Category Archives: Kotlin

Android coding log


Button btn = (Button) findViewById(;
btn.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            /* action here*/

setOnClickListener Method传递一个OnClickListener Interface Object. 从而Interface的OnClick方法被调用.

Kotlin的{} curly braces 可以是一个匿名函数Anonymous functions , shell 里面叫group command .

Java 子类不能override 父类没有定义的method.

The Activity class is a crucial component of an Android app, and the way activities are launched and put together is a fundamental part of the platform’s application model. Unlike programming paradigms in which apps are launched with a main() method, the Android system initiates code in an Activity instance by invoking specific callback methods that correspond to specific stages of its lifecycle.

A Fragment represents a behavior or a portion of user interface in a FragmentActivity. You can combine multiple fragments in a single activity to build a multi-pane UI and reuse a fragment in multiple activities. You can think of a fragment as a modular section of an activity, which has its own lifecycle, receives its own input events, and which you can add or remove while the activity is running (sort of like a “sub activity” that you can reuse in different activities).


Interfaces in Kotlin can contain declarations of abstract methods, as well as method implementations. What makes them different from abstract classes is that interfaces cannot store state. They can have properties but these need to be abstract or to provide accessor implementations.