• Intent && ActionProvider
• 發(fā)送數(shù)據(jù)（發(fā)起intent調(diào)起其他app處理）
  • Send Text Content
  • Send Binary Content
  • Send Multiple Pieces of Content
• 接收數(shù)據(jù)
  • AndroidManifest.xml中為Activity定義<intent-filter>
  • 在Activity的onCreate中調(diào)用getIntent()獲取action、數(shù)據(jù)，并進(jìn)行處理

• 唯一“安全”的方式就是：將文件對(duì)應(yīng)的URI通過(guò)Intent發(fā)送出去，并為該URI提供臨時(shí)的訪問(wèn)權(quán)限。而這些步驟都可以通過(guò)FileProvider完成
• 在AndroidManifest.xml中聲明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錄的xml文件
• 指定要分享的目錄

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

• <paths>標(biāo)簽可以有多個(gè)子標(biāo)簽，<files-path>指定app的files目錄下的分享目錄名，<external-path>指定外部存儲(chǔ)（Environment.getExternalStorageDirectory()）的分享目錄名，<cache-path>指定app的cache目錄下的分享目錄名；分享路徑只能在xml中描述；
• 如上配置后，需要訪問(wèn)files/images/default_image.jpg時(shí)，對(duì)應(yīng)uri為：content://com.example.myapp.fileprovider/myimages/default_image.jpg
• Receive File Requests
  • 定義一個(gè)Selection Activity，響應(yīng)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發(fā)起該intent，通過(guò)startActivityForResult()和onActivityResult()中發(fā)起請(qǐng)求、處理結(jié)果
  • 在Selection Activity的onCreate函數(shù)中，解析其他app的請(qǐng)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);
      }

  • 賦予臨時(shí)訪問(wèn)權(quán)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()賦予臨時(shí)訪問(wèn)權(quán)限更安全，Context.grantUriPermission()賦予的權(quán)限只有手動(dòng)調(diào)用Context.revokeUriPermission()才會(huì)被移除
  • 返回結(jié)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發(fā)起一個(gè)帶有請(qǐng)求的intent，分享文件的app的相應(yīng)Activity被啟動(dòng)，該Activity顯示文件列表，用戶選擇文件后返回被選中的文件的Uri
  • 發(fā)起請(qǐng)求

      mRequestFileIntent = new Intent(Intent.ACTION_PICK);
      mRequestFileIntent.setType("image/jpg");
      startActivityForResult(mRequestFileIntent, 0);

  • 訪問(wèn)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，大文件傳輸，from 4.1 API 16
• Android Beam NDEF，小數(shù)據(jù)傳輸，from 4.0 API 14

• 發(fā)送文件

  • 權(quán)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
  • 檢查是否支持

      if (PackageManager.hasSystemFeature(PackageManager.FEATURE_NFC) &&
              Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
          mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
      }

  • 創(chuàng)建提供文件的回調(diào)

      // 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);
      ...

  • 設(shè)置需要發(fā)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
  • 設(shè)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>

  • 權(quán)限：<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
  • 獲取接收文件的路徑

      // 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);
          }
      }

  • 讀取

      String fileName = beamUri.getPath();
      File copiedFile = new File(fileName);

  • 根據(jù)不同的content provider讀取文件

      ...
      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;
              }
          }
      }
      ...