Android特定语言 Xtendroid

Xtendroid是一款Android的领域特定语言，它大大降低样板代码，同时提供巨大的工具支持。Xtendroid利用Xtend transpiler实现，它的特点是能够在Java代码编辑或编译期间具有拓展方法和活动注释（实时编辑代码生成器）功能。活动注释，他特别能够让Xtend比Kotlin或者Groovy语言更加适合DSL的创建。Xtendroid支持的Eclipse和IntelliJ/ Android Studio，其中包括代码完成，调试等。

举例特点

Anonymous inner classes (lambdas)

Android code:

// get button widget, set onclick handler to toast a message

Button myButton = (Button) findViewById(R.id.my_button);

myButton.setOnClickListener(new View.OnClickListener() {

   public void onClick(View v) {

      Toast.makeText(this, "Hello, world!", Toast.LENGTH_LONG).show();

   }

});

Xtendroid code:

import static extension org.xtendroid.utils.AlertUtils.* // for toast(), etc.

// myButton references getMyButton(), a lazy-getter generated by @AndroidActivity

myButton.onClickListener = [View v|    // Lambda - params are optional

   toast("Hello, world!")

]

Note: Semi-colons optional, compact and differentiating lambda syntax, getters/setters as properties.

Type Inference

Android code:

// Store JSONObject results into an array of HashMaps

ArrayList<HashMap<String,JSONObject>> results = new ArrayList<HashMap<String,JSONObject>>();

HashMap<String,JsonObject> result1 = new HashMap<String,JSONObject>();

result1.put("result1", new JSONObject());

result2.put("result2", new JSONObject());

results.put(result1);

results.put(result2);

Xtendroid (Xtend) code:

var results = #[

    #{ "result1" -> new JSONObject },

    #{ "result2" -> new JSONObject }

]

Note: compact notation for Lists and Maps, method call brackets are optional

Multi-threading

Blink a button 3 times (equivalent Android code is too verbose to include here):

import static extension org.xtendroid.utils.AsyncBuilder.*

// Blink button 3 times using AsyncTask

async [

    // this is the doInBackground() code, runs in the background

    for (i : 1..3) { // number ranges, nice!

        runOnUiThread [ myButton.pressed = true ]

        Thread.sleep(250) // look ma! no try/catch!

        runOnUiThread [ myButton.pressed = false ]

        Thread.sleep(250)

    }

    return true

].then [result|

    // This is the onPostExecute() code, runs on UI thread

    if (result) {

        toast("Done!")

    }

].onError [error|

    toast("Oops! " + error.message)

].start()

Note: sneaky throws, smoother error handling. See documentation for the many other benefits to using the AsyncBuilder.

Android boilerplate removal

Creating a Parcelable in Android:

public class Student implements Parcelable {

    private String id;

    private String name;

    private String grade;

    // Constructor

    public Student(){

    }

    // Getter and setter methods

    // ... ommitted for brevity!

    // Parcelling part

    public Student(Parcel in){

        String[] data = new String[3];

        in.readStringArray(data);

        this.id = data[0];

        this.name = data[1];

        this.grade = data[2];

    }

    @Оverride

    public int describeContents(){

        return 0;

    }

    @Override

    public void writeToParcel(Parcel dest, int flags) {

        dest.writeStringArray(new String[] {this.id,

                                            this.name,

                                            this.grade});

    }

    public static final Parcelable.Creator CREATOR = new Parcelable.Creator() {

        public Student createFromParcel(Parcel in) {

            return new Student(in); 

        }

        public Student[] newArray(int size) {

            return new Student[size];

        }

    };

}

Xtendroid:

// @Accessors creates getters/setters, @AndroidParcelable makes it parcelable!

@Accessors @AndroidParcelable class Student {

    String id

    String name

    String grade

}

Note: the above Xtendroid code essentially generates the same Android code above, into the build/generated folder, which gets compiled normally. Full bi-directional interoperability with existing Java classes.

Functional programming

@Accessors class User {

    String username

    long salary

    int age

}

var List<User> users = getAllUsers() // from somewhere...

var result = users.filter[ age >= 40 ].maxBy[ salary ]

toast('''Top over 40 is «result.username» earning «result.salary»'''

Note: String templating, many built-in list comprehension functions, lambdas taking a single object parameter implicitly puts in scope.

Builder pattern

// Sample Builder class to create UI widgets, like Kotlin's Anko

class UiBuilder {

   def static LinearLayout linearLayout(Context it, (LinearLayout)=>void initializer) {

      new LinearLayout(it) => initializer

   }

   def static Button button(Context it, (Button)=>void initializer) {

      new Button(it) => initializer

   }

} 

// Now let's use it!

import static extension org.xtendroid.utils.AlertUtils.*

import static extension UiBuilder.*

contentView = linearLayout [

   gravity = Gravity.CENTER

   addView( button [

      text = "Say Hello!"

      onClickListener = [ 

         toast("Hello Android from Xtendroid!")

      ]

   ])

]

Note: You can create your own project-specific DSL!

Utilities

import static extension org.xtendroid.utils.AlertUtils.*

import static extension org.xtendroid.utils.TimeUtils.*

var Date yesterday = 24.hours.ago

var Date tomorrow = 24.hours.fromNow

var Date futureDate = now + 48.days + 20.hours + 2.seconds

if (futureDate - now < 24.hours) {

    confirm("Less than a day to go! Do it now?") [

        // user wants to do it now

        doIt()

    ] 

}

Note: using all of the above makes writing unit tests and instrumentation tests very easy, and fun!

巴特西

Android特定语言 Xtendroid

最新文章

热门文章