Question

如果id是他们的表，我想获取行的id。但是在行Cursor cursorc = sqdb.rawQuery（strQue，null）;之后运行应用程序获取空指针异常。有人可以帮我解决这个问题。

这是log cat。

10-13 16:34:22.340: E/AndroidRuntime(914): FATAL EXCEPTION: main
10-13 16:34:22.340: E/AndroidRuntime(914): java.lang.NullPointerException
10-13 16:34:22.340: E/AndroidRuntime(914):  at com.explistview.Test_Demo.previousQuestionCalled(Test_Demo.java:254)
10-13 16:34:22.340: E/AndroidRuntime(914):  at com.explistview.Test_Demo$1.onClick(Test_Demo.java:102)
10-13 16:34:22.340: E/AndroidRuntime(914):  at android.view.View.performClick(View.java:2485)
10-13 16:34:22.340: E/AndroidRuntime(914):  at android.view.View$PerformClick.run(View.java:9080)
10-13 16:34:22.340: E/AndroidRuntime(914):  at android.os.Handler.handleCallback(Handler.java:587)
10-13 16:34:22.340: E/AndroidRuntime(914):  at android.os.Handler.dispatchMessage(Handler.java:92)
10-13 16:34:22.340: E/AndroidRuntime(914):  at android.os.Looper.loop(Looper.java:123)
10-13 16:34:22.340: E/AndroidRuntime(914):  at android.app.ActivityThread.main(ActivityThread.java:3683)
10-13 16:34:22.340: E/AndroidRuntime(914):  at java.lang.reflect.Method.invokeNative(Native Method)
10-13 16:34:22.340: E/AndroidRuntime(914):  at java.lang.reflect.Method.invoke(Method.java:507)
10-13 16:34:22.340: E/AndroidRuntime(914):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
10-13 16:34:22.340: E/AndroidRuntime(914):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
10-13 16:34:22.340: E/AndroidRuntime(914):  at dalvik.system.NativeStart.main(Native Method)

这是活动代码。

 button_Previouse.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    previousQuestionCalled(v);
                }
            });


            button_Next.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub

                    nextQuestionCalled(v);
                }
            });

public void previousQuestionCalled(View view)
    {

        if (StaticClass.QuestionNumber > 0)
        {
            if (!StaticClass.isTest)
            {
                StaticClass.QuestionNumber = -1 + StaticClass.QuestionNumber;
                reHitting2();

                for(i=1 ; i <= vector_Size; i++)
                {
                    String strQue = "select count(question_id) from question_answers where question_id =" + 'i';
                    System.out.println(" i = " + i);

                    Cursor cursorc = sqdb.rawQuery(strQue, null);


                    if (cursorc.moveToFirst())
                    { 
                          int str_id = cursorc.getInt(cursorc.getColumnIndex("question_id"));
                          System.out.println("str_id = " + str_id);
                    }
                }

                if(i > 0)
                {
                    String strUpdateQuery = "";
                }
            }
        }
    }

Answer 1

在行Cursor cursorc = sqdb.rawQuery（strQue，null）;获取空指针异常。

您尚未初始化sqdb变量。

假设您正在使用SQLiteOpenHelper，请在帮助程序上调用getReadbaleDatabase()或getWritableDatabase()以获取SQLiteDatabase引用，您可以将其分配给sqdb变量

我在E / CursorWindow（512）的log cat上有一行错误：字段槽0的错误请求，-1。 numRows = 1，numColumns = 1

列索引无效。变化

cursorc.getColumnIndex("question_id")

到例如。

检索游标中的第一列。您的getColumnIndex("question_id")会返回-1，因为count(question_id)与question_id不同。

Answer 2

更改代码

String strQue = "select count(question_id) from question_answers where question_id =" + 'i';

到

String strQue = "select count(question_id) from question_answers where question_id =" + i;

如果您的列question_id是整数类型

，否则

String strQue = "select count(question_id) from question_answers where question_id =" + "'i'";

Nullpointer异常在Android中

2 个答案: