Android Studio 之 ROM【3】，LiveData+ViewModel+AsyncTask+Repository+RecyclerView

教程地址：https://www.bilibili.com/video/av65180549

源码地址：https://github.com/longway777/Android-2019-Tutorial-RoomBasic-step-3

RecyclerView 是一个回收视图，当滚动出屏幕外面的内容会自动回收，回收系统资源

相同的内容，支持用不同的样式来呈现！

创建2个 Layout 资源文件

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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="wrap_content"
    android:background="?attr/selectableItemBackground"
    android:clickable="true">

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.1" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.85" />

    <TextView
        android:id="@+id/textViewNumber"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TextView"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/guideline2"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:text="1" />

    <TextView
        android:id="@+id/textViewEnglish"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:text="TextView"
        android:textSize="18sp"
        app:layout_constraintBottom_toTopOf="@+id/textViewChinese"
        app:layout_constraintEnd_toStartOf="@+id/guideline3"
        app:layout_constraintHorizontal_bias="0.1"
        app:layout_constraintStart_toStartOf="@+id/guideline2"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/textViewChinese"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:text="TextView"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="@+id/textViewEnglish"
        app:layout_constraintTop_toBottomOf="@+id/textViewEnglish" />

    <ImageView
        android:id="@+id/imageView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="@+id/guideline3"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ic_chevron_right_black_24dp" />
</androidx.constraintlayout.widget.ConstraintLayout>

　　

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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="wrap_content"
    android:background="?attr/selectableItemBackground"
    android:clickable="true"
    android:orientation="vertical">

    <androidx.cardview.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:foreground="?selectableItemBackground"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp">

        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <androidx.constraintlayout.widget.Guideline
                android:id="@+id/guideline4"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:orientation="vertical"
                app:layout_constraintGuide_percent="0.10948905" />

            <androidx.constraintlayout.widget.Guideline
                android:id="@+id/guideline5"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:orientation="vertical"
                app:layout_constraintGuide_percent="0.85" />

            <TextView
                android:id="@+id/textViewNumber"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="TextView"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toStartOf="@+id/guideline4"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                tools:text="1" />

            <TextView
                android:id="@+id/textViewEnglish"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="8dp"
                android:text="TextView"
                android:textSize="24sp"
                app:layout_constraintBottom_toTopOf="@+id/textViewChinese"
                app:layout_constraintEnd_toStartOf="@+id/guideline5"
                app:layout_constraintHorizontal_bias="0.0"
                app:layout_constraintStart_toStartOf="@+id/guideline4"
                app:layout_constraintTop_toTopOf="parent" />

            <TextView
                android:id="@+id/textViewChinese"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginBottom="8dp"
                android:text="TextView"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintStart_toStartOf="@+id/textViewEnglish"
                app:layout_constraintTop_toBottomOf="@+id/textViewEnglish" />

            <ImageView
                android:id="@+id/imageView"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="@+id/guideline5"
                app:layout_constraintTop_toTopOf="parent"
                app:srcCompat="@drawable/ic_chevron_right_black_24dp" />
        </androidx.constraintlayout.widget.ConstraintLayout>
    </androidx.cardview.widget.CardView>
</LinearLayout>

　　

2.创建 适配器 Adapter类 ，继承自  RecylerView.Adapter ，是 RecyclerView 的内容管理器

package com.example.roombasic;

import android.content.Intent;
import android.net.Uri;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

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

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {

    //用来存放数据的列表
    List<Word> allWords = new ArrayList<>();
    boolean use_CellCard; //是否使用 cell_card 这个样式

    public MyAdapter(boolean use_CellCard) {
        this.use_CellCard = use_CellCard;
    }

    public void setAllWords(List<Word> allWords) {
        this.allWords = allWords;
    }

    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        //
        LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());


        //用开关控件，控制不同的样式
        View itemView    ;
        if(use_CellCard)
            itemView = layoutInflater.inflate(R.layout.cell_card,parent,false);
        else
            itemView = layoutInflater.inflate(R.layout.cell_normal,parent,false);


        return new MyViewHolder(itemView);
    }

    //数据绑定
    @Override
    public void onBindViewHolder(@NonNull final MyViewHolder holder, int position) {
        //数据绑定
        final Word word = allWords.get(position);  //通过位置找到内容
        holder.textViewNumber.setText(String.valueOf(position + 1));
        holder.textViewEnglish.setText(word.getWord());
        holder.textViewChinese.setText(word.getChineseMeaning());

        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Uri uri = Uri.parse("http://m.youdao.com/dict?le=eng&q=" + holder.textViewEnglish.getText());

                Intent intent = new Intent(Intent.ACTION_VIEW);
                intent.setData(uri);

                holder.itemView.getContext().startActivity(intent);
            }
        });

    }

    //返回列表数据的总个数
    @Override
    public int getItemCount() {
        return allWords.size();
    }

    // 因为需要管理三个内容，左边的数字，右上英文，右下汉字，所以创建三个值来管理
    // 创建一个属于 Adapter 自身的 ViewHolder
    //加 static 防内存泄漏
    static class MyViewHolder extends RecyclerView.ViewHolder{

        TextView textViewNumber,textViewEnglish,textViewChinese;

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

            textViewNumber = itemView.findViewById(R.id.textViewNumber);
            textViewEnglish = itemView.findViewById(R.id.textViewEnglish);
            textViewChinese = itemView.findViewById(R.id.textViewChinese);
        }
    }
}

　　

　　

3. MainActivity.java 类

package com.example.roombasic;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.CompoundButton;
import android.widget.Switch;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.Observer;
import androidx.lifecycle.SavedStateViewModelFactory;
import androidx.lifecycle.ViewModelProvider;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import java.util.List;





public class MainActivity extends AppCompatActivity {

    //WordDatabase wordDatabase;
    //WordDao wordDao;
    Button buttonInsert,buttonUpdate,buttonClear,buttonDelete;
    TextView textView;
    LiveData<List<Word>> allWordsLive;

    WordViewModel wordViewModel;

    RecyclerView recyclerView;
    MyAdapter myAdapter1; //cell_normal
    MyAdapter myAdapter2; //cell_card   ，这里必须弄2个适配器，要不然一切换数据加载不出来！？？

    Switch aSwitch;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //wordDatabase = Room.databaseBuilder(this,WordDatabase.class,"word_database")
                //.allowMainThreadQueries() //allowMainThreadQueries() 强制允许在主线程运行
        //        .build();

        //wordDao = wordDatabase.getWordDao();

        //wordViewModel = ViewModelProviders


        recyclerView = findViewById(R.id.recyclerView);

        myAdapter1 = new MyAdapter(false);
        myAdapter2 = new MyAdapter(true);

        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(myAdapter1);


        wordViewModel = new ViewModelProvider(this,new SavedStateViewModelFactory(getApplication(),this)).get(WordViewModel.class);


        //allWordsLive = wordDao.getAllWordLive();

        textView = findViewById(R.id.textViewNumber);
        buttonInsert = findViewById(R.id.buttonInsert);
        buttonUpdate = findViewById(R.id.buttonUpdate);
        buttonClear = findViewById(R.id.buttonClear);
        buttonDelete = findViewById(R.id.buttonDelete);
        aSwitch = findViewById(R.id.switch1);


        //开关监听，用的是哪种样式？
        aSwitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                if(aSwitch.isChecked()){
                    recyclerView.setAdapter(myAdapter2);
                }
                else{
                    recyclerView.setAdapter(myAdapter1);
                }
            }
        });

        //利用 LiveData<> 与 observe的onChanged配合，数据自动刷新
        //allWordsLive.observe(this, new Observer<List<Word>>() {
        wordViewModel.getAllWordsLive().observe(this, new Observer<List<Word>>() {
            @Override
            public void onChanged(List<Word> words) {
                //当数据改变时会自动呼叫这个函数
                //String text="";
                /*StringBuilder text = new StringBuilder();
                textView.setText(text); //先将 textView 清空
                for(int i=0;i<words.size();i++){
                    Word word = words.get(i);
                    text.append(word.getId() + ":" + word.getWord() + "=" + word.getChineseMeaning() + "
");

                    textView.setText(text);
                }*/


                myAdapter1.setAllWords(words);
                myAdapter1.notifyDataSetChanged();

                myAdapter2.setAllWords(words);
                myAdapter2.notifyDataSetChanged();
            }
        });


        buttonInsert.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                String[] english = new String[]{"Hello",
                        "World",
                        "Android",
                        "Google",
                        "Studio",
                        "Project",
                        "Database",
                        "RecyclerView",
                        "View",
                        "Value"
                };


                String[] chinese;
                chinese = new String[]{"你好",
                        "世界",
                        "安卓",
                        "谷歌",
                        "工作室",
                        "项目",
                        "数据库",
                        "回收站",
                        "视图",
                        "数值"
                };

                for(int i=0;i<english.length;i++){
                    wordViewModel.insertWords(new Word(english[i],chinese[i]));
                }

            }
        });

        buttonUpdate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("English","英语");
                word.setId(76); //更新是用主键来更新的
                wordViewModel.updateWords(word);
                //wordDao.updateWords(word);
                //new UpdateAsyncTask(wordDao).execute(word);
                //updateView();
            }
        });

        //删除所有的记录
        buttonClear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //wordDao.deleteAllWords();
                //new DeleteAllAsyncTask(wordDao).execute();
                //updateView();
                wordViewModel.deleteAllWords();
            }
        });

        buttonDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word = new Word("English","英语");
                word.setId(76); //删除也是用主键来更新的
                wordViewModel.deleteWords(word);
                //wordDao.deleteWords(word);
                //new DeleteAsyncTask(wordDao).execute(word);
                //updateView();
            }
        });

    }

    /*void updateView(){
        List<Word> list = wordDao.getAllWords();
        String text="";
        textView.setText(text); //先将 textView 清空
        for(int i=0;i<list.size();i++){
            Word word = list.get(i);
            text += word.getId() + ":" + word.getWord() + "=" + word.getChineseMeaning() + "
";

            textView.setText(text);
        }
    }*/




}

　　

 4.细节

  项目每一行设置可点击，在cell_normal.xml 中 设置   android:clickable="true"

  项目点击后，有一个背景， android:foreground="?selectableItemBackground"