onClick

有幾種寫法

1.Lambda

        Button b = findViewById(R.id.button1);
        b.setOnClickListener(view -> {
            System.out.println(123);
            new AlertDialog.Builder(c)
                    .setMessage("test")
                    .show();
        });

2.

final Context c = this;
mButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        // do something here
    }
});

https://stackoverflow.com/questions/30752547/what-does-it-mean-that-a-listener-can-be-replaced-with-lambda