编程实现颜色变幻

package com.example.ok4;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.graphics.Color;

public class MainActivity extends Activity {

 private LinearLayout linearlayout;    //声明LinearLayout
 private LinearLayout.LayoutParams layoutparams;   //声明LayoutParams
 private TextView tv_blue,tv_black,tv_yellow;              //声明TextView
 private int wc=LinearLayout.LayoutParams.WRAP_CONTENT;   //声明一个int型的 wc=LinearLayout.LayoutParams.WRAP_CONTENT;
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  linearlayout=new LinearLayout(this);    //初始化一个LinearLayout
  linearlayout.setOrientation(LinearLayout.VERTICAL);  //设置LinearLayout方向是垂直
  linearlayout.setBackgroundColor(Color.RED);    //设置背景色是红色
  setContentView(linearlayout);  //显示出来LinearLayout
  layoutparams=new LinearLayout.LayoutParams(wc,wc);  //初始化一个LayoutParams
  addText();   //初始化TextView并设置值
  addTextView();  //把TextView添加到LinearLayout中
 }
 
 public void addText()
 {
  tv_blue=new TextView(this);
  tv_black=new TextView(this);
  tv_yellow=new TextView(this);
  tv_blue.setText("blue");
  tv_blue.setTextColor(Color.BLUE);
  tv_black.setText("black");
  tv_black.setTextColor(Color.BLACK);
  tv_yellow.setText("yellow");
  tv_yellow.setTextColor(Color.YELLOW);
 }
 
 public void addTextView()
 {
  linearlayout.addView(tv_blue,layoutparams); 
  linearlayout.addView(tv_black,layoutparams);
  linearlayout.addView(tv_yellow,layoutparams);
 }

 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
  // Inflate the menu; this adds items to the action bar if it is present.
  getMenuInflater().inflate(R.menu.main, menu);
  return true;
 }

}