作为序言，我熟悉编码（在高中2年），但对于Android Studio（以及一般的Java）来说，我是一个完整的新手。我一直在为我的问题寻找解决方案，但由于我的经验不足，我不知道如何为我的项目实施解决方案。
简而言之，我需要从一些外部URL下载pdf，将其存储到外部存储中，并使用一些pdf-viewer应用程序显示它。我一直在收到错误：
...
android.os.FileUriExposedException：file：///storage/emulated/0/pdf/Read.pdf通过Intent.getData（）暴露在app之外
...
我一直在使用this source on using an intent to open a pdf-viewer和this source on "File Provider"作为参考。
以下是我到目前为止：
public class Fire extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_fire);
final TextView testButton = findViewById(R.id.testPDF);
// File file = getFilesDir();
testButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(Fire.this, pdfView.class);
startActivity(intent);
}
});
public class pdfView extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_pdf_view);
String extStorageDirectory = Environment.getExternalStorageDirectory().toString();
File folder = new File(extStorageDirectory, "pdf");
folder.mkdir();
File file = new File(folder, "Read.pdf");
try {
file.createNewFile();
} catch (IOException e1) {
e1.printStackTrace();
}
Downloader.DownloadFile(__PDF_URL___, file);
showPdf();
}
public void showPdf()
{
File file = new File(Environment.getExternalStorageDirectory()+"/pdf/Read.pdf");
PackageManager packageManager = getPackageManager();
Intent testIntent = new Intent(Intent.ACTION_VIEW);
testIntent.setType("application/pdf");
List list = packageManager.queryIntentActivities(testIntent, PackageManager.MATCH_DEFAULT_ONLY);
Intent intent = new Intent();
intent.setAction(Intent.ACTION_VIEW);
Uri uri = Uri.fromFile(file);
intent.setDataAndType(uri, "application/pdf");
startActivity(intent);
}
public class Downloader {
public static void DownloadFile(String fileURL, File directory) {
try {
FileOutputStream f = new FileOutputStream(directory);
URL u = new URL(fileURL);
HttpURLConnection c = (HttpURLConnection) u.openConnection();
c.setRequestMethod("GET");
c.setDoOutput(true);
c.connect();
InputStream in = c.getInputStream();
byte[] buffer = new byte[1024];
int len1 = 0;
while ((len1 = in.read(buffer)) > 0) {
f.write(buffer, 0, len1);
}
f.close();
} catch (Exception e) {
e.printStackTrace();
}
}
根据我的研究，似乎我的问题源于我使用URI而不是“文件提供程序”。此外，实现“文件提供者”的解决方案似乎以某种形式使用 Context ，而我对上下文的目的是什么以及如何实现它感到困惑。
如果你没有答案那么好。任何有关如何理解或甚至理解这个概念的信息对我来说都足够了。
答案 0 :(得分：0)
如果你的targetSdkVersion＆gt; = 24，那么我们必须使用FileProvider类来访问特定文件或文件夹，以使其可供其他应用访问。
1）首先在AndroidManifest.xml中的标签下添加一个FileProvider标签，如下所示：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
...
<application
...
<provider
android:name=".GenericFileProvider"
android:authorities="${applicationId}.my.package.name.provider"
android:exported="false"
android:grantUriPermissions="true">
<meta-data
android:name="android.support.FILE_PROVIDER_PATHS"
android:resource="@xml/provider_paths"/>
</provider>
</application>
</manifest>
2）然后在res / xml文件夹中创建provider_paths.xml文件。如果文件夹不存在，则可能需要创建文件夹。
<paths>
<external-path name="external_files" path="."/>
</paths>
3）现在创建PdfDownload.java类文件并粘贴到代码下面：
public class PdfDownload extends Activity {
TextView tv_loading;
Context context;
int downloadedSize = 0, totalsize;
float per = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
isStoragePermissionGranted();
super.onCreate(savedInstanceState);
tv_loading = new TextView(this);
tv_loading.setGravity(Gravity.CENTER);
tv_loading.setTypeface(null, Typeface.BOLD);
setContentView(tv_loading);
downloadAndOpenPDF();
}
public static String getLastBitFromUrl(final String url) {
return url.replaceFirst(".*/([^/?]+).*", "$1");
}
void downloadAndOpenPDF() {
final String download_file_url = getIntent().getStringExtra("url");
new Thread(new Runnable() {
public void run() {
Uri path = Uri.fromFile(downloadFile(download_file_url));
try {
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
Uri uri = FileProvider.getUriForFile(PdfDownload.this, BuildConfig.APPLICATION_ID, downloadFile(download_file_url));
intent.setDataAndType(uri, "application/pdf");
startActivity(intent);
finish();
} catch (ActivityNotFoundException e) {
tv_loading
.setError("PDF Reader application is not installed in your device");
}
}
}).start();
}
File downloadFile(String dwnload_file_path) {
File file = null;
try {
URL url = new URL(dwnload_file_path);
HttpURLConnection urlConnection = (HttpURLConnection) url
.openConnection();
urlConnection.connect();
String test = getLastBitFromUrl(dwnload_file_path);
String dest_file_path = test.replace("%20", "_");
// set the path where we want to save the file
File SDCardRoot = Environment.getExternalStorageDirectory();
// // create a new file, to save the downloaded file
file = new File(SDCardRoot, dest_file_path);
if (file.exists()) {
return file;
}
FileOutputStream fileOutput = new FileOutputStream(file);
// Stream used for reading the data from the internet
InputStream inputStream = urlConnection.getInputStream();
// this is the total size of the file which we are
// downloading
totalsize = urlConnection.getContentLength();
setText("Starting PDF download...");
// create a buffer...
byte[] buffer = new byte[1024 * 1024];
int bufferLength = 0;
while ((bufferLength = inputStream.read(buffer)) > 0) {
fileOutput.write(buffer, 0, bufferLength);
downloadedSize += bufferLength;
per = ((float) downloadedSize / totalsize) * 100;
if ((totalsize / 1024) <= 1024) {
setText("Total PDF File size : " + (totalsize / 1024)
+ " KB\n\nDownloading PDF " + (int) per + "% complete");
} else {
setText("Total PDF File size : " + (totalsize / 1024) / 1024
+ " MB\n\nDownloading PDF " + (int) per + "% complete");
}
// setText("configuring your book pleease wait a moment");
}
// close the output stream when complete //
fileOutput.close();
// setText("Download Complete. Open PDF Application installed in the device.");
setText("configuaration is completed now your book is ready to read");
} catch (final MalformedURLException e) {
setTextError("Some error occured. Press back and try again.",
Color.RED);
} catch (final IOException e) {
setTextError("Some error occured. Press back and try again.",
Color.RED);
} catch (final Exception e) {
setTextError(
"Failed to download image. Please check your internet connection.",
Color.RED);
}
return file;
}
void setTextError(final String message, final int color) {
runOnUiThread(new Runnable() {
public void run() {
tv_loading.setTextColor(color);
tv_loading.setText(message);
}
});
}
void setText(final String txt) {
runOnUiThread(new Runnable() {
public void run() {
tv_loading.setText(txt);
}
});
}
private static final String TAG = "MyActivity";
public boolean isStoragePermissionGranted() {
if (Build.VERSION.SDK_INT >= 23) {
if (checkSelfPermission(android.Manifest.permission.WRITE_EXTERNAL_STORAGE)
== PackageManager.PERMISSION_GRANTED) {
Log.v(TAG, "Permission is granted");
return true;
} else {
Log.v(TAG, "Permission is revoked");
ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
return false;
}
} else { //permission is automatically granted on sdk<23 upon installation
Log.v(TAG, "Permission is granted");
return true;
}
}
@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
super.onRequestPermissionsResult(requestCode, permissions, grantResults);
if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
Log.v(TAG, "Permission: " + permissions[0] + "was " + grantResults[0]);
}
}
}