beginTransaction（）空指针？

Question

所以我的代码部分出了问题，我的sdcard将.csv文件导入到我的应用程序的sqlite数据库中。根据我的LogCat我的“db.beginTransaction（）;”由于空指针线是否失败？我真的不知道如何解决这个问题，我希望有人能够帮助我！

以下是将csv文件导入数据库的代码：

@Override
    public void onStart(){
        super.onStart();


        FileReader fr;
        try {
            fr = new FileReader(new File("mnt/sdcard/database/",
                    "fcmtest.csv"));
        } catch (FileNotFoundException e) {
            throw new Error("ERROR File Not Found");
        }
        BufferedReader br = new BufferedReader(fr);
        String data = "";
        String tableName ="MY_TABLE";
        String columns = "Serial Numbers,PartNumber,Result,Date,Time,Operator";
        String InsertString1 = "INSERT INTO " + tableName + " (" + columns + ") values(";
        String InsertString2 = ");";

        db.beginTransaction();
        try {
            while ((data = br.readLine()) != null) {
                StringBuilder sb = new StringBuilder(InsertString1);
                String[] sarray = data.split(",");
                sb.append("'" + sarray[0] + "',");
                sb.append(sarray[1] + "',");
                sb.append(sarray[2] + "',");
                sb.append(sarray[3] + "',");
                sb.append(sarray[4] + "',");
                sb.append(sarray[5] + "'");
                sb.append(InsertString2);
                db.execSQL(sb.toString());
            }
        } catch (SQLException e) {
            throw new Error("Error copying database");
        } catch (IOException e) {
            throw new Error("Error IOException");
        }
        db.setTransactionSuccessful();
        db.endTransaction();

    }

这是Logcat：

02-01 14:20:04.071: W/dalvikvm(7655): threadid=1: thread exiting with uncaught exception (group=0x41033930)
02-01 14:20:04.071: E/AndroidRuntime(7655): FATAL EXCEPTION: main
02-01 14:20:04.071: E/AndroidRuntime(7655): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.magna.magna/com.magna.magna.FCM}: java.lang.NullPointerException
02-01 14:20:04.071: E/AndroidRuntime(7655):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at android.os.Handler.dispatchMessage(Handler.java:99)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at android.os.Looper.loop(Looper.java:137)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at android.app.ActivityThread.main(ActivityThread.java:5039)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at java.lang.reflect.Method.invokeNative(Native Method)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at java.lang.reflect.Method.invoke(Method.java:511)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at dalvik.system.NativeStart.main(Native Method)
02-01 14:20:04.071: E/AndroidRuntime(7655): Caused by: java.lang.NullPointerException
02-01 14:20:04.071: E/AndroidRuntime(7655):     at com.magna.magna.FCM.onStart(FCM.java:56)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1164)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at android.app.Activity.performStart(Activity.java:5114)
02-01 14:20:04.071: E/AndroidRuntime(7655):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2153)
02-01 14:20:04.071: E/AndroidRuntime(7655):     ... 11 more

at line（FCM.java:56）是db.beginTransaction（）; 提前谢谢！

Answer 1

由于NullPointerException为db，您在该行上获得了null。您永远不会在上面显示的代码中初始化db。您可以通过为null分配非db值来解决此问题。