i’d like to avoid parent activity being destroyed whenever i clicked < button in action bar.

按下该按钮后,您的父活动将暂停,而不是被销毁.

is there a way for me to override it? and is there a way to override for all activities?

只需致电：

getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    getSupportActionBar().setHomeButtonEnabled(true);

您需要将其调用到要覆盖按钮的活动.没有其他选择可以称之为“一劳永逸”.

which method is being called from AppCompatActivity when we press that button?

默认情况下,它没有方法.如果您使用工具栏,请在按下该按钮时调用setNavigationOnClickListener()来执行某些操作.

Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    toolbar.setNavigationOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // do something here,such as start an Intent to the parent activity.
        }
    });

如果您使用ActionBar,该按钮将在菜单上可用：

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    if (item.getItemId() == android.R.id.home) {
        // do something here,such as start an Intent to the parent activity.
    }
    return super.onOptionsItemSelected(item);
}