Building Apps with Content Sharing

  • Sharing Simple Data
    • Intent && ActionProvider
    • 发送数据（发起intent调起其他app处理）
      • Send Text Content
      • Send Binary Content
      • Send Multiple Pieces of Content
    • 接收数据
      • AndroidManifest.xml中为Activity定义<intent-filter>
      • 在Activity的onCreate中调用getIntent()获取action、数据，并进行处理
  • Sharing Files
    • 唯一“安全”的方式就是：将文件对应的URI通过Intent发送出去，并为该URI提供临时的访问权限。而这些步骤都可以通过FileProvider完成
    • 在AndroidManifest.xml中声明provider
      <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>
    • <meta-data>指定描述要分享的目录的xml文件
    • 指定要分享的目录
      <paths>
  <files-path path="images/" name="myimages" />
</paths>
    • <paths>标签可以有多个子标签，<files-path>指定app的files目录下的分享目录名，<external-path>指定外部存储（Environment.getExternalStorageDirectory()）的分享目录名，<cache-path>指定app的cache目录下的分享目录名；分享路径只能在xml中描述；
    • 如上配置后，需要访问files/images/default_image.jpg时，对应uri为：content://com.example.myapp.fileprovider/myimages/default_image.jpg
    • Receive File Requests
      • 定义一个Selection Activity，响应Intent action，例如：ACTION_PICK
        <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>
      • 其他app发起该intent，通过startActivityForResult()和onActivityResult()中发起请求、处理结果
      • 在Selection Activity的onCreate函数中，解析其他app的请求
        File requestFile = new File(mImageFilename[position]);
// 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);
}
      • 赋予临时访问权限
        mResultIntent = new Intent("com.example.myapp.ACTION_RETURN_FILE");
if (fileUri != null) {
   // Grant temporary read permission to the content URI
   mResultIntent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
}
      • 使用setFlags()赋予临时访问权限更安全，Context.grantUriPermission()赋予的权限只有手动调用Context.revokeUriPermission()才会被移除
      • 返回结果
        mResultIntent.setDataAndType(
       fileUri,
       getContentResolver().getType(fileUri));
// Set the result
MainActivity.this.setResult(Activity.RESULT_OK,
       mResultIntent);
finish();
    • Requesting a Shared File
      • 通常流程是：app发起一个带有请求的intent，分享文件的app的相应Activity被启动，该Activity显示文件列表，用户选择文件后返回被选中的文件的Uri
      • 发起请求
        mRequestFileIntent = new Intent(Intent.ACTION_PICK);
mRequestFileIntent.setType("image/jpg");
startActivityForResult(mRequestFileIntent, 0);
      • 访问返回的文件
        @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();
       ...
   }
}
    • Retrieving File Information
      • MIME Type
        Uri returnUri = returnIntent.getData();
String mimeType = getContentResolver().getType(returnUri);
      • File's Name and Size
        Uri returnUri = returnIntent.getData();
Cursor returnCursor =
   getContentResolver().query(returnUri, null, null, null, null);
int nameIndex = returnCursor.getColumnIndex(OpenableColumns.DISPLAY_NAME);
int sizeIndex = returnCursor.getColumnIndex(OpenableColumns.SIZE);
nameView.setText(returnCursor.getString(nameIndex));
sizeView.setText(Long.toString(returnCursor.getLong(sizeIndex)));

  • Sharing Files with NFC

    • Android Beam，大文件传输，from 4.1 API 16
    • Android Beam NDEF，小数据传输，from 4.0 API 14

    • 发送文件

      • 权限：<uses-permission android:name="android.permission.NFC" />，<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
      • NFC feature：<uses-feature android:name="android.hardware.nfc" android:required="true" />
      • minSdkVersion >= 16
      • 检查是否支持
        if (PackageManager.hasSystemFeature(PackageManager.FEATURE_NFC) &&
       Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
   mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
}

      • 创建提供文件的回调

        // List of URIs to provide to Android Beam
private Uri[] mFileUris = new Uri[10];
...
/**
* Callback that Android Beam file transfer calls to get
* files to share
*/
private class FileUriCallback implements
       NfcAdapter.CreateBeamUrisCallback {
   public FileUriCallback() {
   }
   /**
   * Create content URIs as needed to share with another device
   */
   @Override
   public Uri[] createBeamUris(NfcEvent event) {
       return mFileUris;
   }
}

...
// Android Beam file transfer is available, continue
...
mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
/*
* Instantiate a new FileUriCallback to handle requests for
* URIs
*/
mFileUriCallback = new FileUriCallback();
// Set the dynamic callback for URI requests.
mNfcAdapter.setBeamPushUrisCallback(mFileUriCallback,this);
...
      • 设置需要发送的文件
        /*
* Create a list of URIs, get a File,
* and set its permissions
*/
private Uri[] mFileUris = new Uri[10];
String transferFile = "transferimage.jpg";
File extDir = getExternalFilesDir(null);
File requestFile = new File(extDir, transferFile);
requestFile.setReadable(true, false);
// Get a URI for the File and add it to the list of URIs
fileUri = Uri.fromFile(requestFile);
if (fileUri != null) {
   mFileUris[0] = fileUri;
} else {
   Log.e("My Activity", "No File URI available for file.");
}
    • 接收文件
      • 设置intent-filter
        <activity
   android:name="com.example.android.nfctransfer.ViewActivity"
   android:label="Android Beam Viewer" >
   ...
   <intent-filter>
       <action android:name="android.intent.action.VIEW"/>
       <category android:name="android.intent.category.DEFAULT"/>
       ...
   </intent-filter>
</activity>
      • 权限：<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
      • 获取接收文件的路径
        // Get the Intent action
mIntent = getIntent();
String action = mIntent.getAction();
/*
* For ACTION_VIEW, the Activity is being asked to display data.
* Get the URI.
*/
if (TextUtils.equals(action, Intent.ACTION_VIEW)) {
   // Get the URI from the Intent
   Uri beamUri = mIntent.getData();
   /*
    * Test for the type of URI, by getting its scheme value
    */
   if (TextUtils.equals(beamUri.getScheme(), "file")) {
       mParentPath = handleFileUri(beamUri);
   } else if (TextUtils.equals(
           beamUri.getScheme(), "content")) {
       mParentPath = handleContentUri(beamUri);
   }
}
      • 读取
        String fileName = beamUri.getPath();
File copiedFile = new File(fileName);
      • 根据不同的content provider读取文件
        ...
public String handleContentUri(Uri beamUri) {
   // Position of the filename in the query Cursor
   int filenameIndex;
   // File object for the filename
   File copiedFile;
   // The filename stored in MediaStore
   String fileName;
   // Test the authority of the URI
   if (!TextUtils.equals(beamUri.getAuthority(), MediaStore.AUTHORITY)) {
       /*
       * Handle content URIs for other content providers
       */
   // For a MediaStore content URI
   } else {
       // Get the column that contains the file name
       String[] projection = { MediaStore.MediaColumns.DATA };
       Cursor pathCursor =
               getContentResolver().query(beamUri, projection,
               null, null, null);
       // Check for a valid cursor
       if (pathCursor != null &&
               pathCursor.moveToFirst()) {
           // Get the column index in the Cursor
           filenameIndex = pathCursor.getColumnIndex(
                   MediaStore.MediaColumns.DATA);
           // Get the full file name including path
           fileName = pathCursor.getString(filenameIndex);
           // Create a File object for the filename
           copiedFile = new File(fileName);
           // Return the parent directory of the file
           return new File(copiedFile.getParent());
       } else {
           // The query didn't work; return null
           return null;
       }
   }
}
...

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