Android组件：Fragment切换后保存状态

转载

mb5fe55bba5ad74 2017-08-02 09:59:00

文章标签 ide 微信生命周期 javascript 初始化 文章分类 JavaScript 前端开发

之前写的第一篇Fragment实例，和大多数人一開始学的一样。都是通过FragmentTransaction的replace方法来实现，replace方法相当于先移除remove()原来全部已存在的fragments，然后加入add()当前这个fragment。这就导致了一个问题，我们切换一次，然后再切换回来，相当于又一次载入了这个fragment，原来的状态不复存在，这显然与我们的日常使用不符。

想要保存切换后的状态。思路还是非常easy的。我们先加入了若干fragments。切换后将全部fragments都隐藏hide()。并显示show()切换后的fragment就可以。

实例：山寨微信

因为代码较长。这里仅仅讲核心的部分，有兴趣的能够下载源代码来看一下

public class MainActivity extends ActionBarActivity implements OnClickListener {

  private View weixinLayout, tongxunluLayout, faxianLayout, woLayout;
  private TextView weixinTv, tongxunluTv, faxianTv, woTv;
  private ImageView weixinIv, tongxunluIv, faxianIv, woIv;
  private Fragment1 fragment1;
  private Fragment2 fragment2;
  private Fragment3 fragment3;
  private Fragment4 fragment4;
  private FragmentManager fm;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    // 初始化
    initViews();

    fm = getFragmentManager();

    // 初识状态是显示微信
    weixinIv.setBackgroundResource(R.drawable.weixin2);
    weixinTv.setTextColor(getResources().getColor(R.color.green));
    showFragment(1);
  }

  void initViews() {
    // 注冊各IamgeView
    weixinIv = (ImageView) findViewById(R.id.weixin_iv);
    tongxunluIv = (ImageView) findViewById(R.id.tongxunlu_iv);
    faxianIv = (ImageView) findViewById(R.id.faxian_iv);
    woIv = (ImageView) findViewById(R.id.wo_iv);

    // 注冊各TextView
    weixinTv = (TextView) findViewById(R.id.weixin_tv);
    tongxunluTv = (TextView) findViewById(R.id.tongxunlu_tv);
    faxianTv = (TextView) findViewById(R.id.faxian_tv);
    woTv = (TextView) findViewById(R.id.wo_tv);

    // 注冊各Layout
    weixinLayout = (View) findViewById(R.id.weixin_layout);
    tongxunluLayout = (View) findViewById(R.id.tongxunlu_layout);
    faxianLayout = (View) findViewById(R.id.faxian_layout);
    woLayout = (View) findViewById(R.id.wo_layout);

    // 各Layout注冊监听器
    weixinLayout.setOnClickListener(this);
    tongxunluLayout.setOnClickListener(this);
    faxianLayout.setOnClickListener(this);
    woLayout.setOnClickListener(this);

  }

  @Override
  public void onClick(View arg0) {
    // TODO Auto-generated method stub
    // 当点击某个layout时。先清除状态。这里的状态指的是布局里面的图片和文字
    clearState();
    switch (arg0.getId()) {
    case R.id.weixin_layout:
      // 假设点的是微信。将微信布局的图片和文字的颜色变为绿色
      weixinIv.setBackgroundResource(R.drawable.weixin2);
      weixinTv.setTextColor(getResources().getColor(R.color.green));
      // 显示微信的fragment
      showFragment(1);
      break;
    case R.id.tongxunlu_layout:
      tongxunluIv.setBackgroundResource(R.drawable.tongxunlu2);
      tongxunluTv.setTextColor(getResources().getColor(R.color.green));
      showFragment(2);
      break;
    case R.id.faxian_layout:
      faxianIv.setBackgroundResource(R.drawable.faxian2);
      faxianTv.setTextColor(getResources().getColor(R.color.green));
      showFragment(3);
      break;
    case R.id.wo_layout:
      woIv.setBackgroundResource(R.drawable.wo2);
      woTv.setTextColor(getResources().getColor(R.color.green));
      showFragment(4);
      break;
    }
  }

  public void clearState() {
    // 未选中时的图片
    weixinIv.setBackgroundResource(R.drawable.weixin1);
    tongxunluIv.setBackgroundResource(R.drawable.tongxunlu1);
    faxianIv.setBackgroundResource(R.drawable.faxian1);
    woIv.setBackgroundResource(R.drawable.wo1);
    // 未选中时字体颜色
    weixinTv.setTextColor(getResources().getColor(R.color.black));
    tongxunluTv.setTextColor(getResources().getColor(R.color.black));
    faxianTv.setTextColor(getResources().getColor(R.color.black));
    woTv.setTextColor(getResources().getColor(R.color.black));
  }

  public void showFragment(int index) {
    FragmentTransaction ft = fm.beginTransaction();

    // 想要显示一个fragment,先隐藏全部fragment。防止重叠
    hideFragments(ft);

    switch (index) {
    case 1:
      // 假设fragment1已经存在则将其显示出来
      if (fragment1 != null)
        ft.show(fragment1);
      // 否则是第一次切换则加入fragment1，注意加入后是会显示出来的。replace方法也是先remove后add
      else {
        fragment1 = new Fragment1();
        ft.add(R.id.content, fragment1);
      }
      break;
    case 2:
      if (fragment2 != null)
        ft.show(fragment2);
      else {
        fragment2 = new Fragment2();
        ft.add(R.id.content, fragment2);
      }
      break;
    case 3:
      if (fragment3 != null)
        ft.show(fragment3);
      else {
        fragment3 = new Fragment3();
        ft.add(R.id.content, fragment3);
      }
      break;
    case 4:
      if (fragment4 != null)
        ft.show(fragment4);
      else {
        fragment4 = new Fragment4();
        ft.add(R.id.content, fragment4);
      }
      break;
    }
    ft.commit();
  }

  // 当fragment已被实例化，就隐藏起来
  public void hideFragments(FragmentTransaction ft) {
    if (fragment1 != null)
      ft.hide(fragment1);
    if (fragment2 != null)
      ft.hide(fragment2);
    if (fragment3 != null)
      ft.hide(fragment3);
    if (fragment4 != null)
      ft.hide(fragment4);
  }

}