android.database.CursorIndexOutOfBoundsException:Index -1 requested, with a size of 1

android.database.CursorIndexOutOfBoundsException:Index -1 requested, with a size of 1

android 中数据库处理，特别是使用cursor时，注意初始位置，好像是从下标为-1的地方开始的，也就是说一次查询中，返回给cursor查询结果时，不能够马上从cursor中提取值。

比如,下面的代码会返回错误，android.database.CursorIndexOutOfBoundsException:Index -1 requested, with a size of 0：

<p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px;"><span style="font-size: 18px;"><span class="kwd">int</span><span class="pln"> score </span><span class="pun">=</span><span class="pln"> </span><span class="pun">((</span><span class="typ">Cursor</span><span class="pun">)</span><span class="pln">getReadableDatabase</span><span class="pun">().</span><span class="pln">query</span><span class="pun">(</span><span class="pln">TABLE_NAME</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">String</span><span class="pun">[]{</span><span class="str">"learned"</span><span class="pun">},</span><span class="pln"> </span><span class="str">"_id=?"</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">String</span><span class="pun">[]{</span><span class="str">""</span><span class="pun">+</span><span class="pln">id</span><span class="pun">},</span><span class="pln"> </span><span class="kwd">null</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">null</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">null</span><span class="pun">,</span><span class="str">"1"</span><span class="pun">)).</span><span class="pln">getInt</span><span class="pun">(</span><span class="lit">0</span><span class="pun">);</span></span></p>

正确的用法：

<p style="margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px;"><span style="font-size: 18px;"><span class="pln">  </span><span class="typ">Cursor</span><span class="pln"> cursor </span><span class="pun">=</span><span class="pln"> getReadableDatabase</span><span class="pun">().</span><span class="pln">query</span><span class="pun">(</span><span class="pln">TABLE_NAME</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">String</span><span class="pun">[]{</span><span class="str">"learned"</span><span class="pun">},</span><span class="pln"> </span><span class="str">"_id=?"</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">String</span><span class="pun">[]{</span><span class="str">""</span><span class="pun">+</span><span class="pln">id</span><span class="pun">},</span><span class="pln"> </span><span class="kwd">null</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">null</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">null</span><span class="pun">,</span><span class="str">"1"</span><span class="pun">);</span><span class="pln">  </span><span class="kwd">int</span><span class="pln"> learned</span><span class="pun">=</span><span class="lit">0</span><span class="pun">;</span><span class="pln">  </span><span class="kwd">if</span><span class="pun">(</span><span class="pln">cursor</span><span class="pun">.</span><span class="pln">moveToFirst</span><span class="pun">()){</span><span class="pln">   score</span><span class="pun">=</span><span class="pln"> cursor</span><span class="pun">.</span><span class="pln">getInt</span><span class="pun">(</span><span class="lit">0</span><span class="pun">);</span><span class="pln">  </span><span class="pun">}</span><span class="pln">  cursor</span><span class="pun">.</span><span class="pln">close</span><span class="pun">();</span></span></p><div><span style="font-size: 18px;"><span class="pun"></span></span></div>