Design UI Layout

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.activity_main); //화면에 보이게 하는 거.

        LinearLayout l = new LinearLayout((this));
        l.setOrientation(LinearLayout.VERTICAL);

        LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
                LinearLayout.LayoutParams.MATCH_PARENT,
                LinearLayout.LayoutParams.MATCH_PARENT
        );

        setContentView(l, params); // 화면에 들어가서 보임.

        Button b = new Button(this);
        b.setText("Button");
        l.addView(b);

    }
}

Add TextView

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.TextView;


public class MainActivity extends AppCompatActivity {

    int count = 1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main); //화면에 보이게 하는 거.

    }

    public void onClick(View view) {
        LinearLayout l = (LinearLayout) findViewById(R.id.LinearLayout);//linearlayout id 설정해야함
        TextView textView = new TextView(this);
        textView.setText("TextView" + count);
        count++;
        l.addView(textView);
    }
}

화면을 넘어갈 때 스크롤을 해주고 싶다.
->ScrollView : 스크롤 뷰 안에 들어있는 애를 스크롤해줌.
스크롤 뷰 안에 스크롤 하고 싶은 애를 넣으면 됨.

텍스트뷰 넣을 때마다 linearlayout이 확장 되는 것을 원하므로 layout_height는 wrap_content로 되어야한다

스크롤이 생성되면서 29아래로 더 보임

Table Layout

stretchedColumns

0, 1, 2 순.
적은 칸이 늘어남

shrinkColumns

layout_column

layout_span

Menu

ctrl + o : overriding 할 수 있는 목록이 나옴

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main); //화면에 보이게 하는 거.

    }

    //...을 누르면 얘가 실행됨
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.sample,menu);
        return true;
    }
}![](https://velog.velcdn.com/images/born_a/post/c03250fc-5c46-421f-a474-540606ba5b9b/image.png)

Handling click events

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main); //화면에 보이게 하는 거.

    }

    //...을 누르면 얘가 실행됨
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.sample,menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.item1:
                Toast.makeText(this,"아이템1",Toast.LENGTH_SHORT).show();
                break;
            case R.id.item2:
                Toast.makeText(this,"아이템2",Toast.LENGTH_SHORT).show();
                break;
            case R.id.item3:
                Toast.makeText(this,"아이템3",Toast.LENGTH_SHORT).show();
                break;
            case R.id.item4:
                Toast.makeText(this,"아이템4",Toast.LENGTH_SHORT).show();
                break;

        }
        return super.onOptionsItemSelected(item);
    }
}

Example) Options Menu

package com.example.myapplication;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.constraintlayout.widget.ConstraintLayout;

import android.graphics.Color;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.Toast;


public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main); //화면에 보이게 하는 거.

    }

    //...을 누르면 얘가 실행됨
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.sample,menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
        ConstraintLayout constraintLayout = (ConstraintLayout) findViewById(R.id.constraintlayout);
        switch (item.getItemId()) {
            case R.id.White:
                Toast.makeText(this,"아이템1",Toast.LENGTH_SHORT).show();
                constraintLayout.setBackgroundColor(Color.rgb(255,255,255));
                break;
            case R.id.Red:
                Toast.makeText(this,"아이템2",Toast.LENGTH_SHORT).show();
                constraintLayout.setBackgroundColor(Color.rgb(255,0,0));
                break;
            case R.id.Green:
                Toast.makeText(this,"아이템3",Toast.LENGTH_SHORT).show();
                constraintLayout.setBackgroundColor(Color.rgb(0,255,0));
                break;
            case R.id.Blue:
                Toast.makeText(this,"아이템4",Toast.LENGTH_SHORT).show();
                constraintLayout.setBackgroundColor(Color.rgb(0,0,255));
                break;

        }
        return super.onOptionsItemSelected(item);
    }
}