README

CROComponents - RemObjects Remotting SDK Component Library

Overview

CROComponents is a Delphi component library that bridges RemObjects Remotting (RPC) with VCL data-aware controls. It enables rapid development of distributed applications by binding UI controls directly to remote service operations.

Technology: Delphi 7, RemObjects Remoting SDK
Created: ~2005 (Delphi 7 era)
Status: This library is posted as a portfolio project only. It is not intended to be used in new projects and is no longer maintained.

License

Creative Commons Attribution 4.0 International (CC BY 4.0) - See LICENSE file for details.

Value Proposition

What Problem Does It Solve?

Building distributed applications with RemObjects Remoting SDK requires significant boilerplate code. Developers must manually:

• Serialize parameters to binary messages
• Handle transport channels and message formatting
• Sync UI controls with remote data
• Manage cursor-like navigation and state

This library provides data-aware controls that work with remote services the same way native Delphi DB controls work with local datasets.

How It Works: A Developer's Perspective

Traditional RemObjects Client (without this library):

// Manual approach - lots of boilerplate
var
  Customer: TCustomer;
begin
  Customer := TCustomer.Create;
  Customer.Name := edtName.Text;
  Customer.Email := edtEmail.Text;
  
  Proxy := TROBinaryProxy.Create(MyService);
  try
    Proxy.SaveCustomer(Customer);
  finally
    Proxy.Free;
  end;
end;

With CROComponents (data-aware approach):

// Configure once at design-time:
// 1. Drop TCROServiceManager on form
// 2. Set OperationForInsert to 'SaveCustomer'
// 3. Bind controls via Expression property:
//    - edtName.Expression = 'Customer.Name'
//    - edtEmail.Expression = 'Customer.Email'
// 4. Add btnSave with action = oaInsert

// At runtime - just call Execute
procedure TForm1.btnSaveClick(Sender: TObject);
begin
  // UI automatically synced to operation parameters
  // Execute sends data to server
  operation1.Execute;
end;

Usage Pattern

1. Setup Service Connection
   • Drop TCROServiceManager on form
   • Configure RORemoteService with server URL/channel
2. Define Operations
   • Add TCROOperation components
   • Set OperationName to remote method
   • Configure parameters via Params collection or expressions
3. Create Data Handles
   • TCROListHandle - represents a list/table of records
   • TCROCursorHandle - represents current record buffer
4. Bind UI Controls
   • Set control's Properties.CursorHandle to point to a cursor handle
   • Set Properties.Expression to map field names
   • Controls auto-sync: UI changes → cursor → remote operation
5. Execute Actions
   • Use TCROOperationExecute actions for Select/Insert/Update/Delete
   • Or call TCROOperation.Execute directly

Comparison with Native Delphi Data Access

Benefits

• Rapid Development: Design-time binding similar to native data controls
• Decoupled UI: Expression-based binding separates UI from data layer
• Consistent UX: Same interaction patterns as native DB-aware controls
• Remote-Ready: Full RPC capabilities without writing serialization code
• State Management: Built-in cursor states (browse/edit/insert/cancel)
• Error Handling: Centralized connection failure events

Architecture

Core RPC Layer (CROOperation.pas)

The foundation implements remote operation handling:

TCROCustomOperation
????????? Manages TRORemoteService connection
????????? Maintains TRODLLibrary (service definition)
????????? Handles TROProxy for communication
????????? Executes remote method calls via binary messaging

TCROOperationParams / TCROOperationParam
????????? Parameter collection for RPC calls
????????? Supports data binding via Expression (e.g., "Form1.Edit1.Text")
????????? Type-safe parameter handling (TRODataType, TRODLParamFlag)
????????? Variant-based value storage with object support

Data Model: Cursor Handles

The library implements a cursor-based data model similar to TDataSet:

TCROHandle (abstract base)
????????? Expression-based property binding
????????? State management (csBrowse, csInsert, csEdit, csCancel)
????????? Auto-edit functionality
????????? Event-driven updates

TCROCursorHandle
????????? Single record buffer (TROComplexType)
????????? Edit/Insert/Delete/Cancel operations
????????? Linked to TCROListHandle for list navigation
????????? Property access via expressions

TCROListHandle  
????????? Collection of TROComplexType records
????????? BOF/EOF navigation (Next/Prior)
????????? Multiple cursor handle support
????????? Expression evaluation for filtering
????????? Index mapping for lookups

Data-Aware Controls

UI components bind to cursor handles:

Each implements ICROCustomControl interface for value synchronization:

• UpdateValue - Refresh UI from cursor data
• UpdateObject - Save UI changes to cursor

Expression Binding System (CROComponentsCommon.pas unit)

Property binding via string expressions:

// Syntax: ComponentName.PropertyName
Expression := 'edtCustomer.Text'  // Binds to edtCustomer's Text property
Expression := 'grdOrders.Data'     // Binds to grid's data source

Key functions:

• GetPropInfoFromExpression - Resolves expression to object/property
• GetNextIdentifier - Parses dot-separated paths
• GetTrueOwner - Finds owning Form/DataModule

Action Framework (CROActions.pas)

Operation execution via Delphi Actions:

TCROCustomAction
????????? Execute conditions (before/after)
????????? Confirmation dialogs
????????? Backward action chains

TCROOperationExecute (Select/Insert/Update/Delete)
????????? Binds to TCROServiceManager
????????? Automatic operation routing
????????? Result handling

Skin System

Optional visual customization:

• TCROSkinControl - Skin update notifications
• TCROSkinProperties - Visual property storage
• TCROSkinImage - Image-based skins
• BitmapToRegion - Transparent image regions

Design Patterns

1. Interface-Based Communication

ICROCustomControl = interface
  ['{F27BD8D2-E4BA-4A40-BF84-E1289E2CD561}']
  procedure UpdateValue;
end;

2. Component Aggregation

TCROCustomEdit = class(TCustomEdit, ICROCustomControl, ICROSkinControl)
  FProperties: TCROProperties;  // Links to cursor handle

3. Expression Parser

Dynamic property binding at design/runtime without code coupling.

4. Lazy Initialization

RORemoteService, RODLLibrary resolved on first access.

Key Implementation Details

RPC Communication Flow

1. Set OperationName on TCROOperation
2. Configure Parameters via Expression or Value
3. Call Execute → serializes to binary via TROBinMessage
4. TROTransportChannel dispatches to server
5. Response deserialized back to parameters

Expression Evaluation

// Runtime binding resolution
procedure TField.SetValue(Value: Variant);
begin
  Instance := nil;
  GetPropInfoFromExpression(Owner, Expression, Instance, PropInfo);
  SetPropValue(Instance, PropInfo^.Name, Value);
end;

State Management

csBrowse ??? csEdit (user types) ??? Post ??? csBrowse
         ??? csInsert (Insert)   ??? Post ??? csBrowse
         ??? csCancel (Escape)  ??? csBrowse

Key Skills Demonstrated

• Component Development: Full VCL component lifecycle, IDE integration
• RPC/Distributed Systems: Binary serialization, transport channels, async operations
• Design Patterns: Interface-based, aggregation, expression evaluation
• Data Binding: Cursor model, property binding, automatic synchronization
• Framework Design: Extensible architecture with skin support
• Delphi Mastery: RTTI, streaming, component editors, design-time registration

Dependencies

• rtl - Delphi runtime
• RemObjects_Core_D7 - RemObjects core
• designide - IDE integration
• vcl - Visual component library
• vcldb - Database VCL