在Android设备上获取已安装应用程序的详细信息..无法获取设备上安装的每个应用程序所需的权限？

Question

我的代码获取权限（已安装的应用程序所需）和其他 Android设备上安装的应用程序的详细信息，但它无法正常工作：

private void populateWithInitialApps() {
       /* StringBuffer appNameAndPermissions = new StringBuffer();
        String[] requestedPermissions =  new String[]{};*/
        //  List<ApplicationInfo> appList = getPackageManager().getInstalledApplications(0);
     // String name =  pm.getApplicationLabel(appList.get(0)).toString();
            //AppItem appItem = new AppItem(appList.get(0).packageName.toString(), appList.get(0).packageName.toString());
        String requestedPermissions1 ;
        for (int i = 0; i < noOfApps; i++) {
                StringBuffer appNameAndPermissions = new StringBuffer();
              String per=  appList.get(0).permission;
                String[] requestedPermissions= new String[]{};
              requestedPermissions1 ="" ;
                try {
                    PackageInfo packageInfo = pm.getPackageInfo(appList.get(i).packageName, PackageManager.GET_PERMISSIONS);
                     ; ;/*packageInfo.requestedPermissions;*/
                  //  if (requestedPermission1s != null) {
                 //   requestedPermissions =  new String[]{};
                       // int j = 0 ;
                    requestedPermissions = packageInfo.requestedPermissions;
                   Log.v("lentth",String.valueOf(requestedPermissions.length));
                    for (int j = 0; j < requestedPermissions.length; j++) {

                        //            appNameAndPermissions=new StringBuffer();
                            Log.d("test", requestedPermissions[j]);
                            appNameAndPermissions.append(requestedPermissions[j] + "\n");


                        }
                /*    while (j<requestedPermissions.length)
                    {
                        Log.d("test", requestedPermissions[j]);
                        requestedPermissions1.concat("  "+requestedPermissions[j]);
                        j++ ;
                    }*/
                    //}
                }
                catch (PackageManager.NameNotFoundException e)
                {

                }

                itemList.add( new AppItem(appList.get(i).packageName.toString(),requestedPermissions1,String.valueOf(appList.get(0).targetSdkVersion),
                        pm.getApplicationLabel(appList.get(i)).toString()));

            }

    }

返回以下错误：

  

requestPermission.length
  java.lang.NullPointerException：尝试获取null数组的长度