Room----Android数据库(SQLite)

Posted 2020-11-25 嘉禾旧木

1.要想使用Room首先需要在build.grade中添加依赖

 1     dependencies {
 2       def room_version = "2.2.2"
 3 
 4       implementation "androidx.room:room-runtime:$room_version"
 5       annotationProcessor "androidx.room:room-compiler:$room_version" // For Kotlin use kapt instead of annotationProcessor
 6 
 7       // optional - Kotlin Extensions and Coroutines support for Room
 8       implementation "androidx.room:room-ktx:$room_version"
 9 
10       // optional - RxJava support for Room
11       implementation "androidx.room:room-rxjava2:$room_version"
12 
13       // optional - Guava support for Room, including Optional and ListenableFuture
14       implementation "androidx.room:room-guava:$room_version"
15 
16       // Test helpers
17       testImplementation "androidx.room:room-testing:$room_version"
18     }
19     

 

2.数据库可视化工具可以选择DB Browser for SQLite，具体请点击下方链接进行下载

http://www.sqlitebrowser.org/

 

具体案例(对Word实体进行增删改)

使用ViewModel，LiveData，Room等工具。

 

1.界面设计

• 上方是一个ScrollView（数据多的时候可滑动),ScrollView内有一个TextView
• 下方是四个按键，分别代表，插入、删除、清空、修改

activity_main.xml代码如下：

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
 3     xmlns:app="http://schemas.android.com/apk/res-auto"
 4     xmlns:tools="http://schemas.android.com/tools"
 5     android:layout_width="match_parent"
 6     android:layout_height="match_parent"
 7     tools:context=".MainActivity">
 8 
 9     <androidx.constraintlayout.widget.Guideline
10         android:id="@+id/guideline"
11         android:layout_width="wrap_content"
12         android:layout_height="wrap_content"
13         android:orientation="horizontal"
14         app:layout_constraintGuide_percent="0.6" />
15 
16     <ScrollView
17         android:layout_width="0dp"
18         android:layout_height="0dp"
19         app:layout_constraintBottom_toTopOf="@+id/guideline"
20         app:layout_constraintEnd_toEndOf="parent"
21         app:layout_constraintStart_toStartOf="parent"
22         app:layout_constraintTop_toTopOf="parent">
23 
24         <TextView
25             android:id="@+id/textView"
26             android:layout_width="match_parent"
27             android:layout_height="wrap_content"
28             android:text="TextView"
29             android:textSize="24sp" />
30     </ScrollView>
31 
32     <Button
33         android:id="@+id/buttonInsert"
34         android:layout_width="wrap_content"
35         android:layout_height="wrap_content"
36         android:text="insert"
37         app:layout_constraintBottom_toBottomOf="parent"
38         app:layout_constraintEnd_toStartOf="@+id/buttonUpdate"
39         app:layout_constraintHorizontal_bias="0.5"
40         app:layout_constraintStart_toStartOf="parent"
41         app:layout_constraintTop_toTopOf="@+id/guideline"
42         app:layout_constraintVertical_bias="0.25" />
43 
44     <Button
45         android:id="@+id/buttonUpdate"
46         android:layout_width="wrap_content"
47         android:layout_height="wrap_content"
48         android:text="update"
49         app:layout_constraintBottom_toBottomOf="@+id/buttonInsert"
50         app:layout_constraintEnd_toEndOf="parent"
51         app:layout_constraintHorizontal_bias="0.5"
52         app:layout_constraintStart_toEndOf="@+id/buttonInsert"
53         app:layout_constraintTop_toTopOf="@+id/buttonInsert" />
54 
55     <Button
56         android:id="@+id/buttonClear"
57         android:layout_width="wrap_content"
58         android:layout_height="wrap_content"
59         android:text="clear"
60         app:layout_constraintBottom_toBottomOf="@+id/buttonDelete"
61         app:layout_constraintEnd_toStartOf="@+id/buttonDelete"
62         app:layout_constraintHorizontal_bias="0.5"
63         app:layout_constraintStart_toStartOf="parent"
64         app:layout_constraintTop_toTopOf="@+id/buttonDelete" />
65 
66     <Button
67         android:id="@+id/buttonDelete"
68         android:layout_width="wrap_content"
69         android:layout_height="wrap_content"
70         android:text="delete"
71         app:layout_constraintBottom_toBottomOf="parent"
72         app:layout_constraintEnd_toEndOf="parent"
73         app:layout_constraintHorizontal_bias="0.5"
74         app:layout_constraintStart_toEndOf="@+id/buttonClear"
75         app:layout_constraintTop_toBottomOf="@+id/buttonUpdate" />
76 </androidx.constraintlayout.widget.ConstraintLayout>

View Code

以为是学习新的知识，所以不是太注重规定，导致 一些地方写的不是很规范。

 

2.创建实体(Entity)

 1 package com.example.roombasic;
 2 
 3 import androidx.room.ColumnInfo;
 4 import androidx.room.Entity;
 5 import androidx.room.PrimaryKey;
 6 
 7 @Entity
 8 public class Word {
 9     @PrimaryKey(autoGenerate = true)
10     private int id;
11     @ColumnInfo(name = "english_word")
12     private String word;
13     @ColumnInfo(name = "chinese_meaning")
14     private String chineseMeaning;
15 
16     public Word(String word, String chineseMeaning) {
17         this.word = word;
18         this.chineseMeaning = chineseMeaning;
19     }
20 
21     public int getId() {
22         return id;
23     }
24 
25     public void setId(int id) {
26         this.id = id;
27     }
28 
29     public String getWord() {
30         return word;
31     }
32 
33     public void setWord(String word) {
34         this.word = word;
35     }
36 
37     public String getChineseMeaning() {
38         return chineseMeaning;
39     }
40 
41     public void setChineseMeaning(String chineseMeaning) {
42         this.chineseMeaning = chineseMeaning;
43     }
44 }

 

3.创建Dao

 1 package com.example.roombasic;
 2 
 3 import androidx.lifecycle.LiveData;
 4 import androidx.room.Dao;
 5 import androidx.room.Delete;
 6 import androidx.room.Insert;
 7 import androidx.room.Query;
 8 import androidx.room.Update;
 9 
10 import java.util.List;
11 
12 @Dao
13 public interface WordDao {
14     @Insert
15     void insertWords(Word... words);
16 
17     @Update
18     void updateWords(Word... words);
19 
20     @Delete
21     void deleteWords(Word... words);
22 
23     @Query("DElETE FROM WORD")
24     void deleteAllWords();
25 
26     @Query("SELECT * FROM WORD ORDER BY ID DESC ")
27     LiveData<List<Word>> getAllWordsLive();
28 }

 

4.创建database

 1 package com.example.roombasic;
 2 
 3 import android.content.Context;
 4 
 5 import androidx.room.Database;
 6 import androidx.room.Room;
 7 import androidx.room.RoomDatabase;
 8 
 9 @Database(entities = {Word.class}, version = 1, exportSchema = false)
10 public abstract class WordDataBase extends RoomDatabase {
11     private static WordDataBase INSTANCE;
12 
13     static synchronized WordDataBase getDatabase(Context context) {
14         if (INSTANCE == null) {
15             INSTANCE = Room.databaseBuilder(context.getApplicationContext(), WordDataBase.class, "word_database").build();
16         }
17         return INSTANCE;
18     }
19     public abstract WordDao getWordDao();
20 }

 

5.创建ViewModel绑定数据

 1 package com.example.roombasic;
 2 
 3 import android.app.Application;
 4 import android.os.AsyncTask;
 5 
 6 import androidx.annotation.NonNull;
 7 import androidx.lifecycle.AndroidViewModel;
 8 import androidx.lifecycle.LiveData;
 9 
10 import java.util.List;
11 
12 public class WordViewModel extends AndroidViewModel {
13     private WordDao wordDao;
14     private LiveData<List<Word>> allWordsLive;
15 
16     public WordViewModel(@NonNull Application application) {
17         super(application);
18         WordDataBase wordDataBase = WordDataBase.getDatabase(application);
19         wordDao = wordDataBase.getWordDao();
20         allWordsLive = wordDao.getAllWordsLive();
21     }
22 
23     public LiveData<List<Word>> getAllWordsLive() {
24         return allWordsLive;
25     }
26 
27     void insertWords(Word... words) {
28         new InsertAsyncTask(wordDao).execute(words);
29     }
30 
31     void updateWords(Word... words) {
32         new UpdateAsyncTask(wordDao).execute(words);
33     }
34 
35     void deleteWords(Word... words) {
36         new DeleteAsyncTask(wordDao).execute(words);
37     }
38 
39     void deleteAllWords(Word... words) {
40         new DeleteAllAsyncTask(wordDao).execute();
41     }
42 
43     static class InsertAsyncTask extends AsyncTask<Word, Void, Void> {
44         private WordDao wordDao;
45 
46         public InsertAsyncTask(WordDao wordDao) {
47             this.wordDao = wordDao;
48         }
49 
50         @Override
51         protected Void doInBackground(Word... words) {
52             wordDao.insertWords(words);
53             return null;
54         }
55     }
56 
57     static class UpdateAsyncTask extends AsyncTask<Word, Void, Void> {
58         private WordDao wordDao;
59 
60         public UpdateAsyncTask(WordDao wordDao) {
61             this.wordDao = wordDao;
62         }
63 
64         @Override
65         protected Void doInBackground(Word... words) {
66             wordDao.updateWords(words);
67             return null;
68         }
69     }
70 
71     static class DeleteAsyncTask extends AsyncTask<Word, Void, Void> {
72         private WordDao wordDao;
73 
74         public DeleteAsyncTask(WordDao wordDao) {
75             this.wordDao = wordDao;
76         }
77 
78         @Override
79         protected Void doInBackground(Word... words) {
80             wordDao.deleteWords(words);
81             return null;
82         }
83     }
84 
85     static class DeleteAllAsyncTask extends AsyncTask<Void, Void, Void> {
86         private WordDao wordDao;
87 
88         public DeleteAllAsyncTask(WordDao wordDao) {
89             this.wordDao = wordDao;
90         }
91 
92         @Override
93         protected Void doInBackground(Void... voids) {
94             wordDao.deleteAllWords();
95             return null;
96         }
97     }
98 }

 

6.在MainActivity.java中添加按键监听

 1 package com.example.roombasic;
 2 
 3 import android.os.Bundle;
 4 import android.view.View;
 5 import android.widget.Button;
 6 import android.widget.TextView;
 7 
 8 import androidx.appcompat.app.AppCompatActivity;
 9 import androidx.lifecycle.Observer;
10 import androidx.lifecycle.ViewModelProviders;
11 
12 import java.util.List;
13 
14 public class MainActivity extends AppCompatActivity {
15     TextView textView;
16     Button buttonInsert, buttonDelete, buttonUpdate, buttonClear;
17     WordViewModel wordViewModel;
18 
19     @Override
20     protected void onCreate(Bundle savedInstanceState) {
21         super.onCreate(savedInstanceState);
22         setContentView(R.layout.activity_main);
23         wordViewModel = ViewModelProviders.of(this).get(WordViewModel.class);
24         textView = findViewById(R.id.textView);
25         wordViewModel.getAllWordsLive().observe(this, new Observer<List<Word>>() {
26             @Override
27             public void onChanged(List<Word> words) {
28                 StringBuilder text = new StringBuilder();
29                 for (int i = 0; i < words.size(); i++) {
30                     Word word = words.get(i);
31                     text.append(word.getId()).append(":").append(word.getWord()).append("=").append(word.getChineseMeaning()).append("
");
32                 }
33                 textView.setText(text.toString());
34             }
35         });
36 
37         buttonInsert = findViewById(R.id.buttonInsert);
38         buttonClear = findViewById(R.id.buttonClear);
39         buttonDelete = findViewById(R.id.buttonDelete);
40         buttonUpdate = findViewById(R.id.buttonUpdate);
41 
42         buttonInsert.setOnClickListener(new View.OnClickListener() {
43             @Override
44             public void onClick(View v) {
45                 Word word1 = new Word("Hello", "你好！");
46                 Word word2 = new Word("World", "世界！");
47                 wordViewModel.insertWords(word1,word2);
48             }
49         });
50 
51         buttonClear.setOnClickListener(new View.OnClickListener() {
52             @Override
53             public void onClick(View v) {
54                 wordViewModel.deleteAllWords();
55             }
56         });
57 
58         buttonUpdate.setOnClickListener(new View.OnClickListener() {
59             @Override
60             public void onClick(View v) {
61                 Word word = new Word("Hi", "你好啊！");
62                 word.setId(9);
63                 wordViewModel.updateWords(word);
64             }
65         });
66 
67         buttonDelete.setOnClickListener(new View.OnClickListener() {
68             @Override
69             public void onClick(View v) {
70                 Word word = new Word("Hi", "你好啊！");
71                 word.setId(7);
72                 wordViewModel.deleteWords(word);
73             }
74         });
75     }
76 }

该实例中修改与删除使用主键进行的，以后会进行修改与完善 。

暂时只学习了一点皮毛，后续会增加一些新的内容。