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Android - KitKat 以上版本從 URI 取得檔案實體路徑

2016-05-26 9:42 AM

有時使用檔案選擇器取得路徑時會發現路徑是奇怪的 content://downloads/public_downloads 字串

而這種路徑使用 context.getContentResolver().query(); 方法取得的路徑會是空的

其實是因為新版 Android 在路徑上是使用 uri 的方式表示的

有點像網址,好處是同一個 uri 可以指定到不同的實體路徑內

用以對應不同的開發商與使用者設定

壞處就是取得路徑的方法變得較麻煩(而且官方文件似乎找不到方法? WTF?)

而且很多類型的檔案取得路徑的方式也沒有統一

以下就是對應各版本(4.4 以上)取得路徑的 FileUtil 的原始碼

檔案瀏覽器的使用方式可以到 啟動檔案瀏覽器選擇檔案 教學查看

程式碼範例
import android.content.ContentUris;
import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.os.Environment;
import android.provider.DocumentsContract;
import android.provider.MediaStore;
import cmc.toolkit.FileKit;
import com.ihad.ptt.model.exception.EmptyFilePathException;
import com.ihad.ptt.model.exception.IllegalTrueTypeFontException;

import java.io.File;
import java.io.FileNotFoundException;

public class FileUtils {

    /**
     * 從 uri 取得檔案路徑 這將從 Storage Access Framework Documents 取得路徑
     * 也會使用從 _data 欄位取得 MediaStore 以及其他 file-based ContentProviders 的對應路徑
     *
     * @param context The context.
     * @param uri The Uri to query.
     * @author paulburke
     */
    public static String getPath(final Context context, final Uri uri) {

        // DocumentProvider
        if ( DocumentsContract.isDocumentUri(context, uri) ) {
            // ExternalStorageProvider
            if (isExternalStorageDocument(uri)) {
                final String docId = DocumentsContract.getDocumentId(uri);
                final String[] split = docId.split(":");
                final String type = split[0];

                if ("primary".equalsIgnoreCase(type)) {
                    String path = Environment.getExternalStorageDirectory().getPath();

                    if (split.length > 1) {
                        path += "/" + split[1];
                    }

                    return path;
                }
                else {
                    String path;
                    if (Environment.isExternalStorageRemovable()) {
                        path = System.getenv("EXTERNAL_STORAGE");
                    } else {
                        path = System.getenv("SECONDARY_STORAGE");
                        if (path == null || path.length() == 0) {
                            path = System.getenv("EXTERNAL_SDCARD_STORAGE");
                        }
                    }

                    if (split.length > 1) {
                        path += "/" + split[1];
                    }

                    return path;
                }
            }
            // DownloadsProvider
            else if (isDownloadsDocument(uri)) {

                final String id = DocumentsContract.getDocumentId(uri);
                final Uri contentUri = ContentUris.withAppendedId(
                        Uri.parse("content://downloads/public_downloads"), Long.valueOf(id));

                return getDataColumn(context, contentUri, null, null);
            }
            // MediaProvider
            else if (isMediaDocument(uri)) {
                final String docId = DocumentsContract.getDocumentId(uri);
                final String[] split = docId.split(":");
                final String type = split[0];

                Uri contentUri = null;
                if ("image".equals(type)) {
                    contentUri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
                } else if ("video".equals(type)) {
                    contentUri = MediaStore.Video.Media.EXTERNAL_CONTENT_URI;
                } else if ("audio".equals(type)) {
                    contentUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
                }

                final String selection = "_id=?";
                final String[] selectionArgs = new String[] {
                        split[1]
                };

                return getDataColumn(context, contentUri, selection, selectionArgs);
            }
        }
        // MediaStore (and general)
        else if ("content".equalsIgnoreCase(uri.getScheme())) {
            // Return the remote address
            if (isGooglePhotosUri(uri)) return uri.getLastPathSegment();

            return getDataColumn(context, uri, null, null);
        }
        // File
        else if ("file".equalsIgnoreCase(uri.getScheme())) {
            return uri.getPath();
        }

        return null;
    }

    /**
     * 從 data 欄位取得 uri 對應的實體路徑
     * 主要用以取得 MediaStore Uris 以及其他 file-based ContentProviders 的對應路徑
     *
     * @param context The context.
     * @param uri The Uri to query.
     * @param selection (Optional) Filter used in the query.
     * @param selectionArgs (Optional) Selection arguments used in the query.
     * @return The value of the _data column, which is typically a file path.
     * @author paulburke
     */
    public static String getDataColumn(Context context, Uri uri, String selection,
                                       String[] selectionArgs) {

        Cursor cursor = null;
        final String column = "_data";
        final String[] projection = {
                column
        };

        try {
            cursor = context.getContentResolver().query(uri, projection, selection, selectionArgs,
                    null);
            if (cursor != null && cursor.moveToFirst()) {
                final int column_index = cursor.getColumnIndexOrThrow(column);
                return cursor.getString(column_index);
            }
        } finally {
            if (cursor != null)
                cursor.close();
        }
        return null;
    }


    /**
     * @param uri The Uri to check.
     * @return 是否為 ExternalStorageProvider 類型的 uri
     * @author paulburke
     */
    public static boolean isExternalStorageDocument(Uri uri) {
        return "com.android.externalstorage.documents".equals(uri.getAuthority());
    }

    /**
     * @param uri The Uri to check.
     * @return 是否為 DownloadsProvider 類型的 uri
     * @author paulburke
     */
    public static boolean isDownloadsDocument(Uri uri) {
        return "com.android.providers.downloads.documents".equals(uri.getAuthority());
    }

    /**
     * @param uri The Uri to check.
     * @return MediaProvider 類型的 uri
     * @author paulburke
     */
    public static boolean isMediaDocument(Uri uri) {
        return "com.android.providers.media.documents".equals(uri.getAuthority());
    }

    /**
     * @param uri The Uri to check.
     * @return 是否為 Google Photos 類型的 uri
     */
    public static boolean isGooglePhotosUri(Uri uri) {
        return "com.google.android.apps.photos.content".equals(uri.getAuthority());
    }

    // 檢查檔案類型的小範例

    /**
     * 檢查取回的檔案副檔名
     * @param path  檔案路徑
     * @return
     *  若檔案類型正確則回傳檔案名稱, 反之則回傳空字串
     * @throws EmptyFilePathException 路徑是空字串或是 null 物件
     * @throws FileNotFoundException 檔案不存在
     * @throws IllegalTrueTypeFontException 檔案類型不正確
     */
    public static String typefaceChecker(String path) throws EmptyFilePathException, FileNotFoundException, IllegalTrueTypeFontException {
        if( path == null || path.isEmpty() ){
            throw new EmptyFilePathException( "File path is empty" );
        }

        File file = new File(path);

        if( !file.exists() || !file.isFile() ) {
            throw new FileNotFoundException( "File path : " + path );
        }

        String filename = file.getName();
        String ext      = FileKit.getFileExt(filename);

        if( !ext.equalsIgnoreCase(".ttf") ){
            throw new IllegalTrueTypeFontException( "File path : " + path + ", File name : " + filename + ", ext : " + ext );
        }

        return filename;
    }
}
各項資料連結
啟動檔案瀏覽器選擇檔案
Stackoverflow - Get real path from URI, Android KitKat new storage access framework
GitHub - aFileChooser

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