Android WebView 上传文件支持全解析

默认情况下情况下，使用Android的WebView是不能够支持上传文件的。而这个，也是在我们的前端工程师告知之后才了解的。因为Android的每个版本WebView的实现有差异，因此需要对不同版本去适配。花了一点时间，参考别人的代码，这个问题已经解决，这里把我踩过的坑分享出来。
主要思路是重写WebChromeClient，然后在WebViewActivity中接收选择到的文件Uri，传给页面去上传就可以了。
创建一个WebViewActivity的内部类

public class XHSWebChromeClient extends WebChromeClient {

  // For Android 3.0+
  public void openFileChooser(ValueCallback<Uri> uploadMsg) {
    CLog.i("UPFILE", "in openFile Uri Callback");
    if (mUploadMessage != null) {
      mUploadMessage.onReceiveValue(null);
    }
    mUploadMessage = uploadMsg;
    Intent i = new Intent(Intent.ACTION_GET_CONTENT);
    i.addCategory(Intent.CATEGORY_OPENABLE);
    i.setType("*/*");
    startActivityForResult(Intent.createChooser(i, "File Chooser"), FILECHOOSER_RESULTCODE);
  }

  // For Android 3.0+
  public void openFileChooser(ValueCallback uploadMsg, String acceptType) {
    CLog.i("UPFILE", "in openFile Uri Callback has accept Type" + acceptType);
    if (mUploadMessage != null) {
      mUploadMessage.onReceiveValue(null);
    }
    mUploadMessage = uploadMsg;
    Intent i = new Intent(Intent.ACTION_GET_CONTENT);
    i.addCategory(Intent.CATEGORY_OPENABLE);
    String type = TextUtils.isEmpty(acceptType) ? "*/*" : acceptType;
    i.setType(type);
    startActivityForResult(Intent.createChooser(i, "File Chooser"),
        FILECHOOSER_RESULTCODE);
  }

  // For Android 4.1
  public void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType, String capture) {
    CLog.i("UPFILE", "in openFile Uri Callback has accept Type" + acceptType + "has capture" + capture);
    if (mUploadMessage != null) {
      mUploadMessage.onReceiveValue(null);
    }
    mUploadMessage = uploadMsg;
    Intent i = new Intent(Intent.ACTION_GET_CONTENT);
    i.addCategory(Intent.CATEGORY_OPENABLE);
    String type = TextUtils.isEmpty(acceptType) ? "*/*" : acceptType;
    i.setType(type);
    startActivityForResult(Intent.createChooser(i, "File Chooser"), FILECHOOSER_RESULTCODE);
  }

//Android 5.0+
  @Override
  @SuppressLint("NewApi")
  public boolean onShowFileChooser(WebView webView, ValueCallback<Uri[]> filePathCallback, FileChooserParams fileChooserParams) {
    if (mUploadMessage != null) {
      mUploadMessage.onReceiveValue(null);
    }
    CLog.i("UPFILE", "file chooser params：" + fileChooserParams.toString());
    mUploadMessage = filePathCallback;
    Intent i = new Intent(Intent.ACTION_GET_CONTENT);
    i.addCategory(Intent.CATEGORY_OPENABLE);
    if (fileChooserParams != null && fileChooserParams.getAcceptTypes() != null
        && fileChooserParams.getAcceptTypes().length > 0) {
      i.setType(fileChooserParams.getAcceptTypes()[0]);
    } else {
      i.setType("*/*");
    }
    startActivityForResult(Intent.createChooser(i, "File Chooser"), FILECHOOSER_RESULTCODE);
    return true;
  }
}

上面openFileChooser是系统未暴露的接口，因此不需要加Override的注解，同时不同版本有不同的参数，其中的参数，第一个ValueCallback用于我们在选择完文件后，接收文件回调到网页内处理，acceptType为接受的文件mime type。在Android 5.0之后，系统提供了onShowFileChooser来让我们实现选择文件的方法，仍然有ValueCallback，在FileChooserParams参数中，同样包括acceptType。我们可以根据acceptType，来打开系统的或者我们自己创建文件选择器。当然如果需要打开相机拍照，也可以自己去使用打开相机拍照的Intent去打开即可。
处理选择的文件
以上是打开响应的选择文件的界面，我们还需要处理接收到文件之后，传给网页来响应。因为我们前面是使用startActivityForResult来打开的选择页面，我们会在onActivityResult中接收到选择的结果。Show code：

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
  super.onActivityResult(requestCode, resultCode, data);
  if (requestCode == FILECHOOSER_RESULTCODE) {
    if (null == mUploadMessage) return;
    Uri result = data == null || resultCode != RESULT_OK ? null : data.getData();
    if (result == null) {
      mUploadMessage.onReceiveValue(null);
      mUploadMessage = null;
      return;
    }
    CLog.i("UPFILE", "onActivityResult" + result.toString());
    String path = FileUtils.getPath(this, result);
    if (TextUtils.isEmpty(path)) {
      mUploadMessage.onReceiveValue(null);
      mUploadMessage = null;
      return;
    }
    Uri uri = Uri.fromFile(new File(path));
    CLog.i("UPFILE", "onActivityResult after parser uri:" + uri.toString());
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
      mUploadMessage.onReceiveValue(new Uri[]{uri});
    } else {
      mUploadMessage.onReceiveValue(uri);
    }

    mUploadMessage = null;
  }
}

以上代码主要就是调用ValueCallback的onReceiveValue方法，将结果传回web。
注意，其他要说的，重要
由于不同版本的差别，Android 5.0以下的版本，ValueCallback 的onReceiveValue接收的参数类型是Uri, 5.0及以上版本接收的是Uri数组，在传值的时候需要注意。
选择文件会使用系统提供的组件或者其他支持的app，返回的uri有的直接是文件的url，有的是contentprovider的uri，因此我们需要统一处理一下，转成文件的uri，可参考以下代码（获取文件的路径）。
调用getPath可以将Uri转成真实文件的Path，然后可以自己生成文件的Uri

public class FileUtils {
  /**
   * @param uri The Uri to check.
   * @return Whether the Uri authority is ExternalStorageProvider.
   */
  public static boolean isExternalStorageDocument(Uri uri) {
    return "com.android.externalstorage.documents".equals(uri.getAuthority());
  }

  /**
   * @param uri The Uri to check.
   * @return Whether the Uri authority is DownloadsProvider.
   */
  public static boolean isDownloadsDocument(Uri uri) {
    return "com.android.providers.downloads.documents".equals(uri.getAuthority());
  }

  /**
   * @param uri The Uri to check.
   * @return Whether the Uri authority is MediaProvider.
   */
  public static boolean isMediaDocument(Uri uri) {
    return "com.android.providers.media.documents".equals(uri.getAuthority());
  }

  /**
   * Get the value of the data column for this Uri. This is useful for
   * MediaStore Uris, and other file-based ContentProviders.
   *
   * @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.
   */
  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;
  }

  /**
   * Get a file path from a Uri. This will get the the path for Storage Access
   * Framework Documents, as well as the _data field for the MediaStore and
   * other file-based ContentProviders.
   *
   * @param context The context.
   * @param uri The Uri to query.
   * @author paulburke
   */
  @SuppressLint("NewApi")
  public static String getPath(final Context context, final Uri uri) {

    final boolean isKitKat = Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT;

    // DocumentProvider
    if (isKitKat && 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)) {
          return Environment.getExternalStorageDirectory() + "/" + split[1];
        }

        // TODO handle non-primary volumes
      }
      // 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 getDataColumn(context, uri, null, null);
    }
    // File
    else if ("file".equalsIgnoreCase(uri.getScheme())) {
      return uri.getPath();
    }

    return null;
  }

}

再有，即使获取的结果为null，也要传给web，即直接调用mUploadMessage.onReceiveValue(null),否则网页会阻塞。
最后，在打release包的时候，因为我们会混淆，要特别设置不要混淆WebChromeClient子类里面的openFileChooser方法，由于不是继承的方法，所以默认会被混淆，然后就无法选择文件了。
就这样吧。
原文地址：http://blog.isming.me/2015/12/21/android-webview-upload-file/

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