从 SQLite 数据库访问数据后应用程序崩溃 android

Question

在我的代码中，我正在创建一个 SQLite 数据库和一个 table，并将数据添加到 table，这部分工作正常。但是当我访问数据时，问题就出现了。它检索存储的数据并在最后使应用程序崩溃。 while循环会导致这个吗？

这是我的代码：

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //creating  a new Or accessing an existing database
        SQLiteDatabase myDatabase = this.openOrCreateDatabase("Users",MODE_PRIVATE,null);

        //creating a table if it does not exist
        myDatabase.execSQL("CREATE TABLE IF NOT EXISTS users(name VARCHAR,age INT(3))");

        //inserting data into the users table
        //single row of values
        myDatabase.execSQL("INSERT INTO users(name,age) VALUES('Robert',28)");
        //multiple rows of values
        myDatabase.execSQL("INSERT INTO users(name,age) VALUES('Derek',30), ('Israel',31), ('Jared',24)");

        //accessing data and traversing across table users
        Cursor c = myDatabase.rawQuery("SELECT * FROM users",null);

        int nameIndex = c.getColumnIndex("name");   //setting index  for name column
        int ageIndex = c.getColumnIndex("age");     //setting index  for age column

        c.moveToFirst(); //setting the cursor on starting position

//traversing across the table row by row
        while (c != null){
            Log.i("name",c.getString(nameIndex));
            Log.i("age",c.getString(ageIndex));

            c.moveToNext();
        }

    }
}

这是日志：

2020-10-26 13:29:53.199 18545-18545/com.example.databasedemo1 I/name: Robert
2020-10-26 13:29:53.199 18545-18545/com.example.databasedemo1 I/age: 28
2020-10-26 13:29:53.199 18545-18545/com.example.databasedemo1 I/name: Derek
2020-10-26 13:29:53.199 18545-18545/com.example.databasedemo1 I/age: 30
2020-10-26 13:29:53.199 18545-18545/com.example.databasedemo1 I/name: Israel
2020-10-26 13:29:53.199 18545-18545/com.example.databasedemo1 I/age: 31
2020-10-26 13:29:53.199 18545-18545/com.example.databasedemo1 I/name: Jared
2020-10-26 13:29:53.199 18545-18545/com.example.databasedemo1 I/age: 24
2020-10-26 13:29:53.200 18545-18545/com.example.databasedemo1 D/AndroidRuntime: Shutting down VM
2020-10-26 13:29:53.206 18545-18545/com.example.databasedemo1 E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.databasedemo1, PID: 18545
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.databasedemo1/com.example.databasedemo1.MainActivity}: 

android.database.CursorIndexOutOfBoundsException: Index 4 requested, with a size of 4
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6541)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
     Caused by: android.database.CursorIndexOutOfBoundsException: Index 4 requested, with a size of 4
        at android.database.AbstractCursor.checkPosition(AbstractCursor.java:460)
        at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:136)
        at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:50)
        at com.example.databasedemo1.MainActivity.onCreate(MainActivity.java:39)
        at android.app.Activity.performCreate(Activity.java:6975)

Answer 1

您循环游标行的方式是错误的。
删除对 c.moveToFirst(); 的第一次调用并使用 c.moveToNext() 检查 Cursor 中是否还有另一行：

while (c.moveToNext()) {
    Log.i("name",c.getString(nameIndex));
    Log.i("age",c.getString(ageIndex));
}

这样循环将在访问最后一行后停止，因为 c.moveToNext() 将 return false.

从 SQLite 数据库访问数据后应用程序崩溃 android

App crashes after accessing data from SQLite Database android

java

database

sqlite

android

android-sqlite