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问题 This post is a Community Wiki . Edit existing answers to improve this post. It is not currently accepting new answers. I have some code and when it executes, it throws a NullReferenceException , saying: Object reference not set to an instance of an object. What does this mean, and what can I do to fix this error? 回答1: What is the cause? Bottom Line You are trying to use something that is null (or Nothing in VB.NET). This means you either set it to null , or you never set it to anything at all

问题 On android pie i am getting null response for retrofit2 request. Same code is working on all previous android devices. i have added android:usesCleartextTraffic="true" in manifest its fixed the issue of http connection but i am not getting response as expected in all other androided version the response is expected but not in pie. so please help thanks in advance Manifest.xml <application android:allowBackup="false" tools:replace="android:allowBackup" android:icon="@mipmap/cabad_logo_new"

问题 this is an example for something i want to do but the line if let json = try JSONSerialization.jsonObject(with: data) as? [String: String] is false because the return of JSONSerialization.jsonObject is nil func parser(lbl: UILabel){ let postString = "xxx=xxx&xxxx=xxxx==&xxxxx=xxxxx&xxxxxx=xxxxxx&xx=xx" let url = URL(string: "http://xxxxxxxxxx.com/xxxxxx/xxxxx/xxxxxx.php")! var request = URLRequest(url: url) request.httpMethod = "POST" request.httpBody = postString.data(using: .utf8) let task

问题 I have been having this problem for weeks and have not been able to find a solution. When trying to use Eclipse or trying to compile with plain GCC or G++ through a terminal, there are a number of standard functions (plus the "NULL" variable) that are not recognized, including the to_string method. I have attempted to add many different headers to the program in an attempt to find the correct files, but to no avail. I have tried #including <string>, <stdio.h>, <stddef.h>, <cstdlib> , and

问题 In ruby I can do this: 1.9.3-p448 :001 > a = 1 || 2 => 1 1.9.3-p448 :004 > a = nil || 2 => 2 1.9.3-p448 :005 > a = 1 || nil => 1 Is there a similar one-liner in Python? 回答1: Just use the or operator. From the linked page: x or y : if x is false, then y, else x Example: In [1]: 1 or 2 Out[1]: 1 In [2]: None or 2 Out[2]: 2 In [3]: 1 or None Out[3]: 1 回答2: Python's or operator is pretty much the equivalent of Ruby's || -- and None can be used in Python somewhat similarly to how nil is in Ruby.

问题 I am trying to create Union field in Avro schema and send corresponding JSON message with it but to have one of the fields - null . https://avro.apache.org/docs/1.8.2/spec.html#Unions What is example of simplest UNION type (avro schema) with corresponding JSON data? (trying to make example without null/empty data and one with null/empty data). 回答1: Here you have an example. Null enum {"name": "Stephanie", "age": 30, "sex": "female", "myenum": null} Not null enum {"name": "Stephanie", "age":

问题 I'm trying to convert blank cells in a csv file to NULL and upload them in SQL Server table so it shows as NULL rather blank. below code works but they load NULL as a string. Can you please help me to modify the code so it loads NULL in SQL ? reader = csv.reader(f_in) # setup code writer = csv.writer(f_out) row = next(reader) # handle first line (with no replacements) writer.writerow(row) last_row = row # always save the last row of data that we've written variable = None for row in reader: #

问题 Suppose I have a data like this first_name last_name city John Bon Jovi null John Lennon null John Deer null And I want to create aggregating query which will return json which looks like this { "first_name": "John", "city": null } Essentially, the query should check if there's only one distinct value within each column and if it is, put this value to json. All non-null columns are relatively easy to get with a query like this: select case when count(distinct first_name) = 1 then max(first

问题 I want to remove null values from this array. Array( [0] => Array( [fcmToken] => 123 ) [1] => Array( [fcmToken] => ) [2] => Array( [fcmToken] => 789 ) ) Expected Results Array( [0] => Array( [fcmToken] => 123 ) [1] => Array( [fcmToken] => 789 ) ) 回答1: Here we are using foreach to iterate over values and using $value for non-empty $value["fcmToken"] $result=array(); foreach($array as $key => $value) { if(!empty($value["fcmToken"])) { $result[]=$value; } } print_r($result); Output: Array ( [0]

问题 I have an activity in manifest: <activity android:name="RingdroidSelectActivity" android:label="@string/main_activity_label"> <intent-filter> <action android:name="android.intent.action.GET_CONTENT" /> <category android:name="android.intent.category.DEFAULT" /> <category android:name="android.intent.category.OPENABLE" /> <data android:mimeType="audio/*" /> </intent-filter> </activity> When using the following code to open it: startActivity (new Intent(getApplicationContext(), com.ringdroid