Question

我试图从表中加载一个值列表，但是光标找不到列？错误的代码：

public final AccessToken[] fetchAccessTokenByServerId(final long serverId) {
    final Cursor c = db.query(
            ACCESS_TOKEN_TABLE,
            new String[] { ACCESS_TOKEN_COL_ID, ACCESS_TOKEN_COL_VALUE },
            ACCESS_TOKEN_COL_SERVER_ID + "=?",
            new String[] { Long.toString(serverId) },
            null,
            null,
            null);

    AccessToken[] result = new AccessToken[c.getCount()];
    for (int i = 0; i < result.length; i++) {
        long id = c.getLong(c.getColumnIndexOrThrow(ACCESS_TOKEN_COL_ID));
        String value = c.getString(c.getColumnIndexOrThrow(ACCESS_TOKEN_COL_VALUE));

        result[i] = new AccessToken(value, id, serverId);
        c.moveToNext();
    }
    return result;
}

public static final String COL_ID = "_id";
public static final String ACCESS_TOKEN_TABLE = "accesstoken";
public static final String ACCESS_TOKEN_COL_ID = COL_ID;
public static final String ACCESS_TOKEN_COL_SERVER_ID = "server_id";
public static final String ACCESS_TOKEN_COL_VALUE = "value";

但是for循环中的前两个语句失败了：

请求索引-1，大小为 1

该表存在以下列：_id（= int），server_id（= int）和value（= string）

有一个条目：1,1，测试

该功能的参数为1.

此致 xZise

Answer 1

在初始化光标后，执行以下操作：

c.moveToFirst();

Answer 2

在这部分代码中我推荐这种方式

原件：

AccessToken[] result = new AccessToken[c.getCount()];
for (int i = 0; i < result.length; i++) {
    long id = c.getLong(c.getColumnIndexOrThrow(ACCESS_TOKEN_COL_ID));
    String value = c.getString(c.getColumnIndexOrThrow(ACCESS_TOKEN_COL_VALUE));

    result[i] = new AccessToken(value, id, serverId);
    c.moveToNext();
}

<强>修改：

if (c.moveToFirst()){
   int rowCount = c.getCount();
   AccessToken[] result = new AccessToken(rowCount);
   int recCount = 0;
   while (!c.isAfterLast()){
        long id = c.getLong(c.getColumnIndexOrThrow(ACCESS_TOKEN_COL_ID));
        String value = c.getString(c.getColumnIndexOrThrow(ACCESS_TOKEN_COL_VALUE));

        result[recCount++] = new AccessToken(value, id, serverId);
        c.moveToNext();
   }
   c.close(); // <-- IMPORTANT!!!!
}

光标找不到列？

2 个答案: