2

我一直在尝试创建应用程序数据库的副本并将其保存到手机的根目录，但没有运气。我的日志去：

第一步

绝地求生

显然if (sd.canWrite())是第一个错误？有人能帮忙吗？我的想法不多了。谢谢 

public void save() {


        File data = Environment.getDataDirectory();
        File sd = new File(Environment.getExternalStorageDirectory().toString());
        sd.mkdirs();
        Log.d("XXXXXXXXXXXXXXXXXXX", "STEP ONE");
        if (sd.canWrite()) {
            Log.d("XXXXXXXXXXXXXXXXXXX", "STEP TWO");
            String currentDBPath = "/data/com.test.example/databases/example_db";
            String backupDBPath = "/mytest" + "version_two" + ".db";
            File currentDB = new File(data, currentDBPath);
            File backupDB = new File(sd, backupDBPath);
            Log.d("XXXXXXXXXXXXXXXXXXX", "STEP THREE");
            if (currentDB.exists()) {
                Log.d("XXXXXXXXXXXXXXXXXXX", "STEP FOUR");
                FileChannel src;
                try {
                    Log.d("XXXXXXXXXXXXXXXXXXX", "STEP FIVE");
                    src = new FileInputStream(currentDB).getChannel();
                    FileChannel dst = new FileOutputStream(backupDB)
                            .getChannel();
                    try {
                        Log.d("XXXXXXXXXXXXXXXXXXX", "STEP SIX");
                        dst.transferFrom(src, 0, src.size());
                        src.close();
                        dst.close();
                    } catch (IOException e) {
                        Log.d("XXXXXXXXXXXXXXXXXXX", "STEP ONE DEAD");
                        e.printStackTrace();
                    }
                } catch (FileNotFoundException e) {
                    Log.d("XXXXXXXXXXXXXXXXXXX", "STEP TWO DEAD");
                    e.printStackTrace();
                }
            }
        }else{
            Log.d("XXXXXXXXXXXXXXXXXXX", "STEP DEAD");
        }

    }

我的清单剪辑 - 我不知道怎么android:allowBackup="true"到那里 

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity

在模拟器输出上：

01-13 14:16:13.082: D/XXXXXXXXXXXXXXXXXXX(30105): STEP ONE
01-13 14:16:13.082: D/XXXXXXXXXXXXXXXXXXX(30105): STEP DEAD

在设备输出上：

01-13 14:16:13.082: D/XXXXXXXXXXXXXXXXXXX(30105): STEP ONE
01-13 14:16:13.082: D/XXXXXXXXXXXXXXXXXXX(30105): STEP TWO
01-13 14:16:13.082: D/XXXXXXXXXXXXXXXXXXX(30105): STEP THREE
01-13 14:16:13.082: D/XXXXXXXXXXXXXXXXXXX(30105): STEP FOUR
01-13 14:16:13.082: D/XXXXXXXXXXXXXXXXXXX(30105): STEP FIVE
01-13 14:16:13.090: D/XXXXXXXXXXXXXXXXXXX(30105): STEP SIX
4

1 回答 1

1 
 File sd = new File(Environment.getExternalStorageDirectory().toString());

好吧，既然 Environment.getExternalStorageDirectory() 返回一个文件，你不需要创建一个新实例。你可以这样改变它：

 File sd = Environment.getExternalStorageDirectory();
  • sd.mkdirs();/肯定会失败，因为您在and中没有写权限， 并且/mnt指向的目录也sd应该已经退出
  • 写权限 - WRITE_EXTERNAL_STORAGE：您是否将其添加到您的 AndroidManifex 文件中？可能 canWrite() 返回 false 因为您忘记添加权限
于 2013-01-13T09:31:04.320 回答