4],"Price: " +Part.AccessoriesPartsLVL1[7]);
    MarketList.add(Market);
    Market = new MarketHolder(R.drawable.box, "Test3", "Count: " +Part.AccessoriesPartsLVL1[8],"Price: " +Part.AccessoriesPartsLVL1[10]);
    MarketList.add(Market);

    mAdapter.notifyDataSetChanged();
}


Activity_Navigation.xml


<?xml version="1.0" encoding="utf-8"?>

<include
    layout="@layout/app_bar_navigation"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

<android.support.design.widget.NavigationView
    android:id="@+id/nav_view"
    android:layout_width="200dp"
    android:layout_height="match_parent"
    android:layout_gravity="start"
    android:fitsSystemWindows="true"
    app:headerLayout="@layout/nav_header_navigation"
    app:menu="@menu/activity_navigation_drawer" />

Android studio RecyclerView在发布

0 个答案: