Android的ContentResolver.query（）传递一个字符串[]投影参数时抛出异常 [英] Android ContentResolver.query() throwing exception when passing a String[] projection argument

问题描述

在我目前的Andr​​oid项目中，我面临着一个奇怪的错误。

In my current Android project I'm facing with a strange error.

每次我发出<一个href=\"https://developer.android.com/reference/android/content/ContentResolver.html#query(android.net.Uri,%20java.lang.String[],%20java.lang.String,%20java.lang.String[],%20java.lang.String)\"相对=nofollow>查询方法我得到的错误说，通过投影的列的String []的说法是不存在的（_id列字段组成）。尽管如此，传递null （因此允许将返回所有列）的正常工作，所以我必须承担这不是列名不匹配的问题。此外，从Cursor对象检索数据时，列名不给予任何问题，因为我可以放心地通过查询指定相同的列名（）获取的所有数据。

Everytime I issue the query method I get errors saying that the columns of the passed projection String[] argument don't exist (_id column field comprised). Despite this, passing null (hence allowing all columns to be returned) works fine, so I must assume this is not a problem of column names mismatch. Also, when retrieving data from a Cursor object, the column names are not giving any problems, since I can safely get all of the data by specifying the same column names on query().

我目前查询的MediaStore.Audio *数据库和清单文件中的所有权限和最终的设置都OK。

I'm currently querying on the MediaStore.Audio.* database, and all the permissions within the Manifest file and eventual settings are ok.

这是我的code片断：

This is my code snippet:

  Cursor        artists[] = new Cursor[2];

        String  projection[] = {
                Audio.Artists.ARTIST,
                Audio.Artists.NUMBER_OF_ALBUMS,
                Audio.Artists.NUMBER_OF_TRACKS,
        };

    artists[0] = this.getActivity().getApplicationContext().getContentResolver().query(
                    Audio.Artists.INTERNAL_CONTENT_URI,
                    projection,
                    null,
                    null,
                    Audio.Artists.DEFAULT_SORT_ORDER
                    );

    artists[1] = this.getActivity().getApplicationContext().getContentResolver().query(
                    Audio.Artists.EXTERNAL_CONTENT_URI,
                    projection,
                    null,
                    null,
                    Audio.Artists.DEFAULT_SORT_ORDER
                    );

            this.adapter = new ArtistListAdapter(this.getActivity(), new MergeCursor(artists));

只是要清楚，这里就是我使用光标对象：

Just to make it clear, here's where I use the Cursor object:

@Override
public void bindView (View v, Context c, Cursor cursor) {
    ImageView   icon;
    TextView    name, artistInfo;

    //icon = (ImageView) v.findViewById(R.id.artist_icon);
    name = (TextView) v.findViewById(R.id.artist_name);
    artistInfo = (TextView) v.findViewById(R.id.artist_info);

    //icon.setIcon(icon);
    name.setText(cursor.getString(cursor.getColumnIndex(Audio.Artists.ARTIST)));
    artistInfo.setText(
            String.format(
                    "%s total albums\n%s total songs",
                    cursor.getString(cursor.getColumnIndex(Audio.Artists.NUMBER_OF_ALBUMS)),
                    cursor.getString(cursor.getColumnIndex(Audio.Artists.NUMBER_OF_TRACKS))
            )
    );
}

发出此code，我收到以下错误：

Issuing this code, I receive the following error:

07-11 21:28:31.221: E/AndroidRuntime(22737): FATAL EXCEPTION: main
07-11 21:28:31.221: E/AndroidRuntime(22737): java.lang.IllegalArgumentException: column '_id' does not exist
07-11 21:28:31.221: E/AndroidRuntime(22737):    at android.database.AbstractCursor.getColumnIndexOrThrow(AbstractCursor.java:303)
07-11 21:28:31.221: E/AndroidRuntime(22737):    at android.support.v4.widget.CursorAdapter.init(CursorAdapter.java:174)

有什么可以成为这个问题的原因以及如何解决？到现在为止，我一直在传递投影参数为空，但我不想要检索我不会使用的内容。

What can be the cause of this problem and how can I fix it? Until now, I've been passing null on the projection arguments, but I don't want to retrieve content I won't be using.

请询问您是否需要进一步的信息。

Please ask if you need further informations.

推荐答案

添加BaseColumns._ID投影阵列。这是使用的CursorAdapter时所需的列（我从您正在使用SimpleCursorAdapter上下文假设）

add BaseColumns._ID to projection array. this is the required column when using the CursorAdapter (and i'm assuming from the context that you are using SimpleCursorAdapter)

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