SCRIPTING FROM THE GROUND UP in Objective-C

Print QR Code 2d barcode in Objective-C SCRIPTING FROM THE GROUND UP

Getting the values of an object s properties using the command get properties is a bit different. Not only do you get the list of property names, but you also get the value of all or most properties for a specific object. Let s try to get the properties for a single file in the Finder. You will first need to identify the file whose properties you want to get. To do that, you will use the choose folder command, which returns an alias value identifying the folder. After putting that value in a variable, you will ask the Finder to get you the properties of that folder. Create a new script window, and enter the four lines shown in Figure 2-15.

Figure 2-15. The script and the resulting properties of a chosen folder The result of the script is a record that contains about 30 properties associated with the folder class and their values that apply to the actual folder you chose. Although the get properties of folder the_alias statement seems like its own little command, it is not. The command is actually the verb get, and properties is a reference to the property named properties. Some object properties return a number, such as size, and some return text, such as name. The properties property returns a record that includes most of the other properties. Looking at the folder properties you got (Figure 2-15), you can see that each property label/property value pair is separated by commas and that the value is separated from the label by a colon. Here is part of it: {name:"first book script", index:3, displayed name:"first book script" name extension:"", extension hidden:false, ... You can easily tell that the value of the property name is "first book script", the index is 3, extension hidden is false, and so on.

The properties property exists in most objects in many applications, so it s almost a sure bet that you will get the results you want if you try it. All you have to do is make sure you have a valid object reference (see the How to Talk to Objects So They Listen section later in this chapter).

As you look at a class s properties in the dictionary, some properties will have r/o written next to them. These properties are read-only, which means you can ask to see their value, but you can t change it. Although initially it appears to be a questionable restriction, some properties were simply not meant to be tampered with or are naturally unchangeable. Take the application Address Book, for example. When you create a new person entry, that person automatically gets a creation date value assigned to it. Although being able to use AppleScript to get the creation date of a person is nice, it would not make any sense if you could change that date; it would no longer be the creation date, but just any date. If you try to change the value of a read-only property, as in the script shown in Figure 2-16, you will get an error, as shown in Figure 2-17.

As you already know, in order to have your commands obeyed, you must address the recipient correctly. In AppleScript, you have many ways to address objects that will make them eligible to receive and obey your script s commands. These ways of pointing to an object are called reference forms. Mastering reference forms is crucial to the success of your script. If you can t point to the right object using the appropriate reference form, your script will not function as expected, if at all. The coming sections will help you understand reference forms and how to use them. Let s return for a minute to the dean at the made-up school. The dean s job today is to assign the extracurricular duties to students. Before naming the duties that need to be carried out (the commands), he needs to identify the students who will perform the tasks. Based on what you know so far, he can give tasks to each student individually: tell the student in seat 4 of row 8 of Mr. Popokovich s class that his duty is dishwashing at the cafeteria. Or, in other words: the duty of the student of seat 4 of row 8 of Mr. Popokovich s class is dishwashing. Although this is all good, the poor dean will realize soon enough that in order to name all the students and duties for the day, he will need to spend the entire afternoon assigning duties! He needs a better system.