android 使用contentobserver监听数据库内容变化

Love The Way You Lie 2022-08-26 01:18 844阅读 0赞

# android 使用contentobserver监听数据库内容变化 #

在android中经常会用到改变数据库内容后再去使用数据库更新的内容，很多人会重新去query一遍，但是这样的问题就是程序会特别占内存，而且有可能会搂关cursor而导致程序内存未释放等等。其实android内部提供了一种ContentObserver的东西来监听数据库内容的变化。

ContentObserver的构造函数需要一个参数Hanlder，因为ContentObserver内部使用了一个实现Runnable接口的内部类NotificationRunnable，来实现数据库内容的变化。需要使用hanlder去post消息。注册ContentObserver的方法是：getContentResolver().registerContentObserver(uri, notifyForDescendents, observer).  
上面3个参数为：

> uri----Uri类型，是需要监听的数据库的uri.  
> notifyForDescendents---boolean true的话就会监听所有与此uri相关的uri。false的话则是直接特殊的uri才会监听。一般都设置为true.  
> observer-----ContentObserver 就是需要的contentobserver.

初始化一个ContentObserver对象，重载onChange(boolean ),在这个方法里去操作数据库的使用，针对变化后的使用。  
写了一个小demo，可以参考下。提示这种监听方式必须是contentprovider才能使用，因为contentprovider有uri.简单的那种sqlite数据库没有uri是使用不了的。  
下面demo操作的是在一个activityA里点击button跳转至另外一个activityB,在B中点击button往数据库中加数据，加完后关闭B回到A。A的button的文字自动变化设置到数据库中的字符串。

package ty.com.lto;
    
    
    
    import android.app.Activity;
    
    import android.content.Intent;
    
    import android.database.ContentObserver;
    
    import android.os.Bundle;
    
    import android.os.Handler;
    
    import android.view.View;
    
    import android.widget.Button;
    
    
    
    public class ListenDataTest extends Activity{
    
        private Button testBtn;
    
    
    
            @Override
    
            protected void onCreate(Bundle savedInstanceState) {
    
                    super.onCreate(savedInstanceState);
    
                    setContentView(R.layout.listen_data_test);
    
                    getContentResolver().registerContentObserver(DataChangeProvider.CONTENT_URI,
    
                                    true, cob);
    
                    
    
                    testBtn = (Button)findViewById(R.id.test_btn);
    
                    testBtn.setOnClickListener(new View.OnClickListener() {
    
                            
    
                            public void onClick(View v) {
    
                                    Intent in = new Intent(ListenDataTest.this,DataChangeTest.class);
    
                                    startActivity(in);
    
                                    
    
                            }
    
                    });
    
                    
    
            }
    
            
    
            private ContentObserver cob = new ContentObserver(new Handler()) {
    
    
    
                    @Override
    
                    public boolean deliverSelfNotifications() {
    
                            return super.deliverSelfNotifications();
    
                    }
    
    
    
                    @Override
    
                    public void onChange(boolean selfChange) {
    
                            super.onChange(selfChange);
    
                            testBtn.setText(DataUtils.getChangeName(getApplicationContext()));
    
                    }
    
                     
    
             };
    
    
    
            @Override
    
            protected void onDestroy() {
    
                    super.onDestroy();
    
                    getContentResolver().unregisterContentObserver(cob);
    
            }
    
         
    
             
    
    }

package ty.com.lto;
    
    
    
    import android.app.Activity;
    
    import android.content.ContentValues;
    
    import android.content.Intent;
    
    import android.database.ContentObservable;
    
    import android.database.ContentObserver;
    
    import android.os.Bundle;
    
    import android.os.Handler;
    
    import android.view.View;
    
    import android.widget.Button;
    
    
    
    public class DataChangeTest extends Activity{
    
         private Button dataBtn;
    
         DataSqlite mDataSqlite;
    
         @Override
    
         protected void onCreate(Bundle savedInstanceState) {
    
            super.onCreate(savedInstanceState);
    
            setContentView(R.layout.data_change_test);
    
            dataBtn = (Button)findViewById(R.id.data_test_btn);
    
            mDataSqlite = new DataSqlite(this);
    
            dataBtn.setOnClickListener(new View.OnClickListener() {
    
                
    
                public void onClick(View v) {
    
                    ContentValues con = new ContentValues();
    
                    con.put("name", "数据变化了");
    
                    getContentResolver().insert(DataChangeProvider.CONTENT_URI, con);
    
                    finish();
    
                }
    
            });
    
         }
    
    }

package ty.com.lto;
    
     
    
     
    
    import android.content.ContentProvider;
    
    import android.content.ContentUris;
    
    import android.content.ContentValues;
    
    import android.content.Context;
    
    import android.content.UriMatcher;
    
    import android.database.Cursor;
    
    import android.database.SQLException;
    
    import android.database.sqlite.SQLiteDatabase;
    
    import android.database.sqlite.SQLiteOpenHelper;
    
    import android.database.sqlite.SQLiteQueryBuilder;
    
    import android.database.sqlite.SQLiteDatabase.CursorFactory;
    
    import android.net.Uri;
    
    import android.text.TextUtils;
    
     
    
    public class DataChangeProvider extends ContentProvider{
    
        private SQLiteOpenHelper mOpenHelper;
    
        private static final int ALARMS = 1;
    
        private static final int ALARMS_ID = 2;
    
        private static final UriMatcher sURLMatcher = new UriMatcher(UriMatcher.NO_MATCH);
    
        public static final Uri CONTENT_URI = Uri.parse("content://ty.com.lto/test"); 
    
     
    
        static {
    
            sURLMatcher.addURI("ty.com.lto", "test", ALARMS);
    
            sURLMatcher.addURI("ty.com.lto", "test/#", ALARMS_ID);
    
        }
    
        
    
        private static class DatabaseHelper extends SQLiteOpenHelper{
    
             private static final String TEST_DATABASE = "test.db";
    
             private static final int VERSION = 1;
    
             
    
             public DatabaseHelper(Context context) {
    
                 super(context, TEST_DATABASE, null, VERSION);
    
                 // TODO Auto-generated constructor stub
    
             }
    
              
    
     
    
             @Override
    
             public void onCreate(SQLiteDatabase db) {
    
                 String sql = "CREATE TABLE "+"test"+" (" +
    
                         "_id INTEGER PRIMARY KEY," +
    
                         "name TEXT "+ 
    
                          ");";
    
                 db.execSQL(sql);
    
             }
    
     
    
             @Override
    
             public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    
                 String sql = "DROP TABLE IF EXIST "+TEST_DATABASE;
    
                 db.execSQL(sql);
    
                 onCreate(db);
    
             }
    
             
    
        }
    
        
    
        public DataChangeProvider() {
    
        }
    
        
    
        @Override
    
        public int delete(Uri url, String where, String[] whereArgs) {
    
            SQLiteDatabase db = mOpenHelper.getWritableDatabase();
    
            int count;
    
            long rowId = 0;
    
            switch (sURLMatcher.match(url)) {
    
                case ALARMS:
    
                    count = db.delete("test", where, whereArgs);
    
                    break;
    
                case ALARMS_ID:
    
                    String segment = url.getPathSegments().get(1);
    
                    rowId = Long.parseLong(segment);
    
                    if (TextUtils.isEmpty(where)) {
    
                        where = "_id=" + segment;
    
                    } else {
    
                        where = "_id=" + segment + " AND (" + where + ")";
    
                    }
    
                    count = db.delete("test", where, whereArgs);
    
                    break;
    
                default:
    
                    throw new IllegalArgumentException("Cannot delete from URL: " + url);
    
            }
    
     
    
            getContext().getContentResolver().notifyChange(url, null);
    
            return count;
    
        }
    
     
    
        @Override
    
        public String getType(Uri url) {
    
            int match = sURLMatcher.match(url);
    
            switch (match) {
    
                case ALARMS:
    
                    return "vnd.android.cursor.dir/alarms";
    
                case ALARMS_ID:
    
                    return "vnd.android.cursor.item/alarms";
    
                default:
    
                    throw new IllegalArgumentException("Unknown URL");
    
            }
    
        }
    
     
    
        @Override
    
        public Uri insert(Uri url, ContentValues initialValues) {
    
            if (sURLMatcher.match(url) != ALARMS) {
    
                throw new IllegalArgumentException("Cannot insert into URL: " + url);
    
            }
    
     
    
            ContentValues values;
    
            if (initialValues != null) {
    
                values = new ContentValues(initialValues);
    
            } else {
    
                values = new ContentValues();
    
            }
    
                
    
            if (!values.containsKey("name"))
    
                values.put("name", "");
    
     
    
            SQLiteDatabase db = mOpenHelper.getWritableDatabase();
    
            long rowId = db.insert("test", null, values);
    
            if (rowId < 0) {
    
                throw new SQLException("Failed to insert row into " + url);
    
            }
    
            Uri newUrl = ContentUris.withAppendedId(CONTENT_URI, rowId);
    
            getContext().getContentResolver().notifyChange(newUrl, null);
    
            return newUrl;
    
        }
    
     
    
        @Override
    
        public boolean onCreate() {
    
            mOpenHelper = new DatabaseHelper(getContext());
    
            return true;
    
        }
    
     
    
        @Override
    
        public Cursor query(Uri url, String[] projection, String where,
    
                String[] whereArgs, String sortOrder) {
    
            SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
    
            int match = sURLMatcher.match(url);
    
            switch (match) {
    
                case ALARMS:
    
                    qb.setTables("test");
    
                    break;
    
                case ALARMS_ID:
    
                    qb.setTables("test");
    
                    qb.appendWhere("_id=");
    
                    qb.appendWhere(url.getPathSegments().get(1));
    
                    break;
    
                default:
    
                    throw new IllegalArgumentException("Unknown URL " + url);
    
            }
    
     
    
            SQLiteDatabase db = mOpenHelper.getReadableDatabase();
    
            Cursor cur = qb.query(db, projection, where, whereArgs,null, null, sortOrder);
    
            if (cur != null) {
    
                cur.setNotificationUri(getContext().getContentResolver(), url);
    
                 
    
            } 
    
            return cur;
    
        }
    
     
    
        @Override
    
        public int update(Uri url, ContentValues values, String where,String[] whereArgs) {
    
            int count;
    
            long rowId = 0;
    
            int match = sURLMatcher.match(url);
    
            SQLiteDatabase db = mOpenHelper.getWritableDatabase();
    
            switch (match) {
    
                case ALARMS_ID: {
    
                    String segment = url.getPathSegments().get(1);
    
                    rowId = Long.parseLong(segment);
    
                    count = db.update("test", values, "_id=" + rowId, null);
    
                    break;
    
                }
    
                default: {
    
                    throw new UnsupportedOperationException(
    
                            "Cannot update URL: " + url);
    
                }
    
            }
    
            getContext().getContentResolver().notifyChange(url, null);
    
            return count;
    
        }
    
     
    
    }

<?xml version="1.0" encoding="utf-8"?>
    
    <manifest xmlns:android="http://schemas.android.com/apk/res/android"
    
          package="ty.com.lto"
    
          android:versionCode="1"
    
          android:versionName="1.0"
    
          >
    
        <application android:icon="@drawable/icon" android:label="@string/app_name">
    
        <provider android:name="DataChangeProvider" android:authorities="ty.com.lto"/>
    
            <activity android:name=".ListenDataTest"
    
                      android:label="@string/app_name">
    
                <intent-filter>
    
                    <action android:name="android.intent.action.MAIN" />
    
                    <category android:name="android.intent.category.LAUNCHER" />
    
                </intent-filter>
    
            </activity>
    
        <activity android:name=".DataChangeTest" android:label="@string/app_name"/>
    
        </application>
    
    <uses-permission android:name="android.permission.INTERNET"/>
    
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
    
    
    
    </manifest>

**转载自：**[**http://dev.10086.cn/cmdn/bbs/viewthread.php?tid=37427&extra=page%3D1%26amp%3Bfilter%3Dtype%26amp%3Btypeid%3D67**][http_dev.10086.cn_cmdn_bbs_viewthread.php_tid_37427_extra_page_3D1_26amp_3Bfilter_3Dtype_26amp_3Btypeid_3D67]

[http_dev.10086.cn_cmdn_bbs_viewthread.php_tid_37427_extra_page_3D1_26amp_3Bfilter_3Dtype_26amp_3Btypeid_3D67]: http://dev.10086.cn/cmdn/bbs/viewthread.php?tid=37427&extra=page%3D1%26amp%3Bfilter%3Dtype%26amp%3Btypeid%3D67