java - FileProvider 在空对象引用上导致 XmlResourceParser 和 ProviderInfo.loadXmlMetaData 崩溃

Question

我对 java 和 android studio 很陌生。我尝试在 android 10 API 29 上下载 pdf 文件后打开它。当从 webview 链接单击文件链接时，它可以正常下载，但无法打开，并且应用程序因 logcat 中的这些错误而崩溃。我有一种感觉，我的代码完全搞砸了，因为试图让它工作有点让人不知所措。

这是 logcat 中的错误

Process: com.principalhomerepair.phrAdmin, PID: 20508
    java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.XmlResourceParser android.content.pm.ProviderInfo.loadXmlMetaData(android.content.pm.PackageManager, java.lang.String)' on a null object reference
        at androidx.core.content.FileProvider.parsePathStrategy(FileProvider.java:605)
        at androidx.core.content.FileProvider.getPathStrategy(FileProvider.java:579)
        at androidx.core.content.FileProvider.getUriForFile(FileProvider.java:417)
        at com.principalhomerepair.phrAdmin.MainActivity$6.onDownloadStart(MainActivity.java:358)
        at ic.a(PG:548)
        at An.handleMessage(PG:25)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

这是我的 MainActivity.java

public void onDownloadStart(String url, String userAgent, String contentDisposition, String mimeType, long contentLength) {
    if (!check_permission(2)) {
        ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE, Manifest.permission.READ_EXTERNAL_STORAGE}, file_perm);
    } else {
        DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));

        //Get the name of the file being downloaded from the url
        String fileName = url.substring(url.lastIndexOf("/") + 1);

        request.setMimeType(mimeType);
        String cookies = CookieManager.getInstance().getCookie(url);
        request.addRequestHeader("cookie", cookies);
        request.addRequestHeader("User-Agent", userAgent);
        request.setDescription(getString(R.string.dl_downloading));
        request.setTitle(URLUtil.guessFileName(url, contentDisposition, mimeType));
        request.allowScanningByMediaScanner();
        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
        request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, URLUtil.guessFileName(url, contentDisposition, mimeType));
        DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
        assert dm != null;
        dm.enqueue(request);
        Toast.makeText(getApplicationContext(), getString(R.string.dl_downloading2) + ": " + fileName, Toast.LENGTH_LONG).show();

        //If the file link contains a pdf open it after downloading
        if(mimeType.contains("application/pdf")){
            File pdfFile = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS) + fileName);;

            MimeTypeMap mime = MimeTypeMap.getSingleton();
            String fileExt = pdfFile.getName().substring(pdfFile.getName().lastIndexOf(".") + 1);
            String type = mime.getMimeTypeFromExtension(fileExt);

            Intent openPdf_Intent = new Intent();
            openPdf_Intent.setAction(Intent.ACTION_VIEW);
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
                openPdf_Intent.setFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
                Uri contentUri = FileProvider.getUriForFile(MainActivity.this, "com.your.package.fileProvider", pdfFile);
                openPdf_Intent.setDataAndType(contentUri, type);
            } else {
                openPdf_Intent.setDataAndType(Uri.fromFile(pdfFile), type);
            }

            startActivity(openPdf_Intent);

            Toast.makeText(getApplicationContext(), "Viewing PDF File: " + fileName, Toast.LENGTH_SHORT).show();
        }
    }
}

文件路径.xml

<?xml version ="1.0" encoding ="utf-8"?>
<paths>
<external-path name="Download" path="Download"/>
</paths>

AnodroidManifest.xml

<provider
    android:name="androidx.core.content.FileProvider"
    android:authorities="${applicationId}.provider"
    android:exported="false"
    android:grantUriPermissions="true"
    tools:replace="android:authorities">
    <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/file_paths" />
</provider>

更新了 MainActivity.java

        public void onDownloadStart(String url, String userAgent, String contentDisposition, String mimeType, long contentLength) {


            if (!check_permission(2)) {
                ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE, Manifest.permission.READ_EXTERNAL_STORAGE}, file_perm);
            } else {
                DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));

                //Get the name of the file being downloaded from the url
                String fileName = url.substring(url.lastIndexOf("/") + 1);

                request.setMimeType(mimeType);
                String cookies = CookieManager.getInstance().getCookie(url);
                request.addRequestHeader("cookie", cookies);
                request.addRequestHeader("User-Agent", userAgent);
                request.setDescription(getString(R.string.dl_downloading));
                request.setTitle(URLUtil.guessFileName(url, contentDisposition, mimeType));
                request.allowScanningByMediaScanner();
                request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
                request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, URLUtil.guessFileName(url, contentDisposition, mimeType));
                DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
                assert dm != null;
                dm.enqueue(request);
                Toast.makeText(getApplicationContext(), getString(R.string.dl_downloading2) + ": " + fileName, Toast.LENGTH_LONG).show();

                //If the file link contains a pdf open it after downloading
                if(mimeType.contains("application/pdf")){

                    //Grab the file from the internal storage
                    File pdfFile = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS) + "/" + fileName);

                    MimeTypeMap mime = MimeTypeMap.getSingleton();
                    String fileExt = pdfFile.getName().substring(pdfFile.getName().lastIndexOf(".") + 1);
                    String type = mime.getMimeTypeFromExtension(fileExt);

                    Intent openPdf_Intent = new Intent("com.adobe.reader");
                    openPdf_Intent.setAction(Intent.ACTION_VIEW);
                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
                        openPdf_Intent.setFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
                        Uri contentUri = FileProvider.getUriForFile(MainActivity.this, BuildConfig.APPLICATION_ID + ".provider",pdfFile);

                        openPdf_Intent.setDataAndType(contentUri, type);
                    } else {
                        openPdf_Intent.setDataAndType(Uri.fromFile(pdfFile), type);
                    }
                    //startActivityForResult(intent, ACTIVITY_VIEW_ATTACHMENT);
                    startActivity(openPdf_Intent);

                    Toast.makeText(getApplicationContext(), "Viewing PDF File: " + fileName, Toast.LENGTH_SHORT).show();
                }
            }

        }
    });

应用程序不再崩溃，但不会在 pdf 查看器中打开文件。 Android 设备显示转至 pdf 查看器一瞬间，然后返回有问题的应用程序，仅此而已。它不显示文件

Answer 1

这一行看起来很可疑:

Uri contentUri = FileProvider.getUriForFile(MainActivity.this, "com.your.package.fileProvider", pdfFile);

可能应该是:

BuildConfig.APPLICATION_ID