由于网络数据的加载存在于不同的界面之中，当快速的切换界面时，就会出现程序的出错。因为快速的切换时，当前界面的数据还在读取，就切换到下一个界面，下一个界面也开始加载数据，每次界面的切换都会加载数据。这样就会出错（在本文中，fragment 是使用 replace() 方法来加载界面的，）。所以可以使每个 fragment 只加载一次来减少数据的加载次数。当然可以使用缓存技术来解决问题。
本文中只使用 fragment 的隐藏或者加载来实现每个界面只加载一次。这时需要多定义一个 Fragment 变量，以充当中间的变量，来实现 fragment 的隐藏。
上文中界面切换的效果，其实很简单，即：点击当前 TextView 使其颜色改变，其他的 TextView 的颜色都变为相同颜色即可。这时可以把这些变化封装为一个方法。减少代码量。
package com.crazy.gemi; import android.app.SearchManager;import android.content.Intent;import android.graphics.Color;import android.provider.SearchRecentSuggestions;import android.support.v4.app.Fragment;import android.support.v4.app.FragmentActivity;import android.os.Bundle;import android.support.v4.app.FragmentTransaction;import android.view.View;import android.widget.TextView; import com.crazy.gemi.ui.cheaper.CheaperFragment;import com.crazy.gemi.ui.cheaper.SearchSuggestionSampleProvider;import com.crazy.gemi.ui.favor.FavorFragment;import com.crazy.gemi.ui.more.MoreFragment;import com.crazy.gemi.ui.near.NearFragment;import com.crazy.gemi.ui.pocket.PocketFragment; public class MainActivity extends FragmentActivity implements View.OnClickListener, CheaperFragment.SearchResult{ private TextView[] textView = new TextView[5]; private View[] views = new View[5]; // 其中的 firstFragment 相当于是个中间变量 private Fragment firstFragment, nearFragment, cheaperFragment, favorFragment, pocketFragmnet, moreFragment; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); init(); initFragment(); } private void init() { textView[0] = (TextView)findViewById(R.id.near); textView[1] = (TextView)findViewById(R.id.search_cheaper); textView[2] = (TextView)findViewById(R.id.favor); textView[3] = (TextView)findViewById(R.id.pocket); textView[4] = (TextView)findViewById(R.id.more); views[0] = findViewById(R.id.near_top_line); views[1] = findViewById(R.id.cheaper_top_line); views[2] = findViewById(R.id.favor_top_line); views[3] = findViewById(R.id.pocket_top_line); views[4] = findViewById(R.id.more_top_line); textView[0].setOnClickListener(this); textView[1].setOnClickListener(this); textView[2].setOnClickListener(this); textView[3].setOnClickListener(this); textView[4].setOnClickListener(this); } private void initFragment() { firstFragment = FavorFragment.newInstance(); favorFragment = firstFragment; // 最先加载的 fragment getSupportFragmentManager().beginTransaction(). add(R.id.frame_layout, favorFragment).commit(); textView[2].setTextColor(Color.BLACK); views[2].setBackgroundColor(Color.parseColor("#FF6600")); } @Override public void onClick(View v) { switch (v.getId()) { case R.id.near:// getSupportFragmentManager().beginTransaction().// replace(R.id.frame_layout, NearFragment.newInstance()).commit(); if(nearFragment==null){ nearFragment= NearFragment.newInstance(); } switchContent(firstFragment, nearFragment, getSupportFragmentManager().beginTransaction()); firstFragment = nearFragment; selectStringAndBackgroundColor(0); break; case R.id.search_cheaper: if(cheaperFragment==null){ cheaperFragment= CheaperFragment.newInstance(); } switchContent(firstFragment, cheaperFragment, getSupportFragmentManager().beginTransaction()); firstFragment = cheaperFragment; selectStringAndBackgroundColor(1); break; case R.id.favor: if(favorFragment==null){ favorFragment= FavorFragment.newInstance(); } switchContent(firstFragment, favorFragment, getSupportFragmentManager().beginTransaction()); firstFragment = favorFragment; selectStringAndBackgroundColor(2); break; case R.id.pocket: if(pocketFragmnet==null){ pocketFragmnet= PocketFragment.newInstance(); } switchContent(firstFragment, pocketFragmnet, getSupportFragmentManager().beginTransaction()); firstFragment = pocketFragmnet; selectStringAndBackgroundColor(3); break; case R.id.more: if(moreFragment==null){ moreFragment= MoreFragment.newInstance(); } switchContent(firstFragment, moreFragment, getSupportFragmentManager().beginTransaction()); firstFragment = moreFragment; selectStringAndBackgroundColor(4); break; } } /** * 通过 position 的位置改变文字和 View 的颜色 * @param position */ private void selectStringAndBackgroundColor(int position){ int sum = textView.length; for (int i = 0; i < sum; i++) { if (position == i) { textView[i].setTextColor(Color.BLACK); views[i].setBackgroundColor(Color.parseColor("#FF6600")); } else { textView[i].setTextColor(Color.GRAY); views[i].setBackgroundColor(Color.parseColor("#f0f0f0")); } } } /** * 判断是否添加了界面，以保存当前状态 */ public void switchContent(Fragment from, Fragment to, FragmentTransaction transaction) { if (!to.isAdded()) { // 先判断是否被add过 transaction.hide(from).add(R.id.frame_layout, to) .commit(); // 隐藏当前的fragment，add下一个到Activity中 } else { transaction.hide(from).show(to).commit(); // 隐藏当前的fragment，显示下一个 } } } 
