java - 嵌套的 Do-While 循环通过游标进行索引 - 不起作用

Question

这应该有效吗？

Cursor c1 = db.m1();
Cursor c2 = db.m2();

do{

    do{
        String foodDate = c1.getString(1);
        String foodTime = c1.getString(2);

        String sympDate = c2.getString(1);
        String sympTime = c2.getString(2);
        // more stuff
    }while(c1.moveToNext());

}while(c2.moveToNext());    

如果我删除其中一个 do while 循环，它就可以正常工作，每个单独的循环都会毫无问题地遍历每个光标条目。

但是在两个循环都完好无损的情况下，我不断收到以下错误:

03-19 13:09:05.751: W/dalvikvm(3616): threadid=1: thread exiting with uncaught exception (group=0xb3a54b90)
03-19 13:09:05.761: E/AndroidRuntime(3616): FATAL EXCEPTION: main
03-19 13:09:05.761: E/AndroidRuntime(3616): java.lang.IllegalStateException: Could not execute method of the activity
03-19 13:09:05.761: E/AndroidRuntime(3616):     at android.view.View$1.onClick(View.java:3814)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at android.view.View.performClick(View.java:4424)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at android.view.View$PerformClick.run(View.java:18383)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at android.os.Handler.handleCallback(Handler.java:733)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at android.os.Handler.dispatchMessage(Handler.java:95)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at android.os.Looper.loop(Looper.java:137)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at android.app.ActivityThread.main(ActivityThread.java:4998)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at java.lang.reflect.Method.invokeNative(Native Method)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at java.lang.reflect.Method.invoke(Method.java:515)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at dalvik.system.NativeStart.main(Native Method)
03-19 13:09:05.761: E/AndroidRuntime(3616): Caused by: java.lang.reflect.InvocationTargetException
03-19 13:09:05.761: E/AndroidRuntime(3616):     at java.lang.reflect.Method.invokeNative(Native Method)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at java.lang.reflect.Method.invoke(Method.java:515)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at android.view.View$1.onClick(View.java:3809)
03-19 13:09:05.761: E/AndroidRuntime(3616):     ... 11 more
03-19 13:09:05.761: E/AndroidRuntime(3616): Caused by: android.database.CursorIndexOutOfBoundsException: Index 210 requested, with a size of 210
03-19 13:09:05.761: E/AndroidRuntime(3616):     at android.database.AbstractCursor.checkPosition(AbstractCursor.java:426)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:136)
03-19 13:09:05.761: E/AndroidRuntime(3616):     at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:50)

Answer 1

一旦内部循环完成，光标就位于其末尾，因此当外部循环导致内部循环再次运行时，它会尝试移动到下一个项目(该项目不存在)。您需要告诉第一个光标重置到其初始位置。

c1.moveToFirst();

在内循环正上方的外循环内部。