打开app弹出欢迎界面，然后自动跳转到主界面

//准备跳转的
Timer timer = new Timer();
TimerTask task = new TimerTask() {
@Override
public void run() {
//计算
SharedPreferences preferences = getSharedPreferences("count", MODE_WORLD_READABLE);
//得到次数
int count = preferences.getInt("count", 0);
//跳转页面
Intent intent = new Intent(StartActivity.this, MainActivity.class);
startActivity(intent);
finish();
//得到editor
SharedPreferences.Editor editor = preferences.edit();
//累加
editor.putInt("count", ++count);
//提交
editor.commit();
}
};
timer.schedule(task, 3 * 1000);//3*1000，代表三秒