安卓：数据库导出工作在模拟器，而不是手机 [英] Android: database export works on emulator, not on phone

问题描述

我想我的应用程序的数据库导出到SD卡。它的工作原理优秀的仿真器，车针不是我的电话。

I'm trying to export my application's database to SDcard. It works excellent for emulator, bur not for my phone.

    OnClickListener mExportListener = new OnClickListener(){
public void onClick(View v){
    try {
        File sd = Environment.getExternalStorageDirectory();
        File data = Environment.getDataDirectory();
        if (sd.canWrite()) {
            String currentDBPath = "\\data\\com.mypck.myapp\\databases\\database";
            String backupDBPath = "database.db";
            File currentDB = new File(data, currentDBPath);
            File backupDB = new File(sd, backupDBPath);

            if (currentDB.exists()) {
                FileChannel src = new FileInputStream(currentDB).getChannel();
                FileChannel dst = new FileOutputStream(backupDB).getChannel();
                dst.transferFrom(src, 0, src.size());
                src.close();
                dst.close();
            }else{
             String msg = activity.getResources().getString(R.string.something_wrong);        
             Toast toast = Toast.makeText(getApplicationContext(), msg, Toast.LENGTH_LONG);  
             toast.show();
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}
};

本 currentDB.exists（）在手机上返回假的，但我检查了文件 - 它的存在。
什么是错我的电话？

This currentDB.exists() returns false on the phone, but I checked the file - it exists. What is wrong with my phone?

推荐答案

您提供文件错误的参数。从Android的文档：

You are supplying File wrong parameters. From Android doc:

File(String parent, String child) 
    parent - The parent pathname string
    child - The child pathname string 

在您的code：

parent => \\data  
child => \\data\\com.mypck.myapp\\databases\\database  
resulting path => \\data\\data\\com.mypck.myapp\\databases\\database => wrong

这可能是这样的：

It could be like this:

String sd = Environment.getExternalStorageDirectory();
if (sd.canWrite()) {
    String currentDBPath = "data/data/com.mypck.myapp/databases/your_database_name.db";
    String backupDBPath = sd + "/your_output_file_name.db";
    File currentDB = new File(currentDBPath);
    File backupDB = new File(backupDBPath);
    /* ... */

我很惊讶这个工作在模拟器，我对此表示怀疑。它可能会创建一个空文件，原因至少这行做某种感觉，虽然你的变量是不是你叫他们：

It surprises me this works on emulator, I doubt that. It probably creates an empty file becuase at least this line makes some sort of sense, although your variables are not what you named them:

File backupDB = new File(sd, backupDBPath);

另外，你或许应该创建一个最后块，并做有一些 FileChannel 清理。

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