尝试插入SQLite时出现NullPointerException-Android
作者：互联网
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: main
01-03 17:09:18.232: E/AndroidRuntime(1712): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.Highscores}: java.lang.NullPointerException
01-03 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.access$600(ActivityThread.java:141)
01-03 17:09:18.232: E/AndroidRuntime(1712): at android.app.ActivityThread$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.NullPointerException
01-03 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).
标签：insertion,android,java,sqlite,nullpointerexception 来源： https://codeday.me/bug/20191012/1903880.html