在选项卡更改时调用 Android 片段 oncreateview [英] Android fragment oncreateview called on tab change

问题描述

我使用 Android 已经有一段时间了，但 Fragment 对我来说有点新(可能对大多数人来说都是如此).无论如何，我有下面的代码，它工作正常.我有三个片段，每个选项卡中都有一个.我想知道每次切换选项卡时调用 onCreateView 是否正常，这样做有意义吗?每次选项卡更改时不应该有一种方法不重绘片段吗?

I've been working with Android for a while, but fragments are a little new to me (as they are to most people probably). Anyway, I've got the below code, and it works fine. I've got three fragments, one in each tab. I'm wondering if it's normal for onCreateView to be called everytime I switch tabs, and does it make sense to do so? Shouldn't there be a way to NOT redraw the fragment every time the tab changes?

我正在从一个有 3 个活动的应用程序转换它，每个选项卡中有一个活动，每次选项卡更改时重新创建视图似乎是一种浪费，而以前在选项卡之间存在视图就可以了变化...

I'm converting this from an app that had 3 activities, one in each tab, and it seems like a waste to recreate the view every time the tab changes, when it used to be just fine having the views exist between tab changes...

顺便说一句，此代码借用自:http://thepseudocoder.wordpress.com/2011/10/04/android-tabs-the-fragment-way/

BTW, this code borrowed from: http://thepseudocoder.wordpress.com/2011/10/04/android-tabs-the-fragment-way/

public class Tabs extends FragmentActivity implements
    TabHost.OnTabChangeListener {

final String MAP_TAB = "Map";
final String IMAGES_TAB = "Images";
final String SETTINGS_TAB = "Settings";

TabHost mTabHost;
HashMap<String, TabInfo> mapTabInfo = new HashMap<String, TabInfo>();
TabInfo mLastTab = null;

private class TabInfo {
    private String tag;
    private Class clss;
    private Bundle args;
    private Fragment fragment;
    TabInfo(String tag, Class clazz, Bundle args) {
        this.tag = tag;
        this.clss = clazz;
        this.args = args;
    }

}

class TabFactory implements TabContentFactory {

    private final Context mContext;

    public TabFactory(Context context) {
        mContext = context;
    }

    public View createTabContent(String tag) {
        View v = new View(mContext);
        v.setMinimumWidth(0);
        v.setMinimumHeight(0);
        return v;
    }

}

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    setContentView(R.layout.main);

    initialiseTabHost(savedInstanceState);
    if (savedInstanceState != null)
        mTabHost.setCurrentTabByTag(savedInstanceState.getString("tab")); //set the tab as per the saved state
}

protected void onSaveInstanceState(Bundle outState) {
    outState.putString("tab", mTabHost.getCurrentTabTag()); //save the tab selected
    super.onSaveInstanceState(outState);
}

private void initialiseTabHost(Bundle args) {
    mTabHost = (TabHost)findViewById(android.R.id.tabhost);
    mTabHost.setup();
    TabInfo tabInfo;

    Tabs.addTab(this,
            mTabHost,
            mTabHost.newTabSpec(MAP_TAB).setIndicator(
                    MAP_TAB,
                    getResources().getDrawable(R.drawable.ic_tab_map_states)),
            ( tabInfo = new TabInfo(MAP_TAB, HMapFragment_NEW.class, args)));
    mapTabInfo.put(tabInfo.tag, tabInfo);

    Tabs.addTab(this,
            mTabHost,
            mTabHost.newTabSpec(IMAGES_TAB).setIndicator(
                    IMAGES_TAB,
                    getResources().getDrawable(R.drawable.ic_tab_gallery_states)),
            ( tabInfo = new TabInfo(IMAGES_TAB, ImageGridFragment.class, args)));
    mapTabInfo.put(tabInfo.tag, tabInfo);

    Tabs.addTab(this,
            mTabHost,
            mTabHost.newTabSpec(SETTINGS_TAB).setIndicator(
                    SETTINGS_TAB,
                    getResources().getDrawable(R.drawable.ic_tab_settings_states)),
            ( tabInfo = new TabInfo(SETTINGS_TAB, SettingsFragment.class, args)));
    mapTabInfo.put(tabInfo.tag, tabInfo);

    // Default to first tab
    this.onTabChanged(MAP_TAB);
    mTabHost.setOnTabChangedListener(this);
}

private static void addTab(Tabs activity, TabHost tabHost, TabHost.TabSpec tabSpec, TabInfo tabInfo) {
    // Attach a Tab view factory to the spec
    tabSpec.setContent(activity.new TabFactory(activity));
    String tag = tabSpec.getTag();

    // Check to see if we already have a fragment for this tab, probably
    // from a previously saved state.  If so, deactivate it, because our
    // initial state is that a tab isn't shown.
    tabInfo.fragment = activity.getSupportFragmentManager().findFragmentByTag(tag);
    if (tabInfo.fragment != null && !tabInfo.fragment.isDetached()) {
        FragmentTransaction ft = activity.getSupportFragmentManager().beginTransaction();
        ft.detach(tabInfo.fragment);
        ft.commit();
        activity.getSupportFragmentManager().executePendingTransactions();
    }

    tabHost.addTab(tabSpec);
}

public void onTabChanged(String tag) {
    TabInfo newTab = this.mapTabInfo.get(tag);
    // if they've clicked to change tabs
    if (mLastTab != newTab) {
        FragmentTransaction ft = this.getSupportFragmentManager().beginTransaction();
        if (mLastTab != null)
            if (mLastTab.fragment != null) ft.detach(mLastTab.fragment);
        if (newTab != null) {
            if (newTab.fragment == null) {
                newTab.fragment = Fragment.instantiate(this, newTab.clss.getName(), newTab.args);
                ft.add(R.id.realtabcontent, newTab.fragment, newTab.tag);
            } else ft.attach(newTab.fragment);
        }

        mLastTab = newTab;
        ft.commit();
        this.getSupportFragmentManager().executePendingTransactions();
    }
}
}

推荐答案

有 3 种方法可以从视图中移除 Fragment:

There a 3 ways to remove a Fragment from view:

• 隐藏它(hide 对交易对象的功能)
• 分离它(交易对象上的detach函数)
• 移除它(交易对象上的remove函数)

• Hide it (hide function on transaction object)
• Detach it (detach function on transaction object)
• Remove it (remove function on transaction object)

如果您隐藏它，视图将被隐藏，但仍位于布局中并且应该保持不变.如果您分离它，视图将被拆除，但片段仍由 FragmentManager 管理(例如，将在配置更改时重新创建).如果您删除，它将完全从 FragmentManager 中删除，并且将不再管理其状态.

If you hide it the view gets hidden, but is still in the layout and should stay intact. If you detach it, the view gets torn down, but the fragment is still managed by the FragmentManager (and will be recreated on a configuration change, for example). If you remove it it gets removed from the FragmentManager completely and it's state will no longer be managed.

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