安卓简单的监测数据库的变化

介绍：

用于监测数据库的变化，因此需要创建两个程序，一个用与操作数据库，一个用于监测数据库变化。当数据库发生变化时，监测数据库的程序会立即响应。接下来创建操作数据库的程序

布局：

1. 所有包
   
2. 操作数据库
   
3. 监测数据库的变化
   

代码：

1. 创建项目：
   项目名：ContentObserverDB
   
2. activity_main.xml

3.  MainActivity
    

   package com.e.contentobserverdb.activity;
   
   import androidx.appcompat.app.AppCompatActivity;
   
   import android.content.ContentResolver;
   import android.content.ContentValues;
   import android.database.Cursor;
   import android.database.sqlite.SQLiteDatabase;
   import android.net.Uri;
   import android.os.Bundle;
   import android.os.ConditionVariable;
   import android.util.Log;
   import android.view.View;
   import android.widget.Button;
   import android.widget.Toast;
   
   import com.e.contentobserverdb.R;
   import com.e.contentobserverdb.others.PersonDBOpenHelper;
   
   import java.util.ArrayList;
   import java.util.Currency;
   import java.util.HashMap;
   import java.util.List;
   import java.util.Map;
   import java.util.Random;
   
   public class MainActivity extends AppCompatActivity implements View.OnClickListener {
       private ContentResolver resolver;
       private Uri uri;
       private Button btnInsert;
       private Button btnUpdate;
       private Button btnDelete;
       private Button btnSelect;
       private ConditionVariable variable;
       private ContentValues values;
   
       @Override
       protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);
           setContentView(R.layout.activity_main);
   
           initView();//初始化界面
           createDB();//创建数据库
       }
   
   
       //初始化界面
       private void createDB() {
           //创建数据库并向info表中添加3条数据
           PersonDBOpenHelper helper = new PersonDBOpenHelper(this);
           SQLiteDatabase db = helper.getWritableDatabase();
           for (int i = 0; i <3; i++){
               ContentValues values = new ContentValues();
               values.put("name","itcast"+i);
               db.insert("info",null,values);
           }
           db.close();
   
       }
       //创建数据库
       private void initView() {
           btnInsert = (Button) findViewById(R.id.btu_insert);
           btnDelete = (Button) findViewById(R.id.btu_delete);
           btnSelect = (Button) findViewById(R.id.btu_select);
           btnUpdate = (Button) findViewById(R.id.btu_update);
           btnInsert.setOnClickListener(this);
           btnDelete.setOnClickListener(this);
           btnSelect.setOnClickListener(this);
           btnUpdate.setOnClickListener(this);
       }
   
       @Override
       public void onClick(View v) {
           //得到一个内容提供者的解析对象
            resolver = getContentResolver();
           //新加一个uri路径，参数是string类型的
           uri = Uri.parse("content://cn.contentobserverdb/info");
           //新建一个ContentValues对象，该对象以key-values的形式来添加记录到数据库中
           values = new ContentValues();
           switch (v.getId()){
               case R.id.btu_insert:
                   Random random = new Random();
                   //random.nextInt(10)随机生成一个（0，10）的正数
                   values.put("name","新增"+random.nextInt(10));
                   Uri newuri = resolver.insert(uri,values);
                   Toast.makeText(this,"添加成功",Toast.LENGTH_SHORT).show();
                   Log.i("数据库应用","添加");
                   break;
               case R.id.btu_delete:
                   //返回删除数据的条目数
                   //int deleteCount = resolver.delete(uri,"name=?,new string[]){"新增0"}};
                   int deleteCount = resolver.delete(uri,null,null);
                   Toast.makeText(this,"成功删除了" + deleteCount + "行",Toast.LENGTH_SHORT).show();
                   Log.i("数据库应用","删除");
                   break;
               case R.id.btu_select:
                   List> data = new ArrayList<>();
                   //返回查询结果，是一个指向结果的游标
                   Cursor cursor = resolver.query(uri,new String[]{"_id","name"},null,null,null);
                   while (cursor.moveToNext()) {
                       Map map = new HashMap<>();
                       map.put("_id",cursor.getString(0));
                       map.put("name",cursor.getString(1));
                       data.add(map);
                   }
                   //关闭游标，释放资源
                   cursor.close();
                   Log.i("数据库应用","查询结果："+data.toString());
                   break;
               case R.id.btu_update:
                   //将数据库info表中那么为itcase1这条记录update_itcast
                   values.put("name","update_itcast");
                   int updateCount = resolver.update(uri,values,"name=?",new String[]{"更新"});
                   if (updateCount!=0){
                       Toast.makeText(this,"成功更新了"+updateCount+"行",Toast.LENGTH_SHORT).show();
                       Log.i("数据库应用","更新");
                   }else {
                       Toast.makeText(this,"没有好到更新的数据",Toast.LENGTH_SHORT).show();
                   }
                   break;
   
           }
       }
   }

4. PersonDBOpenHelper

   package com.e.contentobserverdb.others;
   
   import android.content.ContentProvider;
   import android.content.ContentValues;
   import android.content.Context;
   import android.database.Cursor;
   import android.database.sqlite.SQLiteDatabase;
   import android.database.sqlite.SQLiteOpenHelper;
   import android.net.Uri;
   
   public class PersonDBOpenHelper extends SQLiteOpenHelper {
       //构造方法，调用此方法新建一个person.db的数据库并返回一个数据库帮助类的对象
       public PersonDBOpenHelper(Context context) {
           super(context,"person.db",null,1);
       }
       @Override
       public void  onCreate(SQLiteDatabase db) {
           // TODO: Implement this to initialize your content provider on startup.
           // 创建该数据库的同时新建一个info表，表中有_id,name这两个字段
           db.execSQL("create table info(_id integer primary key autoincrement,name varchar(20))");
       }
   
       @Override
       public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {
       }
   
   }

5. PersonProvder

   package com.e.contentobserverdb.others;
   
   import android.content.ContentProvider;
   import android.content.ContentUris;
   import android.content.ContentValues;
   import android.content.UriMatcher;
   import android.database.Cursor;
   import android.database.sqlite.SQLiteDatabase;
   import android.net.Uri;
   
   public class PersonProvider extends ContentProvider {
       //定义一个uri路径的匹配器，如果路径匹配不成功返回-1
       private static UriMatcher mUriMatcher = new UriMatcher(-1);
       //匹配路径成功时的返回码
       private static final int SUCCESS = 1;
       //数据库操作类的对象
       private PersonDBOpenHelper helper;
       //添加路径匹配器的规则
       static {
           mUriMatcher.addURI("cn.contentobserverdb","info",SUCCESS);
       }
   
       public PersonProvider() {
       }
   
       @Override
       //删除数据操纵作
       public int delete(Uri uri, String selection, String[] selectionArgs) {
           // Implement this to handle requests to delete one or more rows.
           int code = mUriMatcher.match(uri);
           if (code == SUCCESS){
               SQLiteDatabase db = helper.getWritableDatabase();
               int count = db.delete("info",selection,selectionArgs);
               //提示数据库的内容变化了
               if (count > 0 ){
                   getContext().getContentResolver().notifyChange(uri,null);
               }
               db.close();
               return count;
           }else {
               throw new UnsupportedOperationException("路径不正确，我是不会让你随便删除数据库的！");
           }
       }
   
       @Override
       public String getType(Uri uri) {
           // TODO: Implement this to handle requests for the MIME type of the data
           // at the given URI.
           return null;
       }
   
       @Override
       //添加数据操作
       public Uri insert(Uri uri, ContentValues values) {
           // TODO: Implement this to handle requests to insert a new row.
           int code = mUriMatcher.match(uri);
           if (code == SUCCESS){
               SQLiteDatabase db = helper.getReadableDatabase();
               long rowId = db.insert("info",null,values);
               if (rowId > 0){
                   Uri insertedUri = ContentUris.withAppendedId(uri,rowId);
                   //提示数据库的内容变化了
                   getContext().getContentResolver().notifyChange(insertedUri ,null);
                   return insertedUri;
               }
               db.close();
               return uri;
           }else {
               throw new UnsupportedOperationException("数据路今年不正确，我是不会给你插入数据的！");
           }
       }
   
       @Override
       //当类容提供者被创键的时候调用
       public boolean onCreate() {
           // TODO: Implement this to initialize your content provider on startup.
           helper = new PersonDBOpenHelper(getContext());
           return false;
       }
   
       @Override
       //查询数据操作
       public Cursor query(Uri uri, String[] projection, String selection,
               String[] selectionArgs, String sortOrder) {
           // TODO: Implement this to handle query requests from clients.
           //匹配查询的uri路径
           int code = mUriMatcher.match(uri);
           if (code == SUCCESS){
               SQLiteDatabase db = helper.getReadableDatabase();
               return db.query("into",projection,selection,selectionArgs,null,null,sortOrder);
           }else {
               throw  new IllegalArgumentException("路径不真确，我们时不会给你提供数据的！");
           }
       }
   
       @Override
       public int update(Uri uri, ContentValues values, String selection,
               String[] selectionArgs) {
           // TODO: Implement this to handle requests to update one or more rows.
           int code = mUriMatcher.match(uri);
           if (code == SUCCESS) {
               SQLiteDatabase db = helper.getWritableDatabase();
               int count = db.update("info",values,selection,selectionArgs);
               //提示数据库的内容变化了
               if (count > 0) {
                   getContext().getContentResolver().notifyChange(uri,null);
               }
               db.close();
               return count;
           }
           else {
               throw new UnsupportedOperationException("Not yet implemented");
           }
       }
   }

运行结果：

1. 效果图
   
2. 点击添加
   1. monitordata结果
      
   2. app结果
      
3. 点击更新
   1. monitordata结果
   2. app结果
4. 点击删除
   1. monitordata结果
   2. app结果
5. 点击查询
   1. monitordata结果
   2. app结果 

自己做出现的错误

（给大家避一下雷）

1. 错误（以解决）
   
   下面时寻找的解决方式
   https://blog.csdn.net/miyuehu/article/details/122840074?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522164933771316781685396605%2522%252C%2522scm%2522%253A%252220140713.130102334.pc%255Fall.%2522%257D&request_id=164933771316781685396605&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~first_rank_ecpm_v1~rank_v31_ecpm-4-122840074.142^v7^pc_search_result_cache,157^v4^control&utm_term=Failed+to+find+Build+Tools+revision+30.0.3&spm=1018.2226.3001.4187http://xn--67qz10c99e8r6a
2. 查询出现的错误（还没解决，如有解决的朋友请联系）