apply_joint_force: Simplified using ComponentDefault (gazebosim#2630)

Signed-off-by: Martin Pecka <peci1@seznam.cz>
Co-authored-by: Addisu Z. Taddese <addisu@openrobotics.org>

Author: peci1

src/systems/apply_joint_force/ApplyJointForce.cc

@@ -156,23 +156,14 @@ void ApplyJointForce::PreUpdate(const UpdateInfo &_info,
 
   // Update joint force
   //! [jointForceComponent]
-  auto force = _ecm.Component<components::JointForceCmd>(
-      this->dataPtr->jointEntity);
+  auto force = _ecm.ComponentDefault<components::JointForceCmd>(
+      this->dataPtr->jointEntity, {0.0});
   //! [jointForceComponent]
 
   std::lock_guard<std::mutex> lock(this->dataPtr->jointForceCmdMutex);
 
   //! [modifyComponent]
-  if (force == nullptr)
-  {
-    _ecm.CreateComponent(
-        this->dataPtr->jointEntity,
-        components::JointForceCmd({this->dataPtr->jointForceCmd}));
-  }
-  else
-  {
-    force->Data()[0] += this->dataPtr->jointForceCmd;
-  }
+  force->Data()[0] += this->dataPtr->jointForceCmd;
   //! [modifyComponent]
 }
 

tutorials/component_jointforcecmd.md

@@ -6,12 +6,12 @@ This component allows us to set the force command on a joint.
 
 Programmatic usage of this component can be found in the source code for
 systems and integration tests, such as the
-[joint integration test](https://github.com/gazebosim/gz-sim/blob/gz-sim8/test/integration/joint.cc),
+[joint integration test](https://github.com/gazebosim/gz-sim/blob/gz-sim9/test/integration/joint.cc),
 the \ref gz::sim::systems::ApplyJointForce system
-([source code](https://github.com/gazebosim/gz-sim/tree/gz-sim8/src/systems/apply_joint_force)),
+([source code](https://github.com/gazebosim/gz-sim/tree/gz-sim9/src/systems/apply_joint_force)),
 and others.
 
-The corresponding world SDF is [`apply_joint_force.sdf`](https://github.com/gazebosim/gz-sim/blob/gz-sim8/examples/worlds/apply_joint_force.sdf), which you can look at in Gazebo:
+The corresponding world SDF is [`apply_joint_force.sdf`](https://github.com/gazebosim/gz-sim/blob/gz-sim9/examples/worlds/apply_joint_force.sdf), which you can look at in Gazebo:
 
 ```bash
 gz sim apply_joint_force.sdf
@@ -56,11 +56,13 @@ In this case, we use the joint entity found above to look for and modify its
 `JointForceCmd` component.
 This will apply a force command to the joint.
 
-In `PreUpdate()`, look for the component:
+In `PreUpdate()`, look for the component. If it does not exist yet, create it,
+setting its default value to `{0.0}` (which means, in this particular case,
+a 1-element `std::vector<double>` with value 0.0 in its only element):
 
 \snippet src/systems/apply_joint_force/ApplyJointForce.cc jointForceComponent
 
-Create it if it does not exist yet, and modify it:
+Now modify the value stored in the component:
 
 \snippet src/systems/apply_joint_force/ApplyJointForce.cc modifyComponent