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() + "\n");

                    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() + "\n";

            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"

巴特西

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

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