Kotlin实现图片选择器的关键技术点总结

val PROJECTION = arrayOf(
    MediaStore.Files.FileColumns._ID,
    COLUMN_BUCKET_ID,
    COLUMN_BUCKET_DISPLAY_NAME,
    MediaStore.MediaColumns.MIME_TYPE
)

val MATRIX_COLUMNS = arrayOf(
    MediaStore.Files.FileColumns._ID, COLUMN_BUCKET_ID, COLUMN_BUCKET_DISPLAY_NAME, MediaStore.MediaColumns.MIME_TYPE, COLUMN_URI, COLUMN_COUNT
)

{
        return withContext(Dispatchers.Default) {
            // key是对应的文件夹id value 是文件夹下面有几个图片
            val bucketMap = hashMapOf<Long, Long>()
            while (cursor.moveToNext()) {
                val bucketId = cursor.getBucketId()
                if (bucketMap.containsKey(bucketId)) {
                    val count = bucketMap[bucketId]
                    bucketMap[bucketId] = count!! + 1
                } else {
                    bucketMap[bucketId] = 1L
                }
            }

            // 创建虚拟的cursor 从cursor的第二条记录开始
            val matrixCursor = MatrixCursor(MATRIX_COLUMNS)
            // 总文件夹的 cursor 一般取第一张图 作为封面图
            val allAlbumCursor = MatrixCursor(MATRIX_COLUMNS)

            var allAlbumUri: Uri? = null
            var fileId: Long? = null
            if (cursor.moveToFirst()) {
                //取第一张图的 uri
                allAlbumUri = cursor.getUri()
                //取第一张图的fileId
                fileId = cursor.getFileId()
                Log.v("wuyue", "allAlbumUri:$allAlbumUri")
                val bucketIdSet = hashSetOf<Long>()
                do {
                    // 如果之前已经有这个 图片文件夹 则放弃 直接看下一个
                    if (bucketIdSet.contains(cursor.getBucketId())) {
                        continue
                    }


                    var bucketDisplayName = ""
                    if (cursor.getType(cursor.getColumnIndex(COLUMN_BUCKET_DISPLAY_NAME)) == FIELD_TYPE_STRING) {
                        bucketDisplayName = cursor.getBucketDisplayName()
                    } 
                    bucketIdSet.add(cursor.getBucketId())
                    matrixCursor.addRow(arrayOf(cursor.getFileId().toString(), cursor.getBucketId().toString(), bucketDisplayName, cursor.getFileMimeType(), cursor.getUri().toString(), bucketMap[cursor.getBucketId()].toString()))

                } while (cursor.moveToNext())
            }

            allAlbumCursor.addRow(arrayOf(fileId ?: "", "-1", "All", allAlbumUri?.toString() ?: "", "", cursor.count))

            MergeCursor(arrayOf(allAlbumCursor, matrixCursor))
        }
    }

/**
 * 获取图片文件夹的名称
 */
fun Cursor.getBucketDisplayName(): String = getString(getColumnIndex(COLUMN_BUCKET_DISPLAY_NAME))

abstract class RecyclerViewCursorAdapter<VH : RecyclerView.ViewHolder?> internal constructor(c: Cursor?) :
    RecyclerView.Adapter<VH?>() {
    private var mCursor: Cursor? = null
    private var mRowIDColumn = 0
    protected abstract fun onBindViewHolder(holder: VH, cursor: Cursor?)
    override fun onBindViewHolder(holder: VH, position: Int) {
        if (!isDataValid(mCursor)) {
            throw IllegalStateException("Cannot bind view holder when cursor is in invalid state.")
        }
        if (!mCursor!!.moveToPosition(position)) {
            throw IllegalStateException(
                "Could not move cursor to position " + position + " when trying to bind view holder"
            )
        }
        onBindViewHolder(holder, mCursor)
    }

    override fun getItemViewType(position: Int): Int {
        if (!mCursor!!.moveToPosition(position)) {
            throw IllegalStateException(
                ("Could not move cursor to position " + position + " when trying to get item view type.")
            )
        }
        return getItemViewType(position, mCursor)
    }

    protected abstract fun getItemViewType(position: Int, cursor: Cursor?): Int
    override fun getItemCount(): Int {
        return if (isDataValid(mCursor)) {
            mCursor!!.count
        } else {
            0
        }
    }

    override fun getItemId(position: Int): Long {
        if (!isDataValid(mCursor)) {
            throw IllegalStateException("Cannot lookup item id when cursor is in invalid state.")
        }
        if (!mCursor!!.moveToPosition(position)) {
            throw IllegalStateException(
                ("Could not move cursor to position " + position + " when trying to get an item id")
            )
        }
        return mCursor!!.getLong(mRowIDColumn)
    }

    fun swapCursor(newCursor: Cursor?) {
        if (newCursor === mCursor) {
            return
        }
        if (newCursor != null) {
            mCursor = newCursor
            mRowIDColumn = mCursor!!.getColumnIndexOrThrow(MediaStore.Files.FileColumns._ID)
            // notify the observers about the new cursor
            notifyDataSetChanged()
        } else {
            notifyItemRangeRemoved(0, itemCount)
            mCursor = null
            mRowIDColumn = -1
        }
    }

    fun getCursor(): Cursor? {
        return mCursor
    }

    private fun isDataValid(cursor: Cursor?): Boolean {
        return cursor != null && !cursor.isClosed
    }

    init {
        setHasStableIds(true)
        swapCursor(c)
    }
}