安卓加载顺序

package com.example.viewpagerok;import java.util.ArrayList;import android.annotation.SuppressLint;import android.app.Activity;import android.os.Bundle;import android.support.v4.view.PagerAdapter;import android.support.v4.view.ViewPager;import android.view.LayoutInflater;import android.view.Menu;import android.view.MenuItem;import android.view.View;import android.view.View.OnClickListener;import android.view.ViewGroup;import android.widget.TextView;import android.widget.Toast;@SuppressLint({ "InflateParams", "ShowToast" })public class MainActivity extends Activity {ArrayList<View> arrayList;ViewPager viewPager;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);TextView textView = (TextView) findViewById(R.id.textView1);TextView textView1 = (TextView) findViewById(R.id.textView2);TextView textView2 = (TextView) findViewById(R.id.textView3);textView.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubviewPager.setCurrentItem(0);Toast.makeText(MainActivity.this, "1", 1).show();}});textView1.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubviewPager.setCurrentItem(1);Toast.makeText(MainActivity.this, "2", 1).show();}});textView2.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubviewPager.setCurrentItem(2);Toast.makeText(MainActivity.this, "3", 1).show();}});////为什么在viewpager实例化之前可以调用呢？因为，oncreate函数不是一行一行按照顺序，首先寻找的实例的代码，所以不会报错，第一步加载的层次是实例化层次，所有实例化都会在第一批加载，Java是按次序的，安卓是按层次，然后再按次序的。arrayList = new ArrayList<View>();arrayList.add(LayoutInflater.from(MainActivity.this).inflate(R.layout.page1, null));arrayList.add(LayoutInflater.from(MainActivity.this).inflate(R.layout.page2, null));arrayList.add(LayoutInflater.from(MainActivity.this).inflate(R.layout.page3, null));viewPager = (ViewPager) findViewById(R.id.viewPager);viewPager.setAdapter(new dxc());}class dxc extends PagerAdapter {@Overridepublic int getCount() {// TODO Auto-generated method stubreturn arrayList.size();}@Overridepublic boolean isViewFromObject(View arg0, Object arg1) {// TODO Auto-generated method stubreturn arg0 == arg1;}@Overridepublic void destroyItem(ViewGroup container, int position, Object object) {// TODO Auto-generated method stub((ViewPager) container).removeView(arrayList.get(position));}@Overridepublic Object instantiateItem(ViewGroup container, int position) {// TODO Auto-generated method stub((ViewPager) container).addView(arrayList.get(position), 0);return arrayList.get(position);}}@Overridepublic 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;}@Overridepublic boolean onOptionsItemSelected(MenuItem item) {// Handle action bar item clicks here. The action bar will// automatically handle clicks on the Home/Up button, so long// as you specify a parent activity in AndroidManifest.xml.int id = item.getItemId();if (id == R.id.action_settings) {return true;}return super.onOptionsItemSelected(item);}}public class MainActivity extends Activity { Button button;String a;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        button=(Button)findViewById(R.id.button1);        button.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubbutton.setText(a);//第二层，执行button行为，第一层加载的a已经实例化}});        a=new String("1");//实例化，第一层加载            }    @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;    }    @Override    public boolean onOptionsItemSelected(MenuItem item) {        // Handle action bar item clicks here. The action bar will        // automatically handle clicks on the Home/Up button, so long        // as you specify a parent activity in AndroidManifest.xml.        int id = item.getItemId();        if (id == R.id.action_settings) {            return true;        }        return super.onOptionsItemSelected(item);    }}