在没有 XML 或布局的情况下向活动添加按钮

Question

Android Studio

We have a project (game) that we need to do android game, a space racing game and we're almost done. We just need to add a retry button and exit button on the game view. The code below is on my GamePlayScene.java and it doesn't have a XML file on the layout folder. They said that it is connected through the game itself. I'm super new to coding a game and on Java language. When I press the start button on the emulator it goes to MainActivty2.java and that MainActivity2 has a XML or on the layout folder but it doesn't have any designs on it, it doesn't have spaceship or anything that we can see if we run the game or start the game on the emulator. So I tried to add a button on that XML and when I tried to press the start button, the message appears "Unfortunately, SpaceRacing has stopped". I hope someone can understand me with this.

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);

    Button button= new Button (this);
    FrameLayout.LayoutParams params = new FrameLayout.LayoutParams(
            FrameLayout.LayoutParams.WRAP_CONTENT,
            FrameLayout.LayoutParams.WRAP_CONTENT);
    params.topMargin = 0;
    params.gravity = Gravity.TOP | Gravity.CENTER_HORIZONTAL;

    button.setText("Retry");
    addContentView(button, params);
    // setContentView(tv);
    button.setOnClickListener(new Button.OnClickListener(){
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(this, MainActivity2.class);
        }

    });
}

The bold letter or has " ** ** " on the code has a red font on the studio.

Answer 1

You need to start with a setContentView so your activity will have an initial layout.

To that method you will pass either a view or a layout id.

So if for example you have a layout file named activity2_layout.xml your onCreate method should look something like this

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity2_layout)

And then you call your button with

findViewById(R.id.buttun_id)

And if you want to add the button there without XML, you first find your layout and then call

myLayout.addView(button)

This is really Android basics, you probably want to take a look at this before proceeding