android - 使用 Retrofit 从服务器获取多个 View 项目来创建 RecyclerView

Question

场景:

我正在尝试创建一个 RecyclerView，它将在一个列表中显示几种不同的项目(食物、书籍、食谱)。当用户在搜索栏中输入一些关键字时，数据将在改造的帮助下从服务器获取。因此，我有一个带有搜索栏的 Activity，另一个用于在回收站 View 中显示数据。

到目前为止做了什么:1. 借助回收站搜索 View 从服务器获取数据。2. 将数据(以可序列化的形式)从搜索 Activity 发送到显示 Activity 。3. 使用多 View 适配器创建回收器 View (在下面列出的一些教程的帮助下)。

链接:

1. Example 1

2. Example 2

一些相关项目:

1. Some Example Project

理解

到目前为止我所了解的是，为了在回收站 View 中显示多种类型的项目，我们需要创建一个抽象 View 持有者以及每个对象的单独 View 持有者。它们还必须具有相应的布局，并且它们的布局会动态地膨胀到回收器 View 容器中。

问题:

1. 尝试将适配器设置为我的回收站 View 适配器时出错。
2. 我面临的问题是我似乎无法将从服务器接收到的数据与相应的 View 持有者绑定(bind)。

代码:

我将省略我正在获取数据的 Activity ，因为它正在工作。

SearhResultActivity(此 Activity 从 SearchActivity 接收数据并应该显示带有数据的回收站 View )

package com.example.naisse.Activity;

import android.os.Bundle;
import android.support.v4.app.FragmentManager;
import android.support.v7.widget.RecyclerView;
import android.widget.FrameLayout;
import com.example.naisse.AdapterAndClass.ResultAdaptar;
import com.example.naisse.AdapterAndClass.SearchRecyclerAdapter;
import com.example.naisse.Api.Model.Search.Article;
import com.example.naisse.Api.Model.Search.Food;
import com.example.naisse.Api.Model.Search.Hadith;
import com.example.naisse.Api.Model.Search.Manuscript;
import com.example.naisse.Api.Model.Search.Quran;
import com.example.naisse.Fragment.SearchTabFragment;
import com.example.naisse.R;
import java.util.ArrayList;
import java.util.List;
import butterknife.BindView;

public class SearchResultActivity extends HomeActivity {

private static final String TAG = "SearchResultActivity";

@BindView(R.id.search_result_recycler)
RecyclerView recyclerView;

private SearchRecyclerAdapter searchRecyclerAdapter;

private List<String> dataList;

protected FrameLayout frames;
private FragmentManager mFragmentManager;
private ResultAdaptar resultAdaptar;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_search_result);

    frames = findViewById(R.id.search_bar_holder);
    mFragmentManager = (this).getSupportFragmentManager();
    mFragmentManager.beginTransaction().add(R.id.search_bar_holder, new SearchTabFragment()).commit();


    Food foodData = new Food();
    ArrayList<Book> getBookArray = new ArrayList<>();
    ArrayList<Recipe> getRecipe = new ArrayList<>();

    foodData = (Food) getIntent().getSerializableExtra("foodDetails");
    getBookArray = (ArrayList<Book>) getIntent().getSerializableExtra("bookList");
    getRecipe = (ArrayList<Recipe>) getIntent().getSerializableExtra("recipeList");

    /*There is something wrong here, it says "Attempt to invoke virtual method on a null object reference" for searchRecyclerAdapter*/
    searchRecyclerAdapter = new SearchRecyclerAdapter(this);
    recyclerView.setAdapter(searchRecyclerAdapter);

}

}

SearchRecyclerAdapter(此适配器包含用于声明和将所有 viewHolder 连接到抽象 viewHolder 并连接到回收器 View 的代码)

package com.example.naisse.AdapterAndClass;

import android.content.Context;
import android.support.annotation.NonNull;
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.naisse.Api.Model.Search.Food;
import com.example.naisse.Api.Model.Search.Quran;
import com.example.naisse.R;
import java.util.ArrayList;
import java.util.List;
import butterknife.BindView;
import butterknife.ButterKnife;

public class SearchRecyclerAdapter extends RecyclerView.Adapter<SearchRecyclerAdapter.AbstractViewHolder>{

private static final String TAG = "SearchRecyclerAdapter";

public static final int TYPE_FOOD = 0;
public static final int TYPE_BOOK = 1;


private Context context;
private List<Object> data;

/*I belive im missing something here*/
public SearchRecyclerAdapter(Context context){
    this.context = context;
}

public void add(List searchData){
    if(data == null){
        data = new ArrayList<>();
    }
    data.clear();
    data.addAll(searchData);
    notifyDataSetChanged();
}


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

    switch (i){
        case TYPE_FOOD:{
            /*search_result_fragment is the xml layout for food adapter*/
            View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.search_result_fragment, viewGroup, false);
            return new FoodViewAdapter(view);
        }
        case TYPE_BOOK:{
            /*search_result_fragment is the xml layout for book adapter*/
            View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.viewholder_book, viewGroup, false);
            return new BooksViewAdapter(view);
        }

        default:
            throw new IllegalArgumentException("Invalid view type");

    }

}

@Override
public void onBindViewHolder(AbstractViewHolder abstractViewHolder, int i) {
    Object object = data.get(i);
    abstractViewHolder.bind(object);
}

@Override
public int getItemViewType(int i){
    Object object = data.get(i);

    if (object instanceof Food){
        return TYPE_FOOD;
    }else if (object instanceof Book){
        return TYPE_BOOK;
    }

    throw new IllegalArgumentException("Invalid position");
}

@Override
public int getItemCount() {
    return data == null ? 0 : data.size();
}

public abstract class AbstractViewHolder<T> extends RecyclerView.ViewHolder{

    public AbstractViewHolder(@NonNull View itemView) {
        super(itemView);

        ButterKnife.bind(this, itemView);
    }

    public abstract void bind(T type);
}


public class FoodViewAdapter extends AbstractViewHolder<Food> {
    @BindView(R.id.result_food_title)
    TextView foodTitle;
    @BindView(R.id.result_food_content)
    TextView content;

    private FoodViewAdapter(View itemView){
        super(itemView);
    }

    @Override
    public void bind(Food type) {
        foodTitle.setText("Food");
        content.setText("title");
    }

}

public class BooksViewAdapter extends AbstractViewHolder<Book> {
    @BindView(R.id.result_book_title)
    TextView bookTitle;
    @BindView(R.id.result_book_content)
    TextView content;

    private BooksViewAdapter(View itemView){
        super(itemView);
    }

    @Override
    public void bind(Book type) {
        bookTitle.setText("title");
        content.setText("Text");
    }

}

}

问题:

How do i set the adapter and how do I bind my data to the corresponding views?

P.S 如果您想查看其他类或 XML 布局，请告诉我。

日志

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.naisse, PID: 12570
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.naisse/com.example.naisse.Activity.SearchResultActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setAdapter(android.support.v7.widget.RecyclerView$Adapter)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setAdapter(android.support.v7.widget.RecyclerView$Adapter)' on a null object reference
    at com.example.naisse.Activity.SearchResultActivity.onCreate(SearchResultActivity.java:67)
    at android.app.Activity.performCreate(Activity.java:7136)
    at android.app.Activity.performCreate(Activity.java:7127)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
    at android.os.Handler.dispatchMessage(Handler.java:106) 
    at android.os.Looper.loop(Looper.java:193) 
    at android.app.ActivityThread.main(ActivityThread.java:6669) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 

Answer 1

您使用 butterknife并忘记在 Activity 中添加绑定(bind) View

只需添加这一行

ButterKnife.bind(this);

到您的 SearchResultActivity 的 onCreate()

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_search_result);
    ButterKnife.bind(this);
    //other codes
}

第二部分

对于第二部分，您需要将数据添加到您的recycelerView(适配器)

为此，我们更改了适配器中的添加功能。使用此代码代替您的代码

public void add(ArrayList newData){
    if(data == null){
        data = new ArrayList<>();
    }
    data.addAll(searchData);
    notifyDataSetChanged();
}

现在在 SearchResultActivity 中尝试像这样将数据发送到适配器

searchRecyclerAdapter = new SearchRecyclerAdapter(this);
recyclerView.setAdapter(searchRecyclerAdapter);
searchRecyclerAdapter.add(foodData);
searchRecyclerAdapter.add(getBookArray);
searchRecyclerAdapter.add(getRecipe);