从SQLite数据库android访问数据后，应用程序崩溃

问题描述

在我的代码中，我正在创建一个sqlite数据库和一个表，并将数据添加到表中，这部分工作正常。但是，当我访问数据时会出现问题。它检索存储的数据，最后使应用程序崩溃。 while循环会导致这种情况吗？

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();
        }

    }
} 

以下是日志：

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)

解决方法

在游标的各行之间循环的方式是错误的。
删除对c.moveToFirst();的第一个调用，然后使用c.moveToNext()来检查游标中是否还有另一行：

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之后停止，因为c.moveToNext()将返回false。