如何在 for 循环或 while 循环中引用光标项？

Question

我正在尝试循环创建选项卡的数据库值。我设置了一个名为 createTab 的方法，它接受 Long 值和 String 值。它正在处理静态数据，但我很难理解如何循环 SQLite 数据库记录。

这是我失败的尝试（用小于符号替换 [小于]）：

for (int i = 0; i [lessthan] mCursor.getCount(); i++)
{
 createTab(
  mCursor.getLong(mCursor.getColumnIndexOrThrow("_id")),
  mCursor.getString(mCursor.getColumnIndexOrThrow("category")));
}

您可能不需要 LogCat 来知道我在上面的代码中做错了什么，但以防万一...

08-27 21:28:18.268: ERROR/AndroidRuntime(232): Caused by: android.database.CursorIndexOutOfBoundsException: Index -1 requested, with a size of 3
08-27 21:28:18.268: ERROR/AndroidRuntime(232):     at android.database.AbstractCursor.checkPosition(AbstractCursor.java:580)
08-27 21:28:18.268: ERROR/AndroidRuntime(232):     at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:172)
08-27 21:28:18.268: ERROR/AndroidRuntime(232):     at android.database.AbstractWindowedCursor.getLong(AbstractWindowedCursor.java:99)
08-27 21:28:18.268: ERROR/AndroidRuntime(232):     at com.toBuy.Main.createTabs(Main.java:51)
08-27 21:28:18.268: ERROR/AndroidRuntime(232):     at com.toBuy.Main.onCreate(Main.java:38)
08-27 21:28:18.268: ERROR/AndroidRuntime(232):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
08-27 21:28:18.268: ERROR/AndroidRuntime(232):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
08-27 21:28:18.268: ERROR/AndroidRuntime(232):     ... 11 more
08-27 21:28:18.278: INFO/Process(54): Sending signal. PID: 232 SIG: 3
08-27 21:28:18.278: INFO/dalvikvm(232): threadid=7: reacting to signal 3
08-27 21:28:18.338: INFO/dalvikvm(232): Wrote stack trace to '/data/anr/traces.txt'
08-27 21:28:18.508: INFO/ARMAssembler(54): generated scanline__00000077:03515104_00000000_00000000 [ 27 ipp] (41 ins) at [0x285a68:0x285b0c] in 713498 ns
08-27 21:28:18.518: INFO/ARMAssembler(54): generated scanline__00000077:03515104_00001001_00000000 [ 64 ipp] (84 ins) at [0x285b10:0x285c60] in 1897448 ns
08-27 21:28:28.086: WARN/ActivityManager(54): Launch timeout has expired, giving up wake lock!
08-27 21:28:28.097: WARN/ActivityManager(54): Activity idle timeout for HistoryRecord{4390bf70 com.toBuy/.Main}

谢谢您的帮助。

Answer 1

您需要先定位光标，然后才能调用 getLong 或 getString。发出查询后，Cursor 位于第一行之前，因此您应该在循环中调用 moveToNext。像这样的东西：

int size = mCursor.getCount();
for (int i = 0; i < size; i++) {

    // Position the cursor
    mCursor.moveToNext();

    // Fetch your data values
    long id = mCursor.getLong(mCursor.getColumnIndex("_id"));
    String cat = mCursor.getString(mCursor.getColumnIndex("category"));
}

Answer 2

在我的代码中，我从 SQLite 数据库获取值，并使用 Cursor 将该值存储在模型类（FriendData 是我的模型类）的对象数组中。

   Cursor cursor = friendAdapter.fetchData(); //call method for fetch data from databse and fetched data is stored into cursor
    int cursorSize = cursor.getCount();

    if (cursor != null && cursor.moveToFirst()) {
         FriendData[] friendData=new FriendData[cursorSize];  //create array of objects as size of cursor

            for (int i = 0; i < cursorSize; i++) {
                   friendData[i]=new FriendData();

                  /*store fetched data in some variables. In my code I have store value of cursor in friendName String variable*/
                  friendName = cursor.getString(cursor.getColumnIndex(FriendAdapter.FRIEND_NM));

                 /* set friendName variable value in array of object*/
                 friendData[i].setFriendName(friendName);

              cursor.moveToNext();  //move cursor for pointing to next fetched record
           }
     }

首先，我检查光标的条件是否为空，然后移动光标对象以指向获取的第一条记录。然后我使用 getCount() 方法计算光标的大小。之后，使用 for 循环将所有数据存储在对象数组中，最后光标指向要获取的下一条记录。

Answer 3

使用以下 for 循环：

   for(mCursor.moveToFirst();!mCursor.isAfterLast();mCursor.moveToNext()){
        createTab(
  mCursor.getLong(mCursor.getColumnIndexOrThrow("_id")),
  mCursor.getString(mCursor.getColumnIndexOrThrow("category")));    
        }

虽然，while 循环会简单得多：

while (mCursor.moveToNext()) { createTab(
  mCursor.getLong(mCursor.getColumnIndexOrThrow("_id")),
  mCursor.getString(mCursor.getColumnIndexOrThrow("category")));    

}

在这两种情况下，您都不需要手动设置光标的起始位置。