Question

绑定视图时收到此错误当我不添加任何标题时，代码工作正常视图正在初始化，数据将显示出来但每当我尝试添加标题时，我都会遇到此异常我已经初始化了所有的视图，但它不能仅仅获得参考并且突出显示的可能问题并没有解决问题，因为我在传递引用后绑定了Views 所以我在传递引用之前没有调用Views。

FATAL EXCEPTION: main
Process: com.example.shashankdc.learn, PID: 8615
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at com.example.shashankdc.learn.Medals.Medals_Adapter.onBindViewHolder(Medals_Adapter.java:62)
    at com.example.shashankdc.learn.Medals.Medals_Adapter.onBindViewHolder(Medals_Adapter.java:17)
    at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:5138)
    at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4433)
    at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4326)
    at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:1955)
    at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1364)
    at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1327)
    at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:556)
    at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:2713)
    at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:3011)
    at android.view.View.layout(View.java:15695)
    at android.view.ViewGroup.layout(ViewGroup.java:4981)
    at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1076)
    at android.view.View.layout(View.java:15695)
    at android.view.ViewGroup.layout(ViewGroup.java:4981)
    at android.support.design.widget.CoordinatorLayout.layoutChild(CoordinatorLayout.java:1009)
    at android.support.design.widget.CoordinatorLayout.onLayoutChild(CoordinatorLayout.java:719)
    at android.support.design.widget.ViewOffsetBehavior.onLayoutChild(ViewOffsetBehavior.java:42)
    at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onLayoutChild(AppBarLayout.java:984)
    at android.support.design.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:732)
    at android.view.View.layout(View.java:15695)
    at android.view.ViewGroup.layout(ViewGroup.java:4981)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
    at android.view.View.layout(View.java:15695)
    at android.view.ViewGroup.layout(ViewGroup.java:4981)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
    at android.view.View.layout(View.java:15695)
    at android.view.ViewGroup.layout(ViewGroup.java:4981)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
    at android.view.View.layout(View.java:15695)
    at android.view.ViewGroup.layout(ViewGroup.java:4981)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
    at android.view.View.layout(View.java:15695)
    at android.view.ViewGroup.layout(ViewGroup.java:4981)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
    at android.view.View.layout(View.java:15695)
    at android.view.ViewGroup.layout(ViewGroup.java:4981)
    at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2186)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1920)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1106)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6018)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:792)
    at android.view.Choreographer.doCallbacks(Choreographer.java:596)
    at android.view.Choreographer.doFrame(Choreographer.java:557)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:778)
    at android.os.Handler.handleCallback(Handler.java:739)

这是我的适配器

package com.example.shashankdc.learn.Medals;

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import com.example.shashankdc.learn.R;

import java.util.List;


public class Medals_Adapter extends RecyclerView.Adapter<Medals_Adapter.MyHolder> {

    private static final int TYPE_HEAD = 0;
    private static final int TYPE_LIST = 1;
    private List<Medals_Model> mylist;
    private Context context;

    public Medals_Adapter(List<Medals_Model> mylist, Context context) {
        this.mylist = mylist;
        this.context = context;
    }

    @Override
    public MyHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        if (viewType == TYPE_LIST) {

            View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.medals_card, parent, false);
            return new MyHolder(v, viewType);
        } else if (viewType == TYPE_HEAD) {
            View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.header_img, parent, false);
            return new MyHolder(v, viewType);
        }

        return null;
    }

    @Override
    public void onBindViewHolder(MyHolder holder, int position) {


        if (holder.view_type == TYPE_LIST) {

            Medals_Model model = mylist.get(position + 1);
            holder.name.setText(model.getName());
            holder.requirements.setText(model.getRequirements());
            holder.bronze.setText(String.valueOf(model.getBronze()));
            holder.silver.setText(String.valueOf(model.getSilver()));
            holder.gold.setText(String.valueOf(model.getGold()));

        } else if (holder.view_type == TYPE_HEAD) {

            holder.header.setText("HEADER");

        }


    }

    @Override
    public int getItemCount() {
        return mylist.size() + 1;
    }

    public void add(Medals_Model model) {
        mylist.add(model);
        notifyDataSetChanged();
    }

    @Override
    public int getItemViewType(int position) {
        if (position == 0) {
            return TYPE_HEAD;
        } else {
            return TYPE_LIST;
        }
    }

    public class MyHolder extends RecyclerView.ViewHolder {
        public TextView name, requirements, gold, silver, bronze;
        //Header
        public TextView header;
        int view_type;

        public MyHolder(View itemView, int view_type) {
            super(itemView);

            if (view_type == TYPE_LIST) {
                name = (TextView) itemView.findViewById(R.id.medals_title);
                requirements = (TextView) itemView.findViewById(R.id.medals_requirements);
                gold = (TextView) itemView.findViewById(R.id.medals_gold);
                silver = (TextView) itemView.findViewById(R.id.medals_silver);
                bronze = (TextView) itemView.findViewById(R.id.medals_bronze);
                view_type = 1;
            } else if (view_type == TYPE_HEAD) {
//Header_config
                header = (TextView) itemView.findViewById(R.id.my_header);
                view_type = 0;
            }


        }
    }

}

这是我的header_img.xml

  <LinearLayout 
  xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:card_view="http://schemas.android.com/apk/res-auto"
  android:orientation="horizontal" 
  android:layout_width="match_parent"
  android:layout_height="40dp">

  <android.support.v7.widget.CardView
    android:layout_width = "match_parent"
    android:layout_height = "wrap_content"
    card_view:cardCornerRadius="3dp">

   <TextView
       android:layout_width="match_parent"
       android:id="@+id/my_header"
       android:layout_height="wrap_content" />

</android.support.v7.widget.CardView>
</LinearLayout>

还有content_medals（Medal）.xml

  <?xml version="1.0" encoding="utf-8"?>
  <RelativeLayout 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"
  app:layout_behavior="@string/appbar_scrolling_view_behavior"
  tools:context="com.example.shashankdc.learn.Medals.Medals"
  tools:showIn="@layout/medals">
  <android.support.v7.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/recyclerView_medals"
    android:background="@drawable/linearlayour_gradient"
    />
  </RelativeLayout>

Answer 1

这些行正在更改参数，即shadowing字段。

view_type = 1;
view_type = 0;

请在ViewHolder构造函数中更新以限定您要设置的正确变量

public MyHolder(View itemView, int view_type) {
    super(itemView);

    this.view_type = view_type; // Do it here
    if (view_type == TYPE_LIST) {
        // Remove view_type = 1;
    } else if ( ... )
        // Remove view_type = 0;

您的错误是因为holder.view_type始终为0而导致类似于此情况的错误。

if (holder.view_type == TYPE_LIST) {

    Medals_Model model = mylist.get(position + 1);

    // Error because holder.name is not defined for a header
    holder.name.setText(model.getName());

或者，使用getItemViewType(position)而不是依赖holder.view_type

将标头添加到异构RecyclerView时出现NullPointerException

1 个答案: