MQL4: How to Get the Type of an Object?

Introduction to Object Types in MQL4

In MQL4, graphical objects play a crucial role in visualizing data and automating trading strategies. Understanding the type of an object is essential for manipulating it correctly and building robust Expert Advisors (EAs) or custom indicators.

What are Objects in MQL4?

Objects in MQL4 are graphical elements that can be drawn on a chart, such as trendlines, rectangles, text labels, arrows, and more. These objects are identified by a unique name and have various properties that define their appearance and behavior.

Importance of Determining Object Types

Knowing the type of an object allows you to apply the correct functions and properties to it. For example, a trendline object has different properties compared to a rectangle object. Attempting to set a property that doesn’t exist for a particular object type will lead to errors. Efficient object handling depends on accurate type identification.

Methods for Identifying Object Types

Several methods can be used to determine the type of an object in MQL4. These methods leverage built-in functions and properties to provide information about the object’s nature.

Using ObjectCreate() and ObjectSetInteger() for Type Identification

While not directly providing the type, the ObjectCreate() function, along with subsequent calls to ObjectSetInteger() with OBJPROP_TYPE, indirectly defines the object type. The initial creation determines the type, which can be implicitly known from your code. However, if dealing with objects created dynamically or by other EAs, further verification is needed.

Utilizing OBJPROP_TYPE Property

The OBJPROP_TYPE property is the most direct way to get an object’s type. This property returns an integer value representing the object’s type. The values correspond to predefined constants like OBJ_TREND, OBJ_RECTANGLE, OBJ_TEXT, etc.

Comparing Object Properties to Determine Type

In some cases, you might not have direct access to the OBJPROP_TYPE. An alternative is to check for the existence of specific properties. For instance, a trendline will have properties related to its ray extension, while a rectangle will have anchor points for its corners. This method is less reliable but can be helpful in certain situations.

Practical Examples and Code Snippets

Here are some practical examples demonstrating how to identify object types in MQL4 using the OBJPROP_TYPE property.

Example 1: Identifying a Trendline Object

string objectName = "MyTrendline";
int objectType = ObjectGetInteger(0, objectName, OBJPROP_TYPE);

if (objectType == OBJ_TREND)
  Print("Object '" + objectName + "' is a Trendline.");
else
  Print("Object '" + objectName + "' is not a Trendline.");

Example 2: Determining if an Object is a Rectangle

string objectName = "MyRectangle";
int objectType = ObjectGetInteger(0, objectName, OBJPROP_TYPE);

if (objectType == OBJ_RECTANGLE)
  Print("Object '" + objectName + "' is a Rectangle.");
else
  Print("Object '" + objectName + "' is not a Rectangle.");

Example 3: Handling Different Object Types in a Loop

int totalObjects = ObjectsTotal(0, -1, -1);

for (int i = 0; i < totalObjects; i++)
{
  string objectName = ObjectName(0, i, -1, -1);
  int objectType = ObjectGetInteger(0, objectName, OBJPROP_TYPE);

  switch (objectType)
  {
    case OBJ_TREND:
      Print("Object '" + objectName + "' is a Trendline.");
      // Specific trendline handling logic here
      break;
    case OBJ_RECTANGLE:
      Print("Object '" + objectName + "' is a Rectangle.");
      // Specific rectangle handling logic here
      break;
    case OBJ_TEXT:
      Print("Object '" + objectName + "' is a Text Label.");
      // Specific text label handling logic here
      break;
    default:
      Print("Object '" + objectName + "' is an unknown object type.");
      break;
  }
}

Advanced Techniques and Considerations

Dealing with Custom Objects and Indicators

When working with custom indicators that create their own graphical objects, ensure you correctly manage the object types. Document the object types created by your custom indicators and provide methods for other EAs or indicators to identify them correctly. Consider using naming conventions or object properties to differentiate custom objects.

Error Handling and Type Checking Best Practices

Always implement error handling when working with objects. Check if the object exists before attempting to retrieve its type or properties. Use ObjectFind() to verify the object’s existence. Validate the returned object type to prevent unexpected behavior. If ObjectGetInteger() fails it returns an error, so check GetLastError() accordingly.

Conclusion

Summary of Object Type Identification in MQL4

Identifying the type of an object in MQL4 is fundamental for efficient object manipulation and error-free coding. The OBJPROP_TYPE property provides the most direct and reliable way to determine an object’s type. Understanding different object types and handling them correctly is critical for creating robust and versatile EAs and custom indicators.

Further Resources and Learning

• MQL4 Reference: Explore the official MQL4 documentation for detailed information on object functions and properties.
• MQL4 Community Forums: Engage with other MQL4 developers to learn from their experiences and solutions.