我有以下代码来获取实际值的总和(存储在 SQlite DB 中的债务金额:
public double getsumdebt() {
Cursor mCursor = db.rawQuery("SELECT SUM(CurrentAmount) FROM tblDebts", null);
if(mCursor.moveToFirst()) {
return mCursor.getDouble(0);
}
return mCursor.getDouble(0);
}
我正在尝试返回“CurrentAmount”列中所有值的总和并将其显示在文本视图中:
DbAdapter db2 = new DbAdapter(this);
double sum= new Double(db2.getsumdebt());
//sum = db2.getsumdebt();
bar.setText("Progress: "+currencysymbol +current +" / " + currencysymbol + sum);
但是,当我在模拟器中运行应用程序时,在启动期间我会强制关闭,DDMS 日志中有以下内容:
09-26 19:01:19.098: 错误/AndroidRuntime(677): 致命异常: main 09-26 19:01:19.098: 错误/AndroidRuntime(677): java.lang.RuntimeException: 无法启动活动 ComponentInfo{com. evanrich.android.debtdestroyer/com.evanrich.android.debtdestroyer.mainActivity}:java.lang.NullPointerException 09-26 19:01:19.098:错误/AndroidRuntime(677):在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java :2663) 09-26 19:01:19.098: 错误/AndroidRuntime(677): 在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) 09-26 19:01:19.098: 错误/AndroidRuntime(677):在 android.app.ActivityThread.access$2300(ActivityThread.java:125) 09-26 19:01:19.098: 错误/AndroidRuntime(677): 在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 09 -26 19:01:19.098:错误/AndroidRuntime(677):在 android.os.Handler.dispatchMessage(Handler.java:99) 09-26 19:01:19.098: 错误/AndroidRuntime(677): 在 android.os.Looper.loop(Looper.java:123) 09-26 19 :01:19.098: ERROR/AndroidRuntime(677): at android.app.ActivityThread.main(ActivityThread.java:4627) 09-26 19:01:19.098: ERROR/AndroidRuntime(677): at java.lang.reflect。 Method.invokeNative(Native Method) 09-26 19:01:19.098: ERROR/AndroidRuntime(677): at java.lang.reflect.Method.invoke(Method.java:521) 09-26 19:01:19.098: 错误/AndroidRuntime(677): 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 09-26 19:01:19.098: 错误/AndroidRuntime(677): 在 com.android.internal。 os.ZygoteInit.main(ZygoteInit.java:626) 09-26 19:01:19.098: ERROR/AndroidRuntime(677): at dalvik.system.NativeStart.main(Native Method) 09-26 19:01:19.098:错误/AndroidRuntime(677): 由: java.lang.NullPointerException 09-26 19:01:19.098: 错误/AndroidRuntime(677): at com.evanrich.android.debtdestroyer.database.DbAdapter.getsumdebt(DbAdapter.java: 106) 09-26 19:01:19.098: 错误/AndroidRuntime(677): 在 com.evanrich.android.debtdestroyer.mainActivity.onCreate(mainActivity.java:73) 09-26 19:01:19.098: 错误/AndroidRuntime( 677): 在 android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 09-26 19:01:19.098: 错误/AndroidRuntime(677): 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627) 09 -26 19:01:19.098: 错误/AndroidRuntime(677): ... 11 更多getsumdebt(DbAdapter.java:106) 09-26 19:01:19.098: 错误/AndroidRuntime(677): 在 com.evanrich.android.debtdestroyer.mainActivity.onCreate(mainActivity.java:73) 09-26 19:01: 19.098: 错误/AndroidRuntime(677): 在 android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 09-26 19:01:19.098: 错误/AndroidRuntime(677): 在 android.app.ActivityThread.performLaunchActivity(ActivityThread .java:2627) 09-26 19:01:19.098: 错误/AndroidRuntime(677): ... 11 更多getsumdebt(DbAdapter.java:106) 09-26 19:01:19.098: 错误/AndroidRuntime(677): 在 com.evanrich.android.debtdestroyer.mainActivity.onCreate(mainActivity.java:73) 09-26 19:01: 19.098: 错误/AndroidRuntime(677): 在 android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 09-26 19:01:19.098: 错误/AndroidRuntime(677): 在 android.app.ActivityThread.performLaunchActivity(ActivityThread .java:2627) 09-26 19:01:19.098: 错误/AndroidRuntime(677): ... 11 更多ActivityThread.performLaunchActivity(ActivityThread.java:2627) 09-26 19:01:19.098: ERROR/AndroidRuntime(677): ... 11 更多ActivityThread.performLaunchActivity(ActivityThread.java:2627) 09-26 19:01:19.098: ERROR/AndroidRuntime(677): ... 11 更多
看起来它无法对存储在数据库中的实际值求和。谁能帮我?
仅供参考,这是我的表构造函数:
private static final String DATABASE_CREATE =
"CREATE TABLE IF NOT EXISTS tblDebts (_id integer primary key autoincrement, "
+ "Debt text not null, StartingAmount real, CurrentAmount real, "
+ "InterestRate real, DueDate integer, MinimumPayment real );";
谢谢。