Window State Components

   
Release: 5.6.1
Date: 28 October 2014
Delphi Compatibility:
D1 D2 D3 D4 D5 D6 D7 D2005 D2006 D2007 D2009 D2010 DXE DXE2 DXE3 DXE4
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Overview

The window state components can save and restore a window's size, position and state (minimized, maximized or normal) between program executions. Three components are provided that use different means of storing the information. They are:

TPJWdwState
Records window information in an ini file. The user has control over the ini file name (via the IniFileName property) and the name of the section of the ini file where window information is recorded (using the Section property). Alternatively the ini file and section names can be configured by handling the OnGetIniData event that is triggered immediately before the ini file is read or written.
TPJRegWdwState
Uses the registry to record window information. The registry root key and sub key where the information is stored are controlled by the RootKey(Ex) and SubKey properties, or by handling the OnGetRegData(Ex) event. This event is triggered just before the registry is accessed. Additional application defined data can be read from or written to the registry by handling the OnGettingRegData and OnPuttingRegData events that are triggered after the component reads or writes the registry.
Important Note: You are discouraged from using TPJRegWdwState for programs compiled with Delphi 5 and earlier that may be run on 64 bit Windows, because the component may not be able to access the 64 bit registry view correctly and window state may be lost.
TPJUserWdwState
When using this component the user must handle saving and reading the window state data to or from persistent storage. The component gives the most flexibility of all the components at the expense of placing the storage burden on the user. The component triggers OnReadData and OnSaveData events when it is ready to read or save data.

All components implement the same functionality, controlled by some common properties and events, as follows:

  • The components can automatically restore and save windows when the program starts up and closes down (using the AutoSaveRestore property). If AutoSaveRestore is set to False then the Restore and Save methods must be called from the host application.
  • The Options property can be used to customise the way the window is restored:
    • The components can be instructed to ignore the saved window state – the window is then displayed in the normal state.
    • The window's saved size can be ignored and the default size of the form used instead. This is useful for dialog boxes and fixed size windows.
    • The window can be kept within the current work area of the desktop. If this option is used the window also appears on the correct monitor on multi-monitor systems. If the form containing the window state component is a MDI child form this option keeps the window within the parent form's client area, after allowing for any menu, toolbars or status bar etc.
  • When the form is to be restored in a minimized state it briefly appears on screen in the normal state before being minimized. The MinimizeDelay property controls the delay between the window appearing and being minimized.

TPJWdwState and TPJRegWdwState also support the OnReadWdwState event. Handling this event enables the stored window's state, size and position values to be changed before the window is restored. This event is called after reading the data and before sizing the window. TPJUserWdwState does not expose this event because the user is in charge of reading the data and can modify it in the OnReadData event.

All the components derive from an abstract base class named TPJCustomWdwState. This class provides the core window handling and sizing functionality. It provides abstract methods for accessing the required storage medium. Therefore it is quite straightforward to create further components that use alternative storage systems. All that needs to be provided are methods to read/write the window information along with any additional properties that are required to configure the storage medium.

Note that these components are 64 bit compatible and can be included in VCL packages targetted at 64 bit Windows using Delphi XE2 or later.

Documentation

The components are fully documented online.

There is also an FAQ page hosted on the DelphiDabbler Wiki.

Help File Deprecated
There is a WinHelp help file included in the release that can integrate with the IDE of Delphi 4 to 7 and may only work on Windows XP and earlier.
This file was last updated at release 5.4.1 and is likely to be removed from future releases.

How the components work

The underlying principle used in the code is described in the article How to remember a window's size, state and position.

We can't rely on Delphi's own Width and Height properties for recording window size, since these do not maintain size of the normalised window size when the window is maximized. Instead we have to use the GetWindowPlacement and SetWindowPlacement Windows API calls.

Finding the right time to restore a window on application startup has proved problematic. It is not possible to call the Restore method before the form's window handle has been created. We therefore need to delay any such restoration until the form has been shown. A hook class is used to peek at the Windows messages sent to the parent form. This class forwards relevant messages to the component.

Note: One side effect of this complexity is that you can't create instances of the components at run time using the standard constructor. The code is not initialised properly unless the component is added to a form at design time. A special constructor – CreateStandAlone – has been provided that makes dynamic construction possible.

Demo programs

There are four demo projects included with these components. They are:

  1. StandardDemo.dpr
    Demonstrates how to use the components in the standard way, i.e. dropped on a form from the component palette. This demo uses TPJRegWdwState.
  2. StandAloneDemo.dpr
    Demonstrates how to create and use the components dynamically using the CreateStandAlone constructor. This demo uses TPJWdwState.
  3. UserDemo.dpr
    Demonstrates how to use TPJUserWdwState and load and save data in the OnReadData and OnSaveData events.
  4. MDIDemo.dpr
    Demonstrates the use of TPJWdwState with MDI applications.

Feedback & Queries

If you find any bugs or want to suggest a new feature please report them using the Issue Tracker.

Click the Create Ticket button to create a ticket then complete the form giving as much information as possible. Please note: this issue tracker is shared among all the projects in the DelphiDabbler Code Library, so please make sure you enter wdwstate in the Project edit box. You should also choose Defect in the Type drop down list to report a bug or Enhancement to request a new feature.

If you have created a bug fix or have implemented a new feature please attach a zip file to your ticket that contains your source code.

Should you have any queries about using the components please read the documentation and FAQ.

If you can't find an answer in the documentation then post a message in the discussion group.

Please do not email me or use the contact page to report bugs, ask for new features or to find out how to use the components.
I'm afraid I have very limited time available to support the code library, and can't guarantee I'll find time for personalised advice.