从资产文件夹复制数据库[重复]

我正在创建一个使用现有 sqlite 数据库的字典应用程序。我已将数据库放置在资产文件夹中，并在应用程序首次启动时使用以下代码来复制数据库。 （我借用了这个想法this http://www.reigndesign.com/blog/using-your-own-sqlite-database-in-android-applications/ post)

数据库助手.java

public class DatabaseHelper {

private static String DB_PATH = "";
private static String DB_NAME = "abc.sqlite";
private SQLiteDatabase myDatabase;
private Context myContext;

public DatabaseHelper(Context context) {

    myContext = context;

    if (android.os.Build.VERSION.SDK_INT >= 17)
        DB_PATH = context.getApplicationInfo().dataDir + "/databases/";
    else
        DB_PATH = "/data/data/" + context.getPackageName() + "/databases/";
    Log.d("path", DB_PATH);
}

public void copyDatabase() {

        InputStream myInput;
        OutputStream outStream;
        try {
            myInput = myContext.getAssets().open(DB_NAME);
            String file = DB_PATH + DB_NAME;
            outStream = new FileOutputStream(file);

            byte[] buffer = new byte[1024];
            int length = 0;
            while ((length = myInput.read(buffer)) >= 0) {
                outStream.write(buffer, 0, length);             
            }
            outStream.flush();
            myInput.close();
            outStream.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

然后我调用上面的copyDatabase()方法形成我的MainActivity。这是代码。

public class MainActivity extends Activity {
    DatabaseHelper myDbHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.layout);
        myDbHelper = new DatabaseHelper(getApplicationContext());
        myDbHelper.copyDatabase();


    }

}

但问题是Android不复制数据库。我使用了 Log 工具，发现 while 循环从未运行。 这段代码有什么问题。 谢谢。

如下更改 while 循环：

除了你的条件之外>=大于或等于将其更改为仅>比...更棒

while ((length = myInput.read(buffer)) > 0) {
            outStream.write(buffer, 0, length);             
        }

尝试下面的代码，它会像魅力一样为您工作。

public class DataBaseHelper extends SQLiteOpenHelper {
    private Context mycontext;
    private String DB_PATH; 

    private static String DB_NAME = "abc.sqlite";
    public SQLiteDatabase myDataBase;


    public DataBaseHelper(Context context) throws IOException {
        super(context,DB_NAME,null,1);
        this.mycontext=context;
        boolean dbexist = checkdatabase();
        if (dbexist) {
              opendatabase(); 
        } else {
            System.out.println("Database doesn't exist");
            createdatabase();
        }
    }

    public void createdatabase() throws IOException {
        boolean dbexist = checkdatabase();
        if(!dbexist) {
            this.getReadableDatabase();
            try {
                copydatabase();
            } catch(IOException e) {
                throw new Error("Error copying database");
            }
        }
    }   

    private boolean checkdatabase() {

        boolean checkdb = false;
        try {
            String myPath = DB_PATH + DB_NAME;
            File dbfile = new File(myPath);
            checkdb = dbfile.exists();
        } catch(SQLiteException e) {
            System.out.println("Database doesn't exist");
        }
        return checkdb;
    }

    private void copydatabase() throws IOException {
        //Open your local db as the input stream
        InputStream myinput = mycontext.getAssets().open(DB_NAME);

        // Path to the just created empty db
        String outfilename = DB_PATH + DB_NAME;

        //Open the empty db as the output stream
        OutputStream myoutput = new FileOutputStream(outfilename);

        // transfer byte to inputfile to outputfile
        byte[] buffer = new byte[1024];
        int length;
        while ((length = myinput.read(buffer))>0) {
            myoutput.write(buffer,0,length);
        }

        //Close the streams
        myoutput.flush();
        myoutput.close();
        myinput.close();
    }

    public void opendatabase() throws SQLException {
        //Open the database
        String mypath = DB_PATH + DB_NAME;
        myDataBase = SQLiteDatabase.openDatabase(mypath, null, SQLiteDatabase.OPEN_READWRITE);
    }

    public synchronized void close() {
        if(myDataBase != null) {
            myDataBase.close();
        }
        super.close();
    }

}

In your MainActivity您现在需要创建您的实例DatabaseHelper其他班级将自行管理。

public class MainActivity extends Activity {
    DatabaseHelper myDbHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.layout);
        myDbHelper = new DatabaseHelper(MainActivity.this);
      }

}