安卓：SQLite的，cursor.moveToNext（）始终返回false

Question

下面的语句cursor.moveToNext()永远是假的。我期望循环执行一次。我测试过查询实际返回数据。

有谁知道是怎么回事？

String query ="SELECT(SELECT COUNT(*) FROM Table1) as count1, (SELECT COUNT(*) FROM Table2) as count2;"; 

    Cursor mCursor = mDb.rawQuery(query, null); 

    if (mCursor != null) { 
     mCursor.moveToFirst(); 
    } 

    while (cursor.moveToNext()) { //<---------------return false here??? 
     String result_0=cursor.getString(0); 
    } 

Answer 1

我知道你已经解决你的问题，但这里是发生了什么演练：

Cursor mCursor = mDb.rawQuery(query, null); 

// At this point mCursor is positioned at just before the first record. 

if (mCursor != null) { 
    mCursor.moveToFirst(); 
    // mCursor is now pointing at the first (and only) record 
} 

while (mCursor.moveToNext()) { 
    String result_0=cursor.getString(0); 
} 

// The loop above was skipped because `.moveToNext()` caused mCursor 
// to move past the last record. 

所以，在你只需要一个记录的情况下，你只需要要么mCursor.moveToFirst()OR您的mCursor.moveToNext()。

Answer 2

你可以用这种方式迭代游标。

if(moveCursor.moveToFirst()){ 
     do{ 
      //your code 

     }while(moveCursor.moveToNext()); 
    }