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android - file.createNewFile() 的结果；将 SQLite 数据库导出到 CSV Android Java 时被忽略

问题描述

我正在尝试使用 ExportDatabaseCSVTask 将我的 SQLite 数据库导出为 CSV。

经过几次更正后，它是这样的：

在 CatalogActivity 中单击按钮：

@Override
    public boolean onOptionsItemSelected(MenuItem item) {
        //export data to CSV using method in InventoryProvider via separate java class ExportDatabaseCSVTask
            case  R.id.export_to_csv:
                tryExporting();
              return true;
        }
        return super.onOptionsItemSelected(item);
    }


    public void tryExporting() {
        if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.READ_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, 1);
            return;
        }
        new ExportDatabaseCSVTask(this).execute();
    }


    @Override
    public void onRequestPermissionsResult(int requestCode,
                                           @NonNull String permissions[], @NonNull int[] grantResults) {
        switch (requestCode) {
            case REQUEST_READ_EXTERNAL_STORAGE: {
                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    new ExportDatabaseCSVTask(this).execute();
                }
            }
        }

这是被触发的类

            public class ExportDatabaseCSVTask extends AsyncTask<String, String, Boolean> {
        SQLiteDatabase database;
        private Context context;
        private ProgressDialog dialog;
        InventoryProvider iProvider;
        InventoryDbHelper mDbHelper;

        public ExportDatabaseCSVTask(Context context) {
            this.context = context;
        }

        @Override
        protected void onPreExecute() {

            if (dialog == null) {
                dialog = new ProgressDialog(context);
                dialog.setMessage("Downloading Files... Please Wait...");
                dialog.show();
            }

        }



        @TargetApi(Build.VERSION_CODES.O)
        protected Boolean doInBackground(final String... args) {
            File exportDir = new File(Environment.getExternalStorageDirectory(), "/codesss/");

        if (!exportDir.exists()) { exportDir.mkdirs();
            if(!exportDir.mkdirs()) {
                Log.e("mDebug", "Couldn't get the directory"); 
            }
        }
                File file = new File(exportDir, "inventory.csv");
                try {
                    file.createNewFile();
                    if(!file.createNewFile()) {
                        Log.e("mDebug", "Couldn't create the file"); --> ERROR HERE result is ignored error
                    }


CSVWriter csvWrite = new CSVWriter(new FileWriter(file));
                    database = this.mDbHelper.getWritableDatabase();
                    database = this.mDbHelper.getReadableDatabase();
                    Cursor curCSV = database.rawQuery("SELECT * FROM inventory", null);


                    csvWrite.writeNext(curCSV.getColumnNames());
                    while (curCSV.moveToNext()) {
                        String arrStr[] = null;
                        String[] mySecondStringArray = new String[curCSV.getColumnNames().length];
                        for (int i = 0; i < curCSV.getColumnNames().length; i++) {
                            mySecondStringArray[i] = curCSV.getString(i);
                        }
                        csvWrite.writeNext(mySecondStringArray);
                    }

                    csvWrite.close();
                    curCSV.close();
                    return true;
                } catch (IOException e) {
                    return false;
                }
            }



        protected void onPostExecute(final Boolean success) {
            if (dialog != null) {
                if (dialog.isShowing()) { dialog.dismiss();
                 dialog = null;
                }
            }
          // if ((dialog != null)) { this.dialog.dismiss(); }
           if (success) {
               Toast.makeText(context, "Export successful!", Toast.LENGTH_SHORT).show();
     ShareFile();
            } else {
                Toast.makeText(context, "Export failed", Toast.LENGTH_SHORT).show();
           }
        }

     private void ShareFile() {
            File exportDir = new File(Environment.getExternalStorageDirectory(), "/codesss/");
            String fileName = "inventory.csv";
            File sharingGifFile = new File(exportDir, fileName);
            Intent shareIntent = new Intent(android.content.Intent.ACTION_SEND);
            shareIntent.setType("application/csv");
            Uri uri = Uri.fromFile(sharingGifFile);
            shareIntent.putExtra(Intent.EXTRA_STREAM, uri);
            context.startActivity(Intent.createChooser(shareIntent, "Share CSV"));
        }
    }

已添加权限

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

更新

所以，现在错误在于创建文件。file.createNewFile() 的结果；被忽略

调试显示文件夹已创建 - D/myAppName: 文件夹存在：/storage/emulated/0/codess但是，它是空的，不存在文件夹。

为这个新问题创建了单独的问题 - Exporting SQLite Database to csv file in android

标签： androidsqliteexport-to-csv

解决方案

对此onPreExecute()进行更改：

if (dialog == null) {
    dialog = new ProgressDialog(context);
    dialog.setMessage("Downloading Files... Please Wait...");
}

这样您就不会每次都创建新的对话框。
再次onPostExecute()检查null：

if (dialog != null) {
    if (dialog.isShowing()) { 
        dialog.dismiss(); 
        dialog = null;
    }
}

此外，由于此对话框 ID 是使用上下文创建的，因此请CatalogActivity确保在显示对话框时此活动未关闭。
也改变所有：

Toast.makeText(CatalogActivity.getApplicationContext...

和

Toast.makeText(context....

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