不调用嵌套片段的 onCreateView() [英] onCreateView() of nested fragment is not called

问题描述

我一直在浏览 StackOverflow 中的嵌套片段文档、最佳实践和所有可能的链接.我看到了一些建议，以避免在布局文件中使用片段标记，而是通过事务添加它们以实现无缝过渡.

I have been going through nested fragments documentation, best practices and all possible links here in StackOverflow. I have seen suggestions to avoid using fragment tag in layout files and instead add them via transaction for seamless transitions.

在我的应用程序中实现它之前，我尝试了一个简单的例子，我发现了一些意想不到的行为，没有调用 onCreateView() 子片段.我认为，我在理解中遗漏了一些东西，所以我正在寻找一些建议/帮助来解决这个问题.

Before implementing it in my app, I tried a simple example and I found some unexpected behavior, child fragments onCreateView() is not getting called. I assume that , I am missing something in my understanding, so I am looking for some advice/help to sort this out.

示例流程如下:--

MainActivity 托管一个片段(MessageFragment)，MessageFragment 托管一个子片段(MessageTextFragment).

MainActivity hosts a fragment(MessageFragment) and the MessageFragment hosts a child fragment(MessageTextFragment).

我使用片段事务以编程方式添加子片段.但是子片段的 onCreateView 永远不会被调用，因此子视图不会膨胀.

I add the child fragment programatically using fragment transaction. But onCreateView of the child fragment never gets called, because of which the sub-view is not inflated.

我正在使用 v4 支持库来处理各处的片段这是我的完整代码:--

I am using v4 support library for fragments everywhere Here is my complete code:--

主活动文件:--

 public class MainActivity extends AppCompatActivity {
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.root_layout);
            FragmentManager fragmentManager = getSupportFragmentManager();
            Fragment fragment = null;
            if (savedInstanceState == null) {
                FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
                fragment=new MessageFragment().newInstance();
                fragmentTransaction.add(R.id.fragment_container, fragment);
                fragmentTransaction.commit();
            }
        }
}

MainActivity 的布局文件:-

layout file for MainActivity:-

<RelativeLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:id="@+id/wizard_layout_root"
        android:paddingLeft="5dp"
        android:paddingRight="5dp"
        android:orientation="vertical">
    <FrameLayout
        android:id="@+id/fragment_container"
        android:layout_height="fill_parent"
        android:layout_width="fill_parent"/>
</RelativeLayout>

第一个Fragment是:MessageFragment--

The first Fragment is: MessageFragment--

public class MessageFragment extends Fragment {
    private EditText msgText;

    private Activity activity;

    TextView tvTitle, tvContent, tvIntro;
    Button bAction;

    public static MessageFragment newInstance() {
        MessageFragment f = new MessageFragment();
        return (f);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.message, container, false);
        tvTitle = (TextView) view.findViewById(R.id.fragment_title);
        tvIntro = (TextView) view.findViewById(R.id.fragment_intro);
        tvContent = (TextView) view.findViewById(R.id.fragment_contents);
        bAction = (Button) view.findViewById(R.id.fragment_action);

        Fragment fragment = getChildFragmentManager().findFragmentById(R.id.sms_message);
        if (fragment == null) {
            Log.d("MESSAGE_FRAGMENT", "definetly inside");
            fragment = MessageEditFragment.newInstance();
            FragmentTransaction transaction = getChildFragmentManager().beginTransaction();
            transaction.add(R.id.sms_message, fragment);
            transaction.commit();
            getChildFragmentManager().executePendingTransactions();
            Log.d("MESSAGE_FRAGMENT", "" + getChildFragmentManager().findFragmentById(R.id.sms_message));
        }
        return view;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        activity = getActivity();
        if (activity != null) {
            Fragment fragment = getChildFragmentManager().findFragmentById(R.id.sms_message);
            Log.d("MESSAGE_FRAGMENT", "onActivityCreated" + fragment);
            msgText = (EditText) ((MessageEditFragment)fragment).getView().findViewById(R.id.message_edit_text);
            bAction.setEnabled(!msgText.getText().toString().trim().equals(""));
            msgText.selectAll();
        }
    }
}

MessageFragment 的布局(Framelayout 是子片段的容器)

Layout of MessageFragment(Framelayout is the container for child fragment)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:descendantFocusability="beforeDescendants"
    android:focusableInTouchMode="true"
    android:orientation="vertical">
    <ScrollView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content">
        <RelativeLayout
            android:layout_width="fill_parent"
            android:layout_height="wrap_content">

            <TextView
                android:id="@+id/fragment_title"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_centerHorizontal="true"/>

            <TextView
                android:id="@+id/fragment_intro"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_below="@+id/fragment_title" />

            <LinearLayout
                android:id="@+id/ll_message"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:layout_below="@+id/fragment_intro"
                android:layout_weight="1">
                <FrameLayout
                    android:id="@+id/sms_message"
                    android:layout_width="fill_parent"
                    android:layout_height="fill_parent" />
            </LinearLayout>
            <Button
                android:id="@+id/fragment_action"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:layout_below="@+id/ll_message"/>
        </RelativeLayout>
    </ScrollView>
</LinearLayout>

这是子片段

public class MessageEditFragment extends Fragment {

    private EditText messageEditText;

    private MessageLimitWatcher messageLimitWatcher;
    private int maxCharacters;
    private String messageHeader;
    private Button bAction;

    public static MessageEditFragment newInstance() {
        MessageEditFragment f = new MessageEditFragment();
        return(f);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        Log.d("MESSAGE_FRAGMENT", "onCreateView Of nested fragment");
        View view = inflater.inflate(R.layout.message_fragment, container, false);
        messageEditText = (EditText) view.findViewById(R.id.message_edit_text);
        messageEditText.requestFocus();
        return view;
    }

及其布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_height="wrap_content"
    android:layout_width="fill_parent">
    <RelativeLayout
        android:layout_width="fill_parent"
        android:layout_height="130dp">
        <EditText
            android:id="@+id/message_edit_text"
            android:layout_height="130dp"
            android:layout_width="fill_parent" />
        <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:textColor="@android:color/black"/>
    </RelativeLayout>
</LinearLayout>

Logcat 从不打印该行:--

Logcat never prints the line:--

Log.d("MESSAGE_FRAGMENT", "onCreateView 的嵌套片段");

Log.d("MESSAGE_FRAGMENT", "onCreateView Of nested fragment");

当我尝试使用子片段的文本字段时，我得到一个空指针异常，因为它没有被膨胀.所以基本上，我得到空指针:--

and I get a nullpointer exception when I try to use the text field of child fragment, as it is not inflated.So basically, I get nullpointer at:--

((MessageEditFragment)fragment).getView().findViewById(R.id.message_edit_text);

((MessageEditFragment)fragment).getView().findViewById(R.id.message_edit_text);

推荐答案

不要调用 onCreateView 内部的事务，使用 onActivityCteated 或 onCreate.

Don't call the transactions inside of onCreateView either use onActivityCteated or onCreate.

另外值得注意的是不要调用 executePendingTransactions 当你在父片段的 a 中时，这必然会破坏某些东西.

Also worth noting don't call, executePendingTransactions when you are inside a of the parent fragment, that is bound to break something.

尝试像这样设置你的父片段:

Try to setup your parent fragment something like this:

public class MessageFragment extends Fragment {
  private EditText msgText;

  private Activity activity;

  TextView tvTitle, tvContent, tvIntro;
  Button bAction;

  public static MessageFragment newInstance() {
    MessageFragment f = new MessageFragment();
    return (f);
  }

  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.message, container, false);
    tvTitle = (TextView) view.findViewById(R.id.fragment_title);
    tvIntro = (TextView) view.findViewById(R.id.fragment_intro);
    tvContent = (TextView) view.findViewById(R.id.fragment_contents);
    bAction = (Button) view.findViewById(R.id.fragment_action);
    return view;
  }

  @Override
  public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    activity = getActivity();
    if (activity != null) {
        Fragment fragment = getChildFragmentManager().findFragmentById(R.id.sms_message);
        Log.d("MESSAGE_FRAGMENT", "onActivityCreated" + fragment);
        msgText = (EditText) ((MessageEditFragment)fragment).getView().findViewById(R.id.message_edit_text);
        bAction.setEnabled(!msgText.getText().toString().trim().equals(""));
        msgText.selectAll();
    }
    Fragment fragment = MessageEditFragment.newInstance();
    getChildFragmentManager().beginTransaction()
      .replace(R.id.sms_message, fragment)
      .commit();
  }
}

这篇关于不调用嵌套片段的 onCreateView()的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！