即使在 oncreate 方法中没有调用它们，为什么 android 也会运行像“onItemSelected”这样的方法？

Question

Hello everyone i begin to learn Android development and i do not Unterstand how it works. I understood that there is not a main. Instead it is the android lifecyle. But now i do not Unterstand why methods like "onItemSelected" or "onTouchEvent" executes by android even if tbis methods do not called.

Answer 1

Tahir!

These methods are listeners, so they are listening to the special action you make. They will be called every time you select the item or touch a UI stuff you are listening to. For example, there is a method called setOnClickListener which listens every time you click on something, eg any button you have. The syntaxis will be like:

final Button button = (Button) findViewById(R.id.my_cool_button);
button.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
        // your handler code here
    }
});

It will be called on touch your button no matter where it is.