从活动访问片段的视图

Posted 2023-02-19

【中文标题】从活动访问片段的视图

【英文标题】：Accessing fragment's view from an activity

【发布时间】：2014-08-30 19:56:17

【问题描述】：

我有一个包含片段的活动，它通过在 onCreate 中执行此操作来添加它（来自 Google 示例）：

    // Check that the activity is using the layout version with
    // the fragment_container FrameLayout
    if (findViewById(R.id.fragment_container) != null) 

        // However, if we're being restored from a previous state,
        // then we don't need to do anything and should return or else
        // we could end up with overlapping fragments.
        if (savedInstanceState != null) 
            return;
        

        // Create a new Fragment to be placed in the activity layout
        RecordFragment firstFragment = new RecordFragment();

        // In case this activity was started with special instructions from an
        // Intent, pass the Intent's extras to the fragment as arguments
        firstFragment.setArguments(getIntent().getExtras());

        // Add the fragment to the 'fragment_container' FrameLayout
        getSupportFragmentManager().beginTransaction()
                .add(R.id.fragment_container, firstFragment).commit();

这是活动布局：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/fragment_container"
android:layout_
android:layout_ />

这是片段：

public class RecordFragment extends Fragment 

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
    Bundle savedInstanceState) 
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_record, container, false);

还有fragment_record.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/LinearLayout1"
android:layout_
android:layout_
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.controlcenter.RecordActivity$PlaceholderFragment" >

<TextView
    android:id="@+id/textView1"
    android:layout_
    android:layout_
    android:text="Information:"
    android:textAppearance="?android:attr/textAppearanceMedium" />

<LinearLayout
    android:layout_
    android:layout_ >

    <EditText
        android:id="@+id/action_info"
        android:layout_
        android:layout_
        android:layout_weight="1"
        android:ems="10" />

    <ImageView
        android:id="@+id/arrow_button"
        android:layout_
        android:layout_
        android:src="@drawable/ic_action_forward" />

</LinearLayout>

片段中有一个箭头按钮。我希望活动向按钮添加一个侦听器，以便在单击它时，片段将滑出，另一个片段将滑入。 我无法访问该按钮，我正在尝试使用

firstFragment.getView().findViewById(R.id.arrow_button)

但似乎 getView 正在返回 null，尽管我重载了 onCreateView() 方法。

【参考方案1】：

简单的答案是你不知道。将 Fragment 的视图视为 Fragment 内部的东西。相反，通过您定义的接口将 Activity 设置为 Fragment 的侦听器，然后在 Fragment 中设置点击侦听器以调用 Fragment 的侦听器。

public class MyFragment extends Fragment 
    public interface MyListener 
        public void onAction();
    

    private MyListener mListener;
    public void setListener(MyListener listener) 
        mListener = listener;
    

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) 
        View root = inflater.inflate(R.layout.fragment_record, container, false);

        root.findViewById(R.id.arrow_button).setOnClickListener(new OnClickListener() 
            @Override
            public void onClick(View view) 
                if (mListener != null) 
                    mListener.onAction();
                
            
        );
        return root;
    
    @Override
    public void onAttach(Activity activity) 
        super.onAttach(activity);
        if (activity instanceof MyListener) 
            mListener = (MyListener) activity;
         else 
            // Maybe throw an exception if you want to be strict
        
    

你的 Activity 类需要这个：

public class MyActivity extends Activity implements MyFragment.MyListener 
    public void onAction() 
        // TODO whatever you need to do when the button is clicked