纯代码简单控件

package com.example.bluegrey.myapplication;

import android.graphics.Color;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Gravity;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.TextView;

public class FirstActivity extends AppCompatActivity {

TextView textView;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    LinearLayout  linearLayout=new LinearLayout(this);
    linearLayout.setOrientation(LinearLayout.VERTICAL);
    linearLayout.setBackgroundColor(Color.GREEN);

    setContentView(linearLayout);


    Button button = new Button(this);

    button.setText("Click me");

    linearLayout.addView(button);

    LinearLayout.LayoutParams layoutParams=new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT,LinearLayout.LayoutParams.WRAP_CONTENT);

    layoutParams.gravity= Gravity.CENTER;

    button.setLayoutParams(layoutParams);

    final TextView textView=new TextView(this);

    textView.setText("hello world!");

    textView.setLayoutParams(layoutParams);

    linearLayout.addView(textView);

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            textView.setText("I am happy");
        }
    });


}

}