RecyclerView不加载数据，什么都不显示

Question

我是一名Android初学者，正在努力实现RecyclerView。正在通过一个教程并将值改为我所需要的。但是当我开始时，视图保持空白。就我的计划而言，目前它应该显示20倍的相同项目。

ExerciseList.java（开始活动）：

package com.example.erik.orlandoapp; 

import android.os.Bundle; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 

public class ExerciseList extends AppCompatActivity { 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setTitle(getString(R.string.title_activity_exercise_list)); 
     setContentView(R.layout.activity_exercise_list); 
     Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
     setSupportActionBar(toolbar); 
    } 
} 

ExerciseBlock.java：

package com.example.erik.orlandoapp; 

import java.util.ArrayList; 
import java.util.List; 

public class ExerciseBlock { 

    private String title; 
    private int difficulty; 
    private int exerciseId; 

    private static int lastId = 0; 

    public ExerciseBlock(String title, int difficulty, int exerciseId) { 
     this.title = title; 
     this.difficulty = difficulty; 
     this.exerciseId = exerciseId; 
    } 

    public String getTitle() { 
     return title; 
    } 

    public int getDifficulty() { 
     return difficulty; 
    } 

    public int getExerciseId() { 
     return exerciseId; 
    } 

    public static ArrayList<ExerciseBlock> createContactsList(int numContacts) { 
     ArrayList<ExerciseBlock> exerciseBlocks = new ArrayList<ExerciseBlock>(); 

     for (int i = 1; i <= numContacts; i++) { 
      exerciseBlocks.add(new ExerciseBlock("Title",1,1)); 
     } 

     return exerciseBlocks; 
    } 

} 

ExerciseBlockAdapter.java：

package com.example.erik.orlandoapp; 
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 java.util.List; 


public class ExerciseBlockAdapter extends RecyclerView.Adapter<ExerciseBlockAdapter.ViewHolder> { 

    private List<ExerciseBlock> exList; 
    private Context mContext; 

    @Override 
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { 
     Context context = parent.getContext(); 
     LayoutInflater inflater = LayoutInflater.from(context); 
     View contactView = inflater.inflate(R.layout.exercise_item, parent, false); 
     ViewHolder viewHolder = new ViewHolder(contactView); 
     return viewHolder; 
    } 

    @Override 
    public void onBindViewHolder(ViewHolder viewHolder, int position) { 
     ExerciseBlock exBlock = exList.get(position); 
     TextView textView = viewHolder.getTxtDiff(); 
     textView.setText(exBlock.getDifficulty()); 

     textView = viewHolder.getTxtExercise(); 
     textView.setText(exBlock.getExerciseId()); 
    } 

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

    public ExerciseBlockAdapter(Context context, List<ExerciseBlock> exList) { 
     this.exList = exList; 
     this.mContext = context; 
    } 

    public static class ViewHolder extends RecyclerView.ViewHolder { 

     private TextView txtExercise; 
     private TextView txtDiff; 

     public TextView getTxtExercise() { 
      return this.txtExercise; 
     } 

     public TextView getTxtDiff() { 
      return this.txtDiff; 
     } 

     public ViewHolder(View itemView) { 
      super(itemView); 

      txtDiff = (TextView) itemView.findViewById(R.id.txtExDiff); 
      txtExercise = (TextView) itemView.findViewById(R.id.txtExName); 
     } 
    } 
} 

UserListActivity：

package com.example.erik.orlandoapp; 

import android.os.Bundle; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.LinearLayoutManager; 
import android.support.v7.widget.RecyclerView; 

import java.util.ArrayList; 

public class UserListActivity extends AppCompatActivity { 

    ArrayList<ExerciseBlock> exerciseBlocks; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     RecyclerView rvContacts = (RecyclerView) findViewById(R.id.exerciseList); 

     exerciseBlocks = ExerciseBlock.createContactsList(20); 
     ExerciseBlockAdapter adapter = new ExerciseBlockAdapter(this, exerciseBlocks); 
     rvContacts.setAdapter(adapter); 
     rvContacts.setLayoutManager(new LinearLayoutManager(this)); 
    } 
} 

activity_exercise_list.xml：

<?xml version="1.0" encoding="utf-8"?> 
<android.support.design.widget.CoordinatorLayout 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" 
    android:fitsSystemWindows="true" 
    tools:context="com.example.erik.orlandoapp.ExerciseList"> 


    <LinearLayout 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:orientation="vertical"> 

     <android.support.design.widget.AppBarLayout 
      android:id="@+id/appbar" 
      android:layout_width="match_parent" 
      android:layout_height="wrap_content" 
      android:paddingTop="@dimen/appbar_padding_top" 
      android:theme="@style/AppTheme.AppBarOverlay"> 

      <android.support.v7.widget.Toolbar 
       android:id="@+id/toolbar" 
       android:layout_width="match_parent" 
       android:layout_height="?attr/actionBarSize" 
       android:background="?attr/colorPrimary" 
       app:layout_scrollFlags="scroll|enterAlways" 
       app:popupTheme="@style/AppTheme.PopupOverlay"> 

      </android.support.v7.widget.Toolbar> 

     </android.support.design.widget.AppBarLayout> 

     <android.support.v7.widget.RecyclerView 
      android:id="@+id/exerciseList" 
      android:layout_width="match_parent" 
      android:layout_height="fill_parent" 
      android:layout_marginBottom="20dp" 
      app:layout_behavior="@string/appbar_scrolling_view_behavior" /> 

    </LinearLayout> 

</android.support.design.widget.CoordinatorLayout> 

exercise_item.xml：

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    android:orientation="horizontal" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:paddingTop="10dp" 
    android:paddingBottom="10dp" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:weightSum="1"> 


    <TextView 
     android:id="@+id/txtExName" 
     android:layout_width="0dp" 
     android:layout_height="wrap_content" 
     android:layout_weight="1" 
     android:text="Whatever" /> 

    <TextView 
     android:id="@+id/txtExDiff" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:background="@color/colorDifEasy" 
     android:paddingBottom="6dp" 
     android:paddingLeft="16dp" 
     android:paddingRight="16dp" 
     android:paddingTop="6dp" 
     android:text="Leicht" 
     android:textSize="10sp" /> 


</LinearLayout> 

非常感谢！

Answer 1

我没有看到UserListActivity调用的setContentView（） 要么把这个代码ExersiceList活动中

RecyclerView rvContacts = (RecyclerView) findViewById(R.id.exerciseList); 

     exerciseBlocks = ExerciseBlock.createContactsList(20); 
     ExerciseBlockAdapter adapter = new ExerciseBlockAdapter(this, exerciseBlocks); 
     rvContacts.setAdapter(adapter); 
     rvContacts.setLayoutManager(new LinearLayoutManager(this)); 

或您UserListActivity调用的setContentView（R.layout.activity_exercise_layout）