Building Apps with Content Sharing 官方开发手册 -Android&Java 技术笔记集册

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;
          }
      }
  }
  ...

Building Apps with Content Sharing

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