Question

我正在使用SQLLite作为Android的基于phonegap的应用程序。我面临的问题是，只要应用程序处于打开状态，我就可以获取我存储在local.db文件中的任何数据。例如，我有一个设置功能，用户可以保存他/她的设置，然后进入db.Now我面临的问题是，我无法获取用户在应用程序关闭后保存的数据，I只要应用程序处于打开状态，就可以获取数据。所以问题是数据库不是持久的。任何人都可以告诉如何在应用程序关闭时将数据存储在内存中吗？

这是我的mainActivity文件

public class Demo extends CordovaActivity 
{
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        super.init();
        super.loadUrl(Config.getStartUrl());            
        try {
            String pName = this.getClass().getPackage().getName();
            this.copy("Databases.db", "/data/data/" + pName + "/app_database/");
            this.copy("0000000000000001.db", "/data/data/" + pName
                    + "/app_database/file__0/");
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    void copy(String file, String folder) throws IOException {

        File CheckDirectory;
        CheckDirectory = new File(folder);
        if (!CheckDirectory.exists()) {
            CheckDirectory.mkdir();
            InputStream in = getApplicationContext().getAssets().open(file);
        OutputStream out = new FileOutputStream(folder + file);

        // Transfer bytes from in to out
        byte[] buf = new byte[1024];
        int len;
        while ((len = in.read(buf)) > 0)
            out.write(buf, 0, len);
        in.close();
        out.close();
        }
    }
}

这些是我给出的权限： -

        <uses-permission android:name="android.permission.INTERNET" />
  <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.VIBRATE" />
       <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
        <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

将复制代码移动到 NigelK 所提及的if条件后完成了诀窍。但卸载构建并创建新构建后，给出了以下错误： -

01-10 16:11:34.466: E/SQLiteLog(29253): (1) no such table: CacheGroups
01-10 16:11:34.466: D/WebKit(29253): ERROR: 
01-10 16:11:34.466: D/WebKit(29253): Application Cache Storage: failed to execute statement "DELETE FROM CacheGroups" error "no such table: CacheGroups"
01-10 16:11:34.466: D/WebKit(29253): external/webkit/Source/WebCore/loader/appcache/ApplicationCacheStorage.cpp(558) : bool WebCore::ApplicationCacheStorage::executeSQLCommand(const WTF::String&)
01-10 16:11:34.466: E/SQLiteLog(29253): (1) no such table: Caches
01-10 16:11:34.466: D/WebKit(29253): ERROR: 
01-10 16:11:34.466: D/WebKit(29253): Application Cache Storage: failed to execute statement "DELETE FROM Caches" error "no such table: Caches"
01-10 16:11:34.466: D/WebKit(29253): external/webkit/Source/WebCore/loader/appcache/ApplicationCacheStorage.cpp(558) : bool WebCore::ApplicationCacheStorage::executeSQLCommand(const WTF::String&)
01-10 16:11:34.466: E/SQLiteLog(29253): (1) no such table: Origins
01-10 16:11:34.466: D/WebKit(29253): ERROR: 
01-10 16:11:34.466: D/WebKit(29253): Application Cache Storage: failed to execute statement "DELETE FROM Origins" error "no such table: Origins"
01-10 16:11:34.466: D/WebKit(29253): external/webkit/Source/WebCore/loader/appcache/ApplicationCacheStorage.cpp(558) : bool WebCore::ApplicationCacheStorage::executeSQLCommand(const WTF::String&)
01-10 16:11:34.476: E/SQLiteLog(29253): (1) no such table: DeletedCacheResources

关于如何处理这个问题的任何想法？

Answer 1

您的数据库是持久的，问题是每次您的应用程序启动时，onCreate（）中对copy（）方法的调用会再次使用Assets中保存的副本覆盖数据库。我想你只想制作一次这样的副本。一种方法是仅在目标目录尚不存在时才执行复制：

if (!CheckDirectory.exists()) {
    CheckDirectory.mkdir();
    ...move the copy code inside this if block
}

或者您可以在共享首选项中存储标志，并在制作副本时将其设置为true。在onCreate中，如果该标志为false，则仅执行副本。

编辑：

使用共享偏好标记：

on onCreate：

SharedPreferences sp = getSharedPreferences("MYPREFS", Activity.MODE_PRIVATE);

//If no shared prefs exist, e.g. first install, it doesn't matter - the following will return false as a default
Boolean database_copied = sp.getBoolean("database_copied", false);

if (!database_copied)
{
    try {
        String pName = this.getClass().getPackage().getName();
        this.copy("Databases.db", "/data/data/" + pName + "/app_database/");
        this.copy("0000000000000001.db", "/data/data/" + pName
                + "/app_database/file__0/");
        SharedPreferences.Editor editor = sp.edit();
        editor.putBoolean("database_copied", true);
        editor.apply();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Answer 2

只需创建一个空白数据库并将其替换为新资产DB ..

Thread getData = new Thread() {
        public void run() {

            Data.qh = new QueryHandler(mContext); // for creating a blank DB
            DB_PATH = getDatabasePath("htest.sqlite").getAbsolutePath(); // get the path of blank DB
            copyDataBase(mContext);

        };
    };


void copyDataBase(Context mContext) {

        try {

            String outFileName = DB_PATH;

            OutputStream myOutput = new FileOutputStream(outFileName);

            byte[] buffer = new byte[1024];
            int length;

            InputStream myInput = mContext.getAssets().open("htest.sqlite");
            while ((length = myInput.read(buffer)) > 0) {
                myOutput.write(buffer, 0, length);
            }
            myInput.close();

            myOutput.flush();
            myOutput.close();
        } catch (Exception ex) {
            ex.printStackTrace();
        }

    }

Answer 3

下面是示例代码，这是在Javascript调用的html页面中实现的

function onDeviceReady() 
{
  var db = window.openDatabase("Database", "1.0", "Cordova Demo", 200000);
  db.transaction(populateDB, errorCB, successCB);
}

然后我们必须在Table中填充数据，调用方法

function populateDB(tx) 
{
  var id=$('#id').val();
  var firstname=$('#firstname').val();        
  tx.executeSql('CREATE TABLE IF NOT EXISTS DEMO (id unique, firstname)');
  tx.executeSql('INSERT INTO DEMO (id, firstname) VALUES (?, ?)', [id, firstname]);
}

要保存数据，请执行以下任何事件

<button class="button" id="clickMe" onclick="onDeviceReady();" >Save</button>

使用Phonegap从SQLite db for Android填充数据

3 个答案: