nullreferenceexception

问题 I want to add a Back button in a toolbar that I created because I deleted the default one to have the material design effect with some tabs, but every time I add the code to make that button appear, Android gives an exception saying this: E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.juan.sdfnsdfnskdfnskdfmsfd, PID: 13348 java.lang.NullPointerException: Attempt to invoke virtual method 'int android.support.v4.widget.DrawerLayout.getDrawerLockMode(int)' on a null object

问题 I have built a custom SVG button so that I can have a Xamarin Forms button with text and an SVG image. I have had it working well and then I migrated my project to .NET Standard 2.0. Now, when changing the text on the control I get a Null Reference Exception inside the Xamarin Forms Framework's StackLayout's LayoutChildIntoBoundingRegion method on a ListDictionaryInternal. Here is the control. It is pretty simple. using System.Windows.Input; using FFImageLoading.Svg.Forms; using Core

问题 I have been playing around with linking XML files to dropdown lists and gridviews. I have managed to populate one dropdown list from the XML document and then a gridview to another but when try to add a where clause, I get a null reference exception and not sure why. How can I resolve this? XDocument xmlDoc = XDocument.Load(Server.MapPath("XMLFile.xml")); var q = from c in xmlDoc.Descendants("Images") where c.Attribute("PropertyId").Value == DropDownList1.SelectedValue.ToString() select new {

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 I have a GridView and, using a fairly common method, I'm using a FooterRow and TemplateFields to provide the missing insert ability. So far so good. The footer contains a TemplateField with a LinkButton to provide the postback that does the insertion. In the handler for the LinkButton's click, the Insert() method is called on the ObjectDataSource that the GridView is bound to. The ObjectDataSource's insert parameters are populated in the handler for its Inserting event. The code for all of

问题 This question is somewhat related to my previous one answer to which helped me to find the reason why this simple iteration thru SqlDataReader: m_aFullIDList = New Generic.List(Of Integer) While i_oDataReader.Read m_aFullIDList.Add(i_oDataReader.GetInt32(0)) End While m_iTotalNumberOfRecords = m_aFullIDList.Count does not return all the records. Turned out when Generic.List changes its Capacity to accommodate more elements (e.g from 2^19 to next one 2^20) at this point SqlDataReader simple

问题 It was a beautiful day, and I came into work and Sitecore randomly gives me this: [NullReferenceException: Object reference not set to an instance of an object.] Sitecore.UIUtil.GetBrowserClassString() +491 Sitecore.sitecore.login.LoginPage.AddBrowserAttributes() +134 Sitecore.sitecore.login.LoginPage.OnPreRender(EventArgs e) +434 System.Web.UI.Control.PreRenderRecursiveInternal() +112 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean

问题 I am trying to make so when I press a row on my UITableView, it will send some data to another UIViewController and make a seque. However when testing it out, it gives me: System.NullReferenceException has been thrown Object reference not set to an instance of an object The error seems to show here: viewController.NavigationController.PushViewController (detail, true); Here is my "RowSelected" public override void RowSelected (UITableView tableView, NSIndexPath indexPath) { Console.WriteLine

问题 I'm trying to use the rng from java when I click a button but each time I click it the program crashes and gives me the following error: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.Random.nextInt(int)' on a null object reference at me.test.first.MainActivity.onGenPress(MainActivity.java:25) Button Press Method public void onGenPress(View v){ TextView tv = (TextView) findViewById(R.string.copper); int number = 1 + dice.nextInt(rollProgressMA); co

问题 I created a clean WindowsFormsApplication solution, added a ToolStrip to the main form, and placed one button on it. I've added also an OpenFileDialog , so that the Click event of the ToolStripButton looks like the following: private void toolStripButton1_Click(object sender, EventArgs e) { openFileDialog1.ShowDialog(); } I didn't change any other properties or events. The funny thing is that when I double-click the ToolStripButton (the second click must be quite fast, before the dialog opens