cursor | 易学教程

Android--数据持久化之SQLite

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前言　　对于一个应用程序而言，数据持久化是必不可少的，Android程序也不例外。这篇博客将介绍Android中关于SQLite的使用，SQLite是一种嵌入式的数据库引擎，专门适用于资源有限的设备上进行适量的数据存储，而Android就全面支持标准的SQLite数据库。在本片博客中，将说明SQLite数据库的创建以及维护，还有使用SQLite执行CRUD的两种方式，以及SQLite中事务的使用，最后都会使用示例讲解博客中所提到的概念性的内容。 SQLite 　　Android对SQLite数据库，提供了完全的支持，而所有创建的SQLite数据库，仅限于当前应用访问，如果其他应用需要访问，则必须提供的Content Provider的支持，并且SQLite数据库会随着Android应用的卸载而被删除。SQLite是一个嵌入式的数据库引擎，最后是以文件的形式保存数据的。从本质上来看，SQLite的操作方式只是一种更为便捷的文件操作，当应用程序创建或打开一个SQLite数据库时，其实只是打开一个文件准备读写。因为SQLite仅适用于资源有限的小型设备，所以本身就不应该把大量数据存储在设备的SQLite数据库里，SQLite只适合存储一些小型的数据。　　为了使SQLite和其他数据库间的兼容性最大化，SQLite支持对列上类型进行“类型近似”

How to avoid db not close and cursor exception

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问题 02-02 14:31:34.048: WARN/SQLiteCompiledSql(359): Releasing statement in a finalizer. Please ensure that you explicitly call close() on your cursor: SELECT * FROM 02-02 14:31:34.048: WARN/SQLiteCompiledSql(359): android.database.sqlite.DatabaseObjectNotClosedException: Application did not close the cursor or database object that was opened here 02-02 14:31:34.129: ERROR/Database(359): android.database.sqlite.DatabaseObjectNotClosedException: Application did not close the cursor or database

C# cursor highlighting/follower

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问题 How to highlight the system cursor? Like many screen recording applications do. Ideally, I'd like to display a halo around it. Thanks 回答1: For a purely managed solution, the following code will draw an ellipse on the desktop at the current mouse cursor position. Point pt = Cursor.Position; // Get the mouse cursor in screen coordinates using (Graphics g = Graphics.FromHwnd(IntPtr.Zero)) { g.DrawEllipse(Pens.Black, pt.X - 10, pt.Y - 10, 20, 20); } By using a timer you can update the mouse

Cursor Index Out of Bounds Exception

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问题 In attempting to execute a query on my database, I get this exception. However, the documentation states that the method SQLiteDatabase.query(...) returns, "A Cursor object, which is positioned before the first entry," which I interpret to mean that the Cursor is at the start of the rows returned. If I add the Cursor.moveToFirst() before accessing data in the Cursor, I get no exception. What is going on? Do I need to always call "moveToFirst" before trying to get data? The documentation says

SQL 游标

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DECLARE My_Cursor CURSOR --定义游标 FOR (SELECT * FROM dbo.MemberAccount) --查出需要的集合放到游标中 OPEN My_Cursor; --打开游标 FETCH NEXT FROM My_Cursor ; --读取第一行数据 WHILE @@FETCH_STATUS = 0 BEGIN --UPDATE dbo.MemberAccount SET UserName = UserName + 'A' WHERE CURRENT OF My_Cursor; --更新 --DELETE FROM dbo.MemberAccount WHERE CURRENT OF My_Cursor; --删除 FETCH NEXT FROM My_Cursor; --读取下一行数据 END CLOSE My_Cursor; --关闭游标 DEALLOCATE My_Cursor; --释放游标 GO DECLARE @UserId varchar(50) DECLARE My_Cursor CURSOR --定义游标 FOR (SELECT UserId FROM dbo.MemberAccount) --查出需要的集合放到游标中 OPEN My_Cursor; --打开游标 FETCH NEXT FROM My_Cursor INTO

Javascript erase image with cursor

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问题 Is it possible with javascript? I'm trying to implement a scratchcard type thing, and I was wondering if the user could 'scratch it' with his cursor and then javascript would remove/erase the image to show the text below. But i've not been able to find anything (javascript wise) which can erase abit (cursor location) of an image. Does anyone have any suggestions/ideas? Thanks. 回答1: Use html5 canvas element. Checkout this fiddle for an example: http://jsfiddle.net/ArtBIT/WUXDb/1/ 回答2: jQuery

Select running total until specific SUM is reached

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问题 I am trying to select the first n rowid values from the following table variable that will get me as close to a sum(itemcount) of 200,000 without crossing that threshhold. If I was looking at this manually, I would just take the top 3 rows. I do not want to use a cursor unless there is no pure-set-based way. What is a good set-based way to get all of the rowid values "sum while/until" I get to a running total of 200,000? I looked at "running totals" at http://www.1keydata.com/sql/sql-running

SQL Server How to output one table result from multiple results with a WHILE query

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问题 From this answer: Is there a way to loop through a table variable in TSQL without using a cursor? I'm using the method WHILE EXISTS(SELECT * FROM #Temp) The problem is that it's outputting multiple tables, if possible I'd like to output as a single table. Declare @Id int WHILE EXISTS(SELECT * FROM #Temp) Begin Select Top 1 @Id = Id From #Temp --Do some processing here Delete #Temp Where Id = @Id End So right now it outputs this: x y -- -- 1 a x y -- -- 1 b But I'd like it to output this: x y

MySql Cursor - Creating a procedure

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问题 i'm trying to create a cursor for the first time. I have looked at the documentation, i understand the concept, but i can't seem to get it to even be declared... I'm using: MySql 5.1.41 SqlYog as a manager (running locally on a xampp instalation) Even when copy pasting the example found in http://dev.mysql.com/doc/refman/5.1/en/cursors.html CREATE PROCEDURE curdemo() BEGIN DECLARE done INT DEFAULT 0; DECLARE a CHAR(16); DECLARE b,c INT; DECLARE cur1 CURSOR FOR SELECT id,data FROM test.t1;

Debian 9 美化界面

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Debian 桌面美化安装 gnome-tweak-tool aptitude install gnome-tweak-tool 登陆 gnome-look 下载主题包 gnome-look上有很多主题包，这里主要讲解以下几种主题的安装配置方法 GTK3 Themes Icon Themes Gnome Shell Themes Mouse Cursors GTK3 Themes 安装将下载下来的主题包解压，然后复制到/usr/share/themes目录 cp -R DarkRed1 /usr/share/themes/ 打开tweak-tool设置这里以我下载的DarkRed1为例 Gnome Shell Themes 安装这个主题包一般会包含在/usr/share/themes的主题包中，所以将下载下来的包解压到/usr/share/themes 打开tweak-tool设置这里的Shell theme主题默认没有开启，需要先开启Extension选项中的User theses，然后再选择相关的Gnome Shell Themes Icon Themes 安装将下载下来的主题包解压，然后复制到/usr/share/icons目录打开tweak-tool设置,即可看到文件夹图标的改变这里以windows 10 icons为例 Mouse Cursors 安装