下载管理器 Android 权限错误：写入外部存储

Question

我编写了一个 Android 应用程序，使用 DownloadManager 将示例 PDF 文件下载到下载目录。这是代码：

 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_vertretungsplan);
    Button dlbutton = (Button) findViewById(R.id.buttondownload);
    final Context c = this;
    dlbutton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            DownloadManager.Request request = new DownloadManager.Request(Uri.parse(myurl));
            request.setTitle("Vertretungsplan");
            request.setDescription("wird heruntergeladen");
            request.allowScanningByMediaScanner();
            request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
            String filename = URLUtil.guessFileName(myurl, null, MimeTypeMap.getFileExtensionFromUrl(myurl));
            request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, filename);
            DownloadManager manager = (DownloadManager) c.getSystemService(Context.DOWNLOAD_SERVICE);
            manager.enqueue(request);
        }
    });
}

现在，我尝试在我的 Xperia Z3 Android 6.0 上从 Android Studio 调试运行它。当我点击下载按钮时，出现了这个错误：

 E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.example.markwitt.schul_app, PID: 29297
              java.lang.SecurityException: No permission to write to /storage/emulated/0/Download/hrpsampletable.pdf: Neither user 10047 nor current process has android.permission.WRITE_EXTERNAL_STORAGE.
                  at android.os.Parcel.readException(Parcel.java:1627)
                  at android.database.DatabaseUtils.readExceptionFromParcel(DatabaseUtils.java:183)
                  at android.database.DatabaseUtils.readExceptionFromParcel(DatabaseUtils.java:135)
                  at android.content.ContentProviderProxy.insert(ContentProviderNative.java:476)
                  at android.content.ContentResolver.insert(ContentResolver.java:1240)
                  at android.app.DownloadManager.enqueue(DownloadManager.java:946)
                  at com.example.markwitt.schul_app.Vertretungsplan$1.onClick(Vertretungsplan.java:59)
                  at android.view.View.performClick(View.java:5280)
                  at android.view.View$PerformClick.run(View.java:21239)
                  at android.os.Handler.handleCallback(Handler.java:739)
                  at android.os.Handler.dispatchMessage(Handler.java:95)
                  at android.os.Looper.loop(Looper.java:224)
                  at android.app.ActivityThread.main(ActivityThread.java:5526)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

与目标 VM 断开连接，地址：’localhost:8600’，传输：’socket’

（在第三行）它向我显示它对外部存储没有写权限。

但是我的 AndroidManifest 设置正确：

 <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.markwitt.schul_app">
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.INTERNET" />
<application
    android:launchMode="singleTop"
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">

    <activity android:name=".Stundenplan">

        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name=".Vertretungsplan"></activity>
</application>

我需要做什么？

原文由 Mark Witt 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

您收到此错误是因为您的应用在 Android 6.0（API 级别 23）中运行。从 API 级别 >= 23 开始，您将需要在运行时检查权限。您的代码适用于 23 级以下。因此，请先检查您的用户是否已授予使用存储的权限：

 if (checkSelfPermission(android.Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) {
    Log.e("Permission error","You have permission");
    return true;
}

如果没有则提示请求：

 ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_CODE);

总的来说是这样的：

 public  boolean haveStoragePermission() {
    if (Build.VERSION.SDK_INT >= 23) {
        if (checkSelfPermission(android.Manifest.permission.WRITE_EXTERNAL_STORAGE)
                == PackageManager.PERMISSION_GRANTED) {
            Log.e("Permission error","You have permission");
            return true;
        } else {

            Log.e("Permission error","You have asked for permission");
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
            return false;
        }
    }
    else { //you dont need to worry about these stuff below api level 23
        Log.e("Permission error","You already have the permission");
        return true;
    }
}

最后一件事 :) 通过回调接收结果：

     @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if(grantResults[0]== PackageManager.PERMISSION_GRANTED){
            //you have the permission now.
            DownloadManager.Request request = new DownloadManager.Request(Uri.parse(myurl));
            request.setTitle("Vertretungsplan");
            request.setDescription("wird heruntergeladen");
            request.allowScanningByMediaScanner();
            request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
            String filename = URLUtil.guessFileName(myurl, null, MimeTypeMap.getFileExtensionFromUrl(myurl));
            request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, filename);
            DownloadManager manager = (DownloadManager) c.getSystemService(Context.DOWNLOAD_SERVICE);
            manager.enqueue(request);
        }
    }

或者，您可以只使用我的自定义类 PermissionCheck 来非常轻松地处理所有这些实现。这是课程：

 import android.Manifest;
import android.app.Activity;
import android.content.Context;
import android.content.pm.PackageManager;
import android.support.v4.app.ActivityCompat;

/**
 * Created by Tushar on 6/30/2017.
 */

public class PermissionCheck{
    public static boolean readAndWriteExternalStorage(Context context){
        if(ActivityCompat.checkSelfPermission(context, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED || ActivityCompat.checkSelfPermission(context, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED){
            ActivityCompat.requestPermissions((Activity) context, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE, Manifest.permission.READ_EXTERNAL_STORAGE}, 1);
            return false;
        }else{
            return true;
        }

    }

    public static boolean audioRecord(Context context){
        if(ActivityCompat.checkSelfPermission(context, Manifest.permission.RECORD_AUDIO) != PackageManager.PERMISSION_GRANTED ){
            ActivityCompat.requestPermissions((Activity) context, new String[]{Manifest.permission.RECORD_AUDIO}, 2);
            return false;
        }else{
            return true;
        }

    }

    public static boolean readAndWriteContacts(Context context){
        if(ActivityCompat.checkSelfPermission(context, Manifest.permission.READ_CONTACTS) != PackageManager.PERMISSION_GRANTED || ActivityCompat.checkSelfPermission(context, Manifest.permission.WRITE_CONTACTS) != PackageManager.PERMISSION_GRANTED){
            ActivityCompat.requestPermissions((Activity) context, new String[]{Manifest.permission.READ_CONTACTS, Manifest.permission.WRITE_CONTACTS}, 3);
            return false;
        }else{
            return true;
        }

    }

    public static boolean vibrate(Context context){
        if(ActivityCompat.checkSelfPermission(context, Manifest.permission.VIBRATE) != PackageManager.PERMISSION_GRANTED){
            ActivityCompat.requestPermissions((Activity) context, new String[]{Manifest.permission.VIBRATE}, 4);
            return false;
        }else{
            return true;
        }

    }

    public static boolean sendSms(Context context){
        if(ActivityCompat.checkSelfPermission(context, Manifest.permission.SEND_SMS) != PackageManager.PERMISSION_GRANTED){
            ActivityCompat.requestPermissions((Activity) context, new String[]{Manifest.permission.SEND_SMS}, 5);
            return false;
        }else{
            return true;
        }

    }

    //Just like this you can implement rest of the permissions.
}

用法：

 if(PermissionCheck.readAndWriteExternalStorage(context)){
    //Your read write code.
}

if(PermissionCheck.sendSms(context)){
    //Your sms sending code.
}

**请注意，这些方法调用将自动请求权限，并且您的 onRequestPermissionsResult 将被触发。 :)

原文由 Tushar Monirul 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 2

不需要做这一切。只需将以下代码粘贴到您的 onCreate() 函数上：

 private static int REQUEST_CODE=1;

ActivityCompat.requestPermissions(this, new String[]{
    Manifest.permission.WRITE_EXTERNAL_STORAGE
}, REQUEST_CODE);

原文由 user9868015 发布，翻译遵循 CC BY-SA 4.0 许可协议