尝试插入SQLite时出现NullPointerException-Android

概述遵循Android标签的任何人都可能对我很熟悉.我很难为自己的高分实现SQLite数据库.这也是我第一次使用SQLite.我正在尝试仅插入两个变量-int和long.我的insert()方法无法正常工作.除了上面讨论的内容外,任何其他建议也应受到赞赏.预先感谢您的帮助.Highscores.javapublicclass

遵循Android标签的任何人都可能对我很熟悉.我很难为自己的高分实现sqlite数据库.这也是我第一次使用sqlite.

我正在尝试仅插入两个变量-int和long.我的insert()方法无法正常工作.除了上面讨论的内容外,任何其他建议也应受到赞赏.

预先感谢您的帮助.

Highscores.java

public class Highscores extends Activity {    DatabaseHelper dh;    sqliteDatabase db;    @OverrIDe    public voID onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentVIEw(R.layout.highscoresmain);        dh = new DatabaseHelper(this);        dh.openDB(db);        long x = 11;        int y = 22;        TextVIEw rank = (TextVIEw)findVIEwByID(R.ID.rank);        TextVIEw percentage = (TextVIEw)findVIEwByID(R.ID.percentage);        TextVIEw score = (TextVIEw)findVIEwByID(R.ID.score);        TextVIEw r1r = (TextVIEw)findVIEwByID(R.ID.r1r);        TextVIEw r1p = (TextVIEw)findVIEwByID(R.ID.r1p);        TextVIEw r1s = (TextVIEw)findVIEwByID(R.ID.r1s);        dh.insert(x, y, db);  //line 55        scores = dh.getscore(db);        percentages = dh.getPercentage(db);        rank.setText("Rank Column - TEST");        percentage.setText("Percentage Column - TEST ");        score.setText("score Column - Test");        r1r.setText("test..rank");        r1p.setText("" + percentages);        r1s.setText("test..score");        table = (tableLayout)findVIEwByID(R.ID.tableLayout);        dh.closeDB(db);    }}

DatabaseHelper.java

public class DatabaseHelper extends sqliteOpenHelper {     sqliteDatabase db;    // table columns names.     private static final String RANK = "_ID";     private static final String score = "score";     private static final String PERCENTAGE = "percentage";    public DatabaseHelper(Context context) {         super(context, DB_name, null, DATABASE_VERSION);     }    public sqliteDatabase openDB(sqliteDatabase db) {        db = this.getWritableDatabase();        return db;    }    public int getPercentage(sqliteDatabase db) {        //Cursor c = db.rawquery("SELECT " + PERCENTAGE + " FROM " + table + " WHERE " + PERCENTAGE + " = " + 22 + ";", null);        Cursor c = db.rawquery("SELECT " + PERCENTAGE + " FROM " + table + ";", null);        int i = 0;        if(c.getCount() == 0) {            i = 333;        } else if (c.getCount() == 1) {            i = 444;        } else {            i = 888;               /*c.movetoFirst();               int columnIndex = c.getInt(c.getColumnIndex("PERCENTAGE"));               if(columnIndex != -1) {                   i = c.getInt(columnIndex);               } else {                    i = 999;                }*/        }        c.close();        return i;   }    //Insert new record.    public long insert(long score, int percentage, sqliteDatabase db) {        ContentValues values = new ContentValues();        values.put(score, score);        values.put(PERCENTAGE, percentage);        return db.insert(table, null, values);  //line 120    }    public synchronized voID closeDB(sqliteDatabase db) {        if(db != null) {            db.close();        }        super.close();    }    public voID onCreate(sqliteDatabase db) {        db.execsql("CREATE table " + table + " ("                + RANK + " INTEGER PRIMARY KEY autoINCREMENT,"                + score + " LONG,"                + PERCENTAGE + " INTEGER"                + ");");}

LogCat输出

01-03 17:09:18.232: E/AndroIDRuntime(1712): FATAL EXCEPTION: main01-03 17:09:18.232: E/AndroIDRuntime(1712): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.Highscores}: java.lang.NullPointerException01-03 17:09:18.232: E/AndroIDRuntime(1712):     at androID.app.ActivityThread.performlaunchActivity(ActivityThread.java:2180)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at androID.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at androID.app.ActivityThread.access0(ActivityThread.java:141)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at androID.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at androID.os.Handler.dispatchMessage(Handler.java:99)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at androID.os.Looper.loop(Looper.java:137)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at androID.app.ActivityThread.main(ActivityThread.java:5039)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at java.lang.reflect.Method.invokeNative(Native Method)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at java.lang.reflect.Method.invoke(Method.java:511)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at com.androID.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at com.androID.internal.os.ZygoteInit.main(ZygoteInit.java:560)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at dalvik.system.NativeStart.main(Native Method)01-03 17:09:18.232: E/AndroIDRuntime(1712): Caused by: java.lang.NullPointerException01-03 17:09:18.232: E/AndroIDRuntime(1712):     at com.example.test.DatabaseHelper.insert(DatabaseHelper.java:120)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at com.example.test.Highscores.onCreate(Highscores.java:55)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at androID.app.Activity.performCreate(Activity.java:5104)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at androID.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)01-03 17:09:18.232: E/AndroIDRuntime(1712):     at androID.app.ActivityThread.performlaunchActivity(ActivityThread.java:2144)01-03 17:09:18.232: E/AndroIDRuntime(1712):     ... 11 more

解决方法:

在这行上,打开数据库：

dh.openDB(db);

这会将数据库的成员变量存储在DatabaseHelper.db中(但没有其他地方,尤其是在Highscores.db中).然后,您致电：

dh.insert(x, y, db);

使用Highscores中的空db对象.最后,在insert()中,使用此空db对象：

return db.insert(table, null, values);

相反,您应该使用以下代码作为insert()方法：

public long insert(long score, int percentage) { // Remove db parameter    ContentValues values = new ContentValues();    values.put(score, score);    values.put(PERCENTAGE, percentage);    return db.insert(table, null, values); // This will use the member variable}

然后,调用dh.insert(x,y);代替.

您还应该将openDB(sqliteDatabase db)更改为openDB(),以便它可以写入正确的数据库.就目前而言,它只会覆盖局部变量的值(一旦函数作用域完成,它就不会改变).

总结

以上是内存溢出为你收集整理的尝试插入SQLite时出现NullPointerException-Android全部内容，希望文章能够帮你解决尝试插入SQLite时出现NullPointerException-Android所遇到的程序开发问题。

如果觉得内存溢出网站内容还不错，欢迎将内存溢出网站推荐给程序员好友。