Android：如何从 Fragment onCreateView() 访问 Activity 的视图（使用 findViewById）？

Question

我有一个非常简单的项目，其中包含一个片段的 Activity。您可能不熟悉的唯一一件事是我使用的是VideoEnabledWebView，它并不复杂，并且是我以前使用过的东西。这只是一个自定义的 webview。

这是我的代码：

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>

<!-- Don't forget the internet permission if you will be using the WebView to load remote content -->
<uses-permission android:name="android.permission.INTERNET" />

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme"
    android:hardwareAccelerated="true" > <!-- Only works in API level 11+, and allows the HTML5 videos to play in-line -->

    <activity
        android:name="name.cpr.ExampleActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

ExampleActivity.java

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;

import cpr.name.videoenabledwebview.R;

public class ExampleActivity extends Activity
{
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        Log.i("rai", "activity onCreate");
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_example);

    }

}

activity_example.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".ExampleActivity">

<!-- View that will be hidden when video goes fullscreen -->
<RelativeLayout
    android:id="@+id/nonVideoLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <fragment android:name="name.cpr.WebViewFragment"
        android:id="@+id/webViewFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</RelativeLayout>

<!-- View where the video will be shown when video goes fullscreen -->
<RelativeLayout
    android:id="@+id/videoLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

</RelativeLayout>

WebViewFragment.java

package name.cpr;

import android.app.Activity;
import android.app.Fragment;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import cpr.name.videoenabledwebview.R;


public class WebViewFragment extends Fragment {

private VideoEnabledWebView webView;
private VideoEnabledWebChromeClient webChromeClient;
View rootView;

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    rootView = inflater.inflate(R.layout.root, container, false);

    webView = (VideoEnabledWebView) rootView.findViewById(R.id.webView);

    Log.i("rai", "nonVideoLayout = " + R.id.nonVideoLayout);

    Log.i("rai", "videoLayout = " + R.id.videoLayout);

    View nonVideoLayout = rootView.findViewById(R.id.nonVideoLayout);

    if(nonVideoLayout == null){

        Log.i("rai", "why is nonVideoLayout null?");
    }

    ViewGroup videoLayout = (ViewGroup)     rootView.findViewById(R.id.videoLayout);

    if(videoLayout == null){

        Log.i("rai", "why is videoLayout null?");
    }

    webChromeClient = new VideoEnabledWebChromeClient(nonVideoLayout, videoLayout);

    webView.setWebChromeClient(webChromeClient);

    webView.loadUrl("http://m.youtube.com");

    return rootView;

}
}

root.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">

<TextView
    android:layout_width="100dp"
    android:layout_height="100dp"
    android:text="the fragment"/>

<name.cpr.VideoEnabledWebView
    android:id="@+id/webView"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" />

</LinearLayout>

我只是无法访问我的 Activity 中的这两个相对布局，我一直为空。

我尝试过但不起作用的方法：

rootView.findViewById //rootView是inflate的返回

getActivity().findViewById

getView().findViewById

container.findViewById

我也在我的片段 onCreate 中尝试过这个：

context = getActivity().getApplicationContext();

webViewFragmentId = context.getResources().getIdentifier(
        "root", "layout", context.getPackageName());

webViewId = context.getResources().getIdentifier("webView", "id",
        context.getPackageName());

nonVideoLayoutId = context.getResources().getIdentifier("nonVideoLayout", "id", context.getPackageName());
videoLayoutId = context.getResources().getIdentifier("videoLayout","id", context.getPackageName());

rootView = inflater.inflate(webViewFragmentId, null);

webView = (VideoEnabledWebView) rootView.findViewById(webViewId);

View nonVideoLayout = getActivity().findViewById(nonVideoLayoutId);
ViewGroup videoLayout = (ViewGroup) getActivity().findViewById(videoLayoutId);

webChromeClient = new VideoEnabledWebChromeClient(nonVideoLayout, videoLayout);

webView.setWebChromeClient(webChromeClient);

webView.loadUrl("http://m.youtube.com");


return rootView;

Answer 1

2020 年 10 月 27 日更新

现在 onActivityCreated 已被弃用，documentation 状态您应该注册一个 LifecycleObserver 以了解 Activity.onCreate() 方法何时完成。

有关示例，请参阅 this answer。

---

原答案

您应该覆盖onActivityCreated 并在该方法中从活动中访问您需要的视图，因为当onCreateView 在片段中运行时，活动尚未设置其布局，因此您无法访问其视图。

@Override
public void onActivityCreated (Bundle savedInstanceState) {
    View nonVideoLayout = getActivity().findViewById(R.id.nonVideoLayout);
    ViewGroup videoLayout = (ViewGroup) getActivity().findViewById(R.id.videoLayout);
    ...
}

Answer 2

您需要重写 onActivityCreated()，因为在调用此方法之前不会创建活动视图。

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    View nonVideoLayout = ((MainActivity)getActivity()).findViewById(R.id.nonVideoLayout);

    if(nonVideoLayout == null){

        Log.e("rai", "why is nonVideoLayout null?");
    }
    else{
        Log.e("rai", "view not null hurray");
    }
    View videoLayout =    getActivity().findViewById(R.id.videoLayout);

    if(videoLayout == null){

        Log.e("rai", "why is videoLayout null?");
    }else{
        Log.e("rai", "view not null hurray");
    }

Answer 3

您需要覆盖 onViewCreated。视图不是在 onCreate 中创建的，而是在实际创建视图后创建的。这篇文章提供了更多信息Difference between onCreateView and onViewCreated in Fragment

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    ...
}