Display Properties of Columns and Fields
To change the display properties of columns and fields you need to login as System Administrator. All settings are made in the windows Window, Tab & Field and Table and Column.
Read Only (Logic)
To make a field readonly open the window Window, Tab & Field and navigate to the field (in the Field tab). Check the Read Only checkbox to make the field readonly. This will overwrite the corresponding setting in the Table and Column window.
To make the readonly state dependent on other conditions (like the state of other fields) open the corresponding column in the Table and Column window. In the Read Only Logic textfield enter a condition like @MyYesNoColumn@=Y. If the condition is met (the MyYesNoColumn checkbox is checked) the field will be readonly.
To make a field visible the Displayed checkbox in the window Window, Tab & Field has to be checked. To make the visibility dependent on other conditions use the Display Logic field in the same window. In ADempiere the display logic is used to display different sets of fields depending on the actual document type, e.g. @OrderType@='SO' (look at the Sales Order window / Order tab for an example). Display Logic is evaluated left to right, no precedence on operators, no parenthesis supported.
To make a field mandatory open the window Table and Column and check the Mandatory checkbox. Sometimes it is usefull to make a field mandatory only if certain conditions are met. To make the mandatory state dependent on other conditions use the Mandatory Logic field in the same window. An example is an error description field that has to be filled only if an error is detected (but then it is mandatory to give a description). The mandatory logic for the error description textfield would be something like '@IsError@=Y'.