本文介绍了游标RawQuery上的NullPointerException-Android的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我试图创建一个数据库，插入数据库，从数据库中拉出，然后将内容（长）显示到TextView中。
I am trying to create a db, insert into the db, pull from the db and display the contents (long) to a TextView.
我想我是创建并正确插入数据库。在我的 getScore（）方法中，我得到了NullPointerException。
I think I am creating and inserting into the db correctly. In my getScore() method I am getting a NullPointerException.
对代码结构的任何帮助也深表感谢！
Any help on code structure is much appreciated as well! Thank you in advance.
DatabaseHelper.java
DatabaseHelper.java
public class DatabaseHelper extends SQLiteOpenHelper {
SQLiteDatabase db;
// Table columns names.
private static final String SCORE = "score";
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, DATABASE_VERSION);
}
public SQLiteDatabase openDB() {
db = this.getWritableDatabase();
return db;
}
public long getScore(SQLiteDatabase db) {
//Cursor c = db.rawQuery("SELECT " + SCORE + " FROM " + TABLE + " WHERE " + SCORE + " = " + 11 + ";", null); //Line 45
Cursor c = db.rawQuery("SELECT " + SCORE + " FROM " + TABLE + ";", null); //Line 39
long 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("SCORE"));
if(columnIndex != -1) {
i = c.getLong(columnIndex);
} else {
i = 999;
}*/
}
c.close();
return i;
}
//Insert new record.
public long insert(long score, int percentage) {
ContentValues values = new ContentValues();
values.put(SCORE, score);
values.put(PERCENTAGE, percentage);
return db.insert(TABLE, null, values);
}
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"
+ ");");
}
}
Highscores.java
Highscores.java
public class Highscores extends Activity {
DatabaseHelper dh;
SQLiteDatabase db;
long scores;
TextView score;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.highscoresmain);
dh = new DatabaseHelper(this);
dh.openDB();
long x = 11;
int y = 22;
TextView score = (TextView)findViewById(R.id.score);
TextView r1s = (TextView)findViewById(R.id.r1s);
dh.insert(x, y);
scores = dh.getScore(db); //Line 56
score.setText("Score Column - TEST");
r1s.setText("" + score);
dh.closeDB(db);
}
}
LogCat输出
01-03 17:36:01.172: E/AndroidRuntime(1941): FATAL EXCEPTION: main
01-03 17:36:01.172: E/AndroidRuntime(1941): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.Highscores}: java.lang.NullPointerException
01-03 17:36:01.172: E/AndroidRuntime(1941): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
01-03 17:36:01.172: E/AndroidRuntime(1941): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
01-03 17:36:01.172: E/AndroidRuntime(1941): at android.app.ActivityThread.access$600(ActivityThread.java:141)
01-03 17:36:01.172: E/AndroidRuntime(1941): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
01-03 17:36:01.172: E/AndroidRuntime(1941): at android.os.Handler.dispatchMessage(Handler.java:99)
01-03 17:36:01.172: E/AndroidRuntime(1941): at android.os.Looper.loop(Looper.java:137)
01-03 17:36:01.172: E/AndroidRuntime(1941): at android.app.ActivityThread.main(ActivityThread.java:5039)
01-03 17:36:01.172: E/AndroidRuntime(1941): at java.lang.reflect.Method.invokeNative(Native Method)
01-03 17:36:01.172: E/AndroidRuntime(1941): at java.lang.reflect.Method.invoke(Method.java:511)
01-03 17:36:01.172: E/AndroidRuntime(1941): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
01-03 17:36:01.172: E/AndroidRuntime(1941): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
01-03 17:36:01.172: E/AndroidRuntime(1941): at dalvik.system.NativeStart.main(Native Method)
01-03 17:36:01.172: E/AndroidRuntime(1941): Caused by: java.lang.NullPointerException
01-03 17:36:01.172: E/AndroidRuntime(1941): at com.example.test.DatabaseHelper.getScore(DatabaseHelper.java:39)
01-03 17:36:01.172: E/AndroidRuntime(1941): at com.example.test.Highscores.onCreate(Highscores.java:56)
01-03 17:36:01.172: E/AndroidRuntime(1941): at android.app.Activity.performCreate(Activity.java:5104)
01-03 17:36:01.172: E/AndroidRuntime(1941): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
01-03 17:36:01.172: E/AndroidRuntime(1941): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
01-03 17:36:01.172: E/AndroidRuntime(1941): ... 11 more
编辑：新的 getScore（）方法。
public long getScore() {
Cursor c = db.rawQuery("SELECT " + SCORE + " FROM " + TABLE + " WHERE " + SCORE + " = " + 11 + ";", null);
//Cursor c = db.rawQuery("SELECT " + SCORE + " FROM " + TABLE + ";", null);
long i = 0;
if(c.getCount() == 0) {
i = 333;
} else if (c.getCount() == 1) {
i = 444;
} else if (c.getCount() == 2) {
i = 555;
} else {
i = 666;
/*c.moveToFirst();
int columnIndex = c.getInt(c.getColumnIndex("SCORE"));
if(columnIndex != -1) {
i = c.getLong(columnIndex);
} else {
i = 999;
}*/
}
c.close();
return i;
}
这仍会返回i，其值为666。
This still returns i with a value of 666.
推荐答案
您在这里覆盖本地的 db 值： public long getScore（SQLiteDatabase db）{... 。删除该参数，它应该可以工作。
You're overriding your local db value here: public long getScore(SQLiteDatabase db) { ... . Remove that parameter and it should work.
这篇关于游标RawQuery上的NullPointerException-Android的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！