FileProvider在GetUriForFile上抛出异常

Question

我在FileProviders上的android开发人员参考上遵循了示例代码,但它不起作用.

我files/exports/在我的Manifest中的文件提供程序定义中设置了路径,并且引用的文件确实存在于该路径中.

在我的清单中:

<provider android:name="android.support.v4.content.FileProvider" android:authorities="com.company.app.fileprovider" android:exported="false" android:grantUriPermissions="true">
    <meta-data android:name="android.support.FILE_PROVIDER_PATHS" android:resource="@xml/file_paths" />
</provider>

并在 xml/file_paths.xml

<?xml version="1.0" encoding="UTF-8" ?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <files-path name="exports" path="exports/"/>
</paths>

然后我尝试使用以下代码获取content-uri:

Java.IO.File exportFile = 
    new Java.IO.File ("/data/data/com.company.app/files/exports/file.pdf"); 
Android.Net.Uri exportUri = 
    Android.Support.V4.Content.FileProvider.GetUriForFile (this, "com.company.app.fileprovider", exportFile);

但是我收到此错误:

Exception of type 'Java.Lang.NullPointerException' was thrown.
  at Android.Runtime.JNIEnv.CallStaticObjectMethod (IntPtr jclass, IntPtr jmethod, Android.Runtime.JValue[] parms) [0x00064] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.10.2-branch/4b53fbd0/source/monodroid/src/Mono.Android/src/Runtime/JNIEnv.g.cs:1160 
  at Android.Support.V4.Content.FileProvider.GetUriForFile (Android.Content.Context context, System.String authority, Java.IO.File file) [0x00000] in <filename unknown>:0 
  at com.company.App.ImageAndSubtitle.cloudStorageDidDownloadFile (System.Object sender, com.company.App.CloudStorageEventArgs args) [0x001f7] in /app_path/Screens/ImageAndSubtitle.cs:187 
  --- End of managed exception stack trace ---
java.lang.NullPointerException
    at android.support.v4.content.FileProvider.parsePathStrategy(FileProvider.java:243)
    at android.support.v4.content.FileProvider.getPathStrategy(FileProvider.java:217)
    at android.support.v4.content.FileProvider.getUriForFile(FileProvider.java:130)
    at mono.java.lang.RunnableImplementor.n_run(Native Method)
    at mono.java.lang.RunnableImplementor.run(RunnableImplementor.java:29)
    at android.os.Handler.handleCallback(Handler.java:615)
    at android.os.Handler.dispatchMessage(Handler.java:92)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:4838)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:511)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:875)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:642)
    at dalvik.system.NativeStart.main(Native Method)

更新

从Android源代码我可以追捕到目前为止,我现在知道这个命令android.support.v4.content.FileProvider.parsePathStrategy(FileProvider.java:243)将失败并返回null:

final ProviderInfo info = context.getPackageManager().resolveContentProvider(authority, PackageManager.GET_META_DATA);

但我不知道为什么......

Answer 1

我终于找到了关于如何在https://github.com/commonsguy/cw-omnibus/tree/master/ContentProvider上创建ContentProviders和FileProviders的良好示例代码

我的代码中的实际错误是在Manifest文件中我有provider标签之外的application标签,但它必须在里面.清单必须如下所示:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" android:versionCode="1" android:versionName="1.0" package="com.company.app">
<uses-sdk android:minSdkVersion="13" />

<permission
    android:name="com.company.app.fileprovider.READ"
    android:description="@string/perm_read"
    android:label="@string/perm_read_label"/>
<uses-permission android:name="com.company.app.fileprovider.READ"/>

<application android:label="MyApp">

    <provider 
    android:name="android.support.v4.content.FileProvider" 
    android:authorities="com.company.app.fileprovider" 
    android:exported="false" 
    android:grantUriPermissions="true"
    android:readPermission="com.company.app.fileprovider.READ">
                <meta-data 
                android:name="android.support.FILE_PROVIDER_PATHS" 
                android:resource="@xml/file_paths" />
    </provider>

</application>
<uses-permission android:name="android.permission.INTERNET" />

</manifest>

Answer 2

在尝试设置FileProvider以获取设备上的PDF文件并能够通过电子邮件发送时,我也遇到了这个例外.阅读那里的不同答案 - 手动设置FileProvider似乎有点复杂(至少第一次).

最后,对我来说有用的是将此示例中的组件复制到一个空的新项目中:https: //github.com/IanDarwin/Android-Cookbook-Examples/tree/master/PdfShare

一旦我看到它在独立工作,那么我就可以将更改引入我的实际项目中.

具体来说,这是要复制的文件:

1. AndroidManifest.xml - 所有棘手的FileProvider配置

• https://github.com/IanDarwin/Android-Cookbook-Examples/blob/master/PdfShare/AndroidManifest.xml

2. file_paths.xml - 这是一个很小但很重要的组件.看看那里有各种各样的答案,但是只有这个项目才能为我设置工作

• https://github.com/IanDarwin/Android-Cookbook-Examples/blob/master/PdfShare/res/xml/file_paths.xml

3. MainActivity.java - 相应的Java设置,用于清单中配置的内容; 当然不要忘记关联的布局文件

• https://github.com/IanDarwin/Android-Cookbook-Examples/blob/master/PdfShare/src/main/java/com/example/pdfshare/MainActivity.java