使用片段：`错误膨胀类片段`答案

【问题标题】：Working With Fragments: `Error inflating class fragment`使用片段：`错误膨胀类片段`
【发布时间】：2016-08-19 05:26:26
【问题描述】：

我正在练习使用 Fragments，并创建了一个测试器来熟悉该过程。

我的目标是创建一个简单的应用程序，它的 ListView 由 10 个字符串组成。 ListView 包含在 MainActivity 中的一个片段中。

但是，我遇到了一个错误...

   FATAL EXCEPTION: main
   Process: com.example.frank.listview_test, PID: 5819
   java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.frank.listview_test/com.example.frank.listview_test.MainActivity}: android.view.InflateException: Binary XML file line #14: Binary XML file line #14: Error inflating class fragment
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3253)
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349)
       at android.app.ActivityThread.access$1100(ActivityThread.java:221)
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
       at android.os.Handler.dispatchMessage(Handler.java:102)
       at android.os.Looper.loop(Looper.java:158)
       at android.app.ActivityThread.main(ActivityThread.java:7224)
       at java.lang.reflect.Method.invoke(Native Method)
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
    Caused by: android.view.InflateException: Binary XML file line #14: Binary XML file line #14: Error inflating class fragment
       at android.view.LayoutInflater.inflate(LayoutInflater.java:551)
       at android.view.LayoutInflater.inflate(LayoutInflater.java:429)
       at android.view.LayoutInflater.inflate(LayoutInflater.java:380)
       at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:284)
       at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140)
       at com.example.frank.listview_test.MainActivity.onCreate(MainActivity.java:17)
       at android.app.Activity.performCreate(Activity.java:6876)
       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135)
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3206)
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349) 
       at android.app.ActivityThread.access$1100(ActivityThread.java:221) 
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794) 
       at android.os.Handler.dispatchMessage(Handler.java:102) 
       at android.os.Looper.loop(Looper.java:158) 
       at android.app.ActivityThread.main(ActivityThread.java:7224) 
       at java.lang.reflect.Method.invoke(Native Method) 
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
    Caused by: android.view.InflateException: Binary XML file line #14: Error inflating class fragment
       at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:794)
       at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:716)
       at android.view.LayoutInflater.rInflate(LayoutInflater.java:847)
       at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:810)
       at android.view.LayoutInflater.inflate(LayoutInflater.java:527)
       at android.view.LayoutInflater.inflate(LayoutInflater.java:429) 
       at android.view.LayoutInflater.inflate(LayoutInflater.java:380) 
       at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:284) 
       at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140) 
       at com.example.frank.listview_test.MainActivity.onCreate(MainActivity.java:17) 
       at android.app.Activity.performCreate(Activity.java:6876) 
       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135) 
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3206) 
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349) 
       at android.app.ActivityThread.access$1100(ActivityThread.java:221) 
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794) 
       at android.os.Handler.dispatchMessage(Handler.java:102) 
       at android.os.Looper.loop(Looper.java:158) 
       at android.app.ActivityThread.main(ActivityThread.java:7224) 
       at java.lang.reflect.Method.invoke(Native Method) 
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
       at com.example.frank.listview_test.MainActivity$TestListFragment.onCreateView(MainActivity.java:37)
       at android.app.Fragment.performCreateView(Fragment.java:2281)
       at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:954)
       at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1141)
       at android.app.FragmentManagerImpl.addFragment(FragmentManager.java:1245)
       at android.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2218)
       at android.app.FragmentController.onCreateView(FragmentController.java:98)
       at android.app.Activity.onCreateView(Activity.java:6070)
       at android.support.v4.app.BaseFragmentActivityHoneycomb.onCreateView(BaseFragmentActivityHoneycomb.java:36)
       at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:75)
       at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:766)
       at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:716) 
       at android.view.LayoutInflater.rInflate(LayoutInflater.java:847) 
       at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:810) 
       at android.view.LayoutInflater.inflate(LayoutInflater.java:527) 
       at android.view.LayoutInflater.inflate(LayoutInflater.java:429) 
       at android.view.LayoutInflater.inflate(LayoutInflater.java:380) 
       at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:284) 
       at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140) 
       at com.example.frank.listview_test.MainActivity.onCreate(MainActivity.java:17) 
       at android.app.Activity.performCreate(Activity.java:6876) 
       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135) 
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3206) 
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349) 
       at android.app.ActivityThread.access$1100(ActivityThread.java:221) 
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794) 
       at android.os.Handler.dispatchMessage(Handler.java:102) 
       at android.os.Looper.loop(Looper.java:158) 
       at android.app.ActivityThread.main(ActivityThread.java:7224) 
       at java.lang.reflect.Method.invoke(Native Method) 
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

这是我的相关代码...

activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:background="#FFFFFF"
    android:gravity="center"
    tools:context="com.example.frank.listview_test.MainActivity">

    <fragment android:name="com.example.frank.listview_test.MainActivity$TestListFragment"
        android:id="@+id/list"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</FrameLayout>

list_fragment.xml：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/listFragment"
    android:layout_width="match_parent" android:layout_height="match_parent">

    <ListView
        android:id="@+id/testListView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center" />

</FrameLayout>

list_item.xml：

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="70dp"
    android:textSize="50sp"
    android:textColor="#000000"
    android:layout_gravity="center"/>

MainActivity.java：

package com.example.frank.listview_test;

import android.app.Fragment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    public static class TestListFragment extends Fragment {

        private String[] myStringArray = new String[20];
        private ListView listView;

        private void setArray() {
            for (int i = 0; i < 10; i++) {
                this.myStringArray[i] = "hello";
            }
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            setArray();

            ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(),R.layout.list_item , myStringArray);
            listView = (ListView) getActivity().findViewById(R.id.testListView);
            listView.setAdapter(adapter);

            // Inflate the layout for this fragment
            return inflater.inflate(R.layout.list_fragment, container, false);
        }
    }
}

此代码中是否有任何明显的错误可能导致此错误？

【问题讨论】：

标签： android xml android-layout listview android-fragments

【解决方案1】：

您的片段代码onCreateView() 应该首先扩充包含ListView 的list_fragment 布局。那么你应该在膨胀的布局上而不是在活动上调用findViewById()，因为片段布局还不是活动视图层次结构的一部分。

例如：

// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.list_fragment, container, false);
listView = (ListView) view.findViewById(R.id.testListView);
listView.setAdapter(adapter);

return view;

【讨论】：

太棒了。那行得通。所以，我的下一个问题是，如果你不介意，你什么时候会在 Fragment 类的活动中调用findViewById()？有没有在片段类中使用getActivity().findViewById 的情况？
几乎没有。从设计的角度来看，片段应该独立于其托管活动，并且不关心活动的特定细节，例如层次结构中的其他视图。为了让片段找到自己的视图，最好将其限制为您在onCreateView() 中创建的片段自己的视图子树，以便以后访问例如getView().

【解决方案2】：

试试这个：

View view = inflater.inflate(R.layout.list_fragment, container, false);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(),R.layout.list_item , myStringArray);
            listView = (ListView) view.findViewById(R.id.testListView);
            listView.setAdapter(adapter);
return view;

【讨论】：

【解决方案3】：

当我们要在运行时在活动上加载片段时，可能会发生此错误。所以，代码模式就像，

共有三个文件： 1. MainActivity.java 2. WelcomeFragment.java 3.LoginFragment.java

MainActivity.java

FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

    WelcomeFragment f1 = new WelcomeFragment();
    fragmentTransaction.replace(R.id.fragmentContainer, f1);
    fragmentTransaction.addToBackStack(null);
    fragmentTransaction.commit();

WelcomeFragment.java

public class WelcomeFragment extends Fragment {
    Button btnLogin;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.layout_fragment_welcome, container, false);
        return view;
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        btnLogin = view.findViewById(R.id.btnLogin);
        btnLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                FragmentManager fragmentManager = getFragmentManager();
                LoginFragment f2 = new LoginFragment();
                FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
                fragmentTransaction.replace(R.id.fragmentContainer, f2);
                fragmentTransaction.addToBackStack(null);
                fragmentTransaction.commit();
            }
        });
    }
}

【讨论】：