Sharing Files笔记

Setting Up File Sharing

为了安全地向别的app提供文件，使用URI是个很好的方法。FielProvider可以为文件生成URI。

指定FileProvider:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="com.example.myapp">    <application        ...>        <provider            android:name="android.support.v4.content.FileProvider"            android:authorities="com.example.myapp.fileprovider"            android:grantUriPermissions="true"            android:exported="false">            <meta-data                android:name="android.support.FILE_PROVIDER_PATHS"                android:resource="@xml/filepaths" />        </provider>        ...    </application></manifest>

android:exported表示你的app声明的FileProvider能否被其他app使用。android:resource表示能够分享文件的目录。

指定可以分享的目录：
在res/xm目录下创建filepaths.xml，在文件中声明目录。<files-path>标签，指定内部存储的files目录；类似的还有<external-path>、<cache-path>标签。代码片段如下：

<paths>    <files-path path="images/" name="myimages" /></paths>

在使用<external-cache-path>时，会报错：Caused by: java.lang.IllegalArgumentException: Failed to find configured root that contains /storage/emulated/0/Android/data/com.addcn.car8891/cache/123.txt。这是什么原因？
原因：FileProvider类支持的标签有<root-path>、<files-path>、<cache-path>、<external-path>，并没有<external-cache-path>。可能是文档有错误，或是版本没有跟上。

注意：XML文件是唯一指定分享目录的方式。

上诉例子，FileProvider返回的URI为content://com.example.myapp.fileprovider/myimages/default_image.jpg。

代码示例

使用FileProvider将文件转化成Uri：

Uri uri=FileProvider.getUriForFile(this,"com.addcn.car8891.fileprovider",new File(getExternalCacheDir(),"123.txt"));    if(mShareActionProvider!=null){        Intent intent=new Intent(Intent.ACTION_SEND);        intent.setType("text/plain");        intent.putExtra(Intent.EXTRA_STREAM,uri);        mShareActionProvider.setShareIntent(intent);    }

可分享文件目录声明：

<paths xmlns:android="http://schemas.android.com/apk/res/android">    <!--<external-cache-path path="" name="haha"/>-->    <external-path path="" name="heihei"/></paths>

Sharing File

Receive File Requests

为了从客户端app接收文件请求，并且用一个content URI作为相应，你的app需要一个提供文件选择的Activity。客户端app用带ACTION_PICK的action，调用startActivityForResult()方法。

Create a File Selection Activity

<manifest xmlns:android="http://schemas.android.com/apk/res/android">    ...        <application>        ...            <activity                android:name=".FileSelectActivity"                android:label="@File Selector" >                <intent-filter>                    <action                        android:name="android.intent.action.PICK"/>                    <category                        android:name="android.intent.category.DEFAULT"/>                    <category                        android:name="android.intent.category.OPENABLE"/>                    <data android:mimeType="text/plain"/>                    <data android:mimeType="image/*"/>                </intent-filter>            </activity>

android.intent.category.OPENABLE表示intent的URI能够被openFileDescriptor(Uri,String)方法开启。

Define the file selection Activity in code

public class MainActivity extends Activity {    // The path to the root of this app's internal storage    private File mPrivateRootDir;    // The path to the "images" subdirectory    private File mImagesDir;    // Array of files in the images subdirectory    File[] mImageFiles;    // Array of filenames corresponding to mImageFiles    String[] mImageFilenames;    // Initialize the Activity    @Override    protected void onCreate(Bundle savedInstanceState) {        ...        // Set up an Intent to send back to apps that request a file        mResultIntent =                new Intent("com.example.myapp.ACTION_RETURN_FILE");        // Get the files/ subdirectory of internal storage        mPrivateRootDir = getFilesDir();        // Get the files/images subdirectory;        mImagesDir = new File(mPrivateRootDir, "images");        // Get the files in the images subdirectory        mImageFiles = mImagesDir.listFiles();        // Set the Activity's result to null to begin with        setResult(Activity.RESULT_CANCELED, null);        /*         * Display the file names in the ListView mFileListView.         * Back the ListView with the array mImageFilenames, which         * you can create by iterating through mImageFiles and         * calling File.getAbsolutePath() for each File         */         ...    }    ...}

Respond to a File Selection

URI权限不能用于Uri.fromFile()方法生成的file://URis，能用于与Content Providers相关的URIs。FileProvider API可以帮助创建这种URIs。

实例代码：

protected void onCreate(Bundle savedInstanceState) {    ...    // Define a listener that responds to clicks on a file in the ListView    mFileListView.setOnItemClickListener(        new AdapterView.OnItemClickListener() {        @Override        /*        * When a filename in the ListView is clicked, get its         * content URI and send it to the requesting app         */        public void onItemClick(AdapterView<?> adapterView,        View view,int position,long rowId) {            /*             * Get a File for the selected file name.             * Assume that the file names are in the             * mImageFilename array.             */            File requestFile = new File(mImageFilename[position]);            /*             * Most file-related method calls need to be in             * try-catch blocks.             */            // Use the FileProvider to get a content URI            try {                fileUri = FileProvider.getUriForFile(                    MainActivity.this,"com.example.myapp.fileprovider",                        requestFile);                } catch (IllegalArgumentException e) {                    Log.e("File Selector",                          "The selected file can't be shared: " +                          clickedFilename);                }                ...        }    });        ...}

Grant Permission for the File

要使content URI能够访问或修改数据，还必须对客户端app进行授权。授权的方式有：

• 在<provider/>里通过android:grantUriPermissions、android:readPermission、android:writePermission属性，或<grant-uri-permission>标签进行授权。
• Intent设置了URI,比如调用setData(Uri)，调用Intent的addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION)进行授权。接收app的任务栈结束时，权限自动撤销。
• 通过Context.grantUriPermission()方法给content URI授权。有个缺点是撤销权限需要调用Context.revokeUriPermission()方法。

Share the File with the Requesting App

代码片段如下：

protected void onCreate(Bundle savedInstanceState) {    ...    // Define a listener that responds to clicks on a file in the ListView    mFileListView.setOnItemClickListener(        new AdapterView.OnItemClickListener() {        @Override        public void onItemClick(AdapterView<?> adapterView,            View view,int position,long rowId) {                ...                if (fileUri != null) {                    ...                    // Put the Uri and MIME type in the result Intent                    mResultIntent.setDataAndType(                            fileUri,                            getContentResolver().getType(fileUri));                    // Set the result                    MainActivity.this.setResult(Activity.RESULT_OK,                            mResultIntent);                    } else {                        mResultIntent.setDataAndType(null, "");                        MainActivity.this.setResult(RESULT_CANCELED,                                mResultIntent);                    }                }    });

Requesting a Shared File

代码示例：

public class MainActivity extends Activity {    private Intent mRequestFileIntent;    private ParcelFileDescriptor mInputPFD;    ...    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mRequestFileIntent = new Intent(Intent.ACTION_PICK);        mRequestFileIntent.setType("image/jpg");        ...    }    ...    protected void requestFile() {        /**         * When the user requests a file, send an Intent to the         * server app.         * files.         */            startActivityForResult(mRequestFileIntent, 0);        ...    }    ...}

Access the Requested File

代码示例：

/*     * When the Activity of the app that hosts files sets a result and calls     * finish(), this method is invoked. The returned Intent contains the     * content URI of a selected file. The result code indicates if the     * selection worked or not.     */    @Override    public void onActivityResult(int requestCode, int resultCode,            Intent returnIntent) {        // If the selection didn't work        if (resultCode != RESULT_OK) {            // Exit without doing anything else            return;        } else {            // Get the file's content URI from the incoming Intent            Uri returnUri = returnIntent.getData();            /*             * Try to open the file for "read" access using the             * returned URI. If the file isn't found, write to the             * error log and return.             */            try {                /*                 * Get the content resolver instance for this context, and use it                 * to get a ParcelFileDescriptor for the file.                 */                mInputPFD = getContentResolver().openFileDescriptor(returnUri, "r");            } catch (FileNotFoundException e) {                e.printStackTrace();                Log.e("MainActivity", "File not found.");                return;            }            // Get a regular file descriptor for the file            FileDescriptor fd = mInputPFD.getFileDescriptor();            ...        }    }

openFileDescriptor()方法的第二个参数是使用的文件模式，r表示读,w表示写，rw表示读写。

Retrieving File Information

Retrieve a File’s MIME Type

代码示例：

.../* * Get the file's content URI from the incoming Intent, then * get the file's MIME type */Uri returnUri = returnIntent.getData();String mimeType = getContentResolver().getType(returnUri);...

Retrieve a File’s Name and Size

FileProvider类默认实现的query()方法返回的Cursor有连个列名：

• DISPLAY_NAME 文件名。
• SIZE 文件字节数。

示例代码：

.../* * Get the file's content URI from the incoming Intent, * then query the server app to get the file's display name * and size. */Uri returnUri = returnIntent.getData();Cursor returnCursor =    getContentResolver().query(returnUri, null, null, null, null);/* * Get the column indexes of the data in the Cursor, * move to the first row in the Cursor, get the data, * and display it. */int nameIndex = returnCursor.getColumnIndex(OpenableColumns.DISPLAY_NAME);int sizeIndex = returnCursor.getColumnIndex(OpenableColumns.SIZE);returnCursor.moveToFirst();TextView nameView = (TextView) findViewById(R.id.filename_text);TextView sizeView = (TextView) findViewById(R.id.filesize_text);nameView.setText(returnCursor.getString(nameIndex));sizeView.setText(Long.toString(returnCursor.getLong(sizeIndex)));...