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Android：在Fragment中动态添加TextView-保持空值null引用

[英]Android: Adding TextView dynamically in Fragment - keep gettin null reference

 原文  2017-03-15 15:34:25  8   3    java/ android/ android-fragments

问题描述

I'm new to developing for Android and I'm trying to add TextView object to a fragment layout dynamically, however I keep getting this null reference error: 我是Android开发新手，正在尝试将TextView对象动态添加到片段布局，但是我不断收到此null引用错误： 

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.takemeout/com.takemeout.android.event.EventOverviewActivity}: android.view.InflateException: Binary XML file line #16: Binary XML file line #16: Error inflating class fragment
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
                                                                       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                                                                       at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                                                                       at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                       at android.os.Looper.loop(Looper.java:154)
                                                                       at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                       at java.lang.reflect.Method.invoke(Native Method)
                                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                                                                    Caused by: android.view.InflateException: Binary XML file line #16: Binary XML file line #16: Error inflating class fragment
                                                                    Caused by: android.view.InflateException: Binary XML file line #16: Error inflating class fragment
                                                                    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.LinearLayout.addView(android.view.View)' on a null object reference
                                                                       at com.takemeout.android.event.EventListFragment.onCreateView(EventListFragment.java:36)
                                                                       at android.support.v4.app.Fragment.performCreateView(Fragment.java:2189)
                                                                       at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1255)
                                                                       at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1472)
                                                                       at android.support.v4.app.FragmentManagerImpl.addFragment(FragmentManager.java:1691)
                                                                       at android.support.v4.app.FragmentManagerImpl.onCreateView(FragmentManager.java:3413)
                                                                       at android.support.v4.app.FragmentController.onCreateView(FragmentController.java:120)
                                                                       at android.support.v4.app.FragmentActivity.dispatchFragmentsOnCreateView(FragmentActivity.java:378)
                                                                       at android.support.v4.app.BaseFragmentActivityHoneycomb.onCreateView(BaseFragmentActivityHoneycomb.java:33)
                                                                       at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:79)
                                                                       at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:777)
                                                                       at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:727)
                                                                       at android.view.LayoutInflater.rInflate(LayoutInflater.java:858)
                                                                       at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:821)
                                                                       at android.view.LayoutInflater.inflate(LayoutInflater.java:518)
                                                                       at android.view.LayoutInflater.inflate(LayoutInflater.java:426)
                                                                       at android.view.LayoutInflater.inflate(LayoutInflater.java:377)
                                                                       at com.android.internal.policy.PhoneWindow.setContentView(PhoneWindow.java:412)
                                                                       at android.app.Activity.setContentView(Activity.java:2414)
                                                                       at com.takemeout.android.event.EventOverviewActivity.onCreate(EventOverviewActivity.java:33)
                                                                       at android.app.Activity.performCreate(Activity.java:6679)
                                                                       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
                                                                       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
                                                                       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                                                                       at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                                                                       at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                       at android.os.Looper.loop(Looper.java:154)
                                                                       at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                       at java.lang.reflect.Method.invoke(Native Method)
                                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

I'm unsure as of how to initialise the TextView object in onCreateView, as everything I've tried has produced this same message. 我不确定如何在onCreateView中初始化TextView对象，因为我尝试过的一切都产生了相同的消息。 Here is my code: 这是我的代码： 

package com.takemeout.android.event;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup; 
import android.widget.LinearLayout;
import android.widget.TextView;

import com.takemeout.android.R;

import java.util.Calendar;
import java.util.List;



public class EventListFragment extends Fragment {

  EventOverviewProvider provider = new EventOverviewProvider();
  List<EventOverviewProjection> eventsToday = provider.getTodayEvents();


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

    View v = inflater.inflate(R.layout.fragment_event_list, container, false);
    //getEventsToday(eventsToday, v);
    LinearLayout ll = (LinearLayout) v.findViewById(R.id.fragment_event_list);

    TextView text = new TextView(this.getActivity());
    text.setText("Sample text");
    ll.addView(text);


    // Inflate the layout for this fragment
    return v;
 }

 @Override
 public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
 }



 }

Here is my fragment_event_list.xml: 这是我的fragment_event_list.xml： 

   <?xml version="1.0" encoding="utf-8"?>
   <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
       xmlns:app="http://schemas.android.com/apk/res-auto"
       android:orientation="vertical" android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:weightSum="1">


   </LinearLayout>

Anyone have an idea of what I might be doing wrong? 有人知道我可能做错了什么吗？

3 个解决方案

解决方案1
 3  2017-03-15 15:42:43

Your LinearLayout is missing id. 您的LinearLayout缺少ID。 Just add android:id="@+id/fragment_event_list to LinearLayout in your xml. But you should choose a better name, something like @+id/list_view 只需在xml中将android:id="@+id/fragment_event_list到LinearLayout中即可。但是您应该选择一个更好的名称，例如@+id/list_view

解决方案2
 2 已采纳  2017-03-15 15:42:12

Add the ID: in Xml 在Xml中添加ID： 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/fragment_event_list"    //add this
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:weightSum="1">


</LinearLayout>

The ID is not added properly. 该ID未正确添加。 That's why it gives null. 这就是为什么它给出null的原因。

解决方案3
 0  2017-03-15 15:47:47

Update your onCreateView method to : 将您的onCreateView方法更新为： 

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

View v = inflater.inflate(R.layout.fragment_event_list, container, false);
//getEventsToday(eventsToday, v);
LinearLayout ll = (LinearLayout) v;

TextView text = new TextView(this.getActivity());
text.setText("Sample text");
ll.addView(text);


// Inflate the layout for this fragment
return v;
}

since your parent layout itself is the layout you want to use to add textView , you can just typecast it and you are good to go. 由于父layout本身就是您要用于添加textView的layout ，因此您可以进行typecast ，然后就可以使用了。

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