Android使用Fragment，不能得到Fragment内部控件，findViewById()结果是Null

intergameover 2014-06-04 02:38:28

程序非常简单，好长时间没有搞定，郁闷。。。。。。。。。。。。
描述：
一个Activity：MainActivity，内部是一个Fragment：FragmentA，FragmentA里面有TextView。
问题：无论如何也得不到FragmentA内部的TextView，返回值永远是Null
具体描述：
MainActivity的layout：activity_main.xml

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

  

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  

    android:orientation="horizontal"  

    android:layout_width="match_parent"  

    android:layout_height="match_parent">  

  

    <fragment android:name="com.fragmentexercise.FragmentA"  

              android:id="@+id/fragment_a"  

              android:layout_width="match_parent"  

              android:layout_height="match_parent" />  

</LinearLayout>

FragmentA的layout：fragment_a.xml

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

  

<TextView xmlns:android="http://schemas.android.com/apk/res/android"  

    android:id="@+id/textView1"  

    android:layout_width="match_parent"  

    android:layout_height="match_parent"  

    android:padding="16dp"  

    android:textSize="18sp"  

    android:text="初始化文本" />

MainActivity.java

public class MainActivity extends Activity {  

  

    @Override  

    protected void onCreate(Bundle savedInstanceState) {  

        super.onCreate(savedInstanceState);  

        setContentView(R.layout.activity_main);  

  

    }

FragmentA.java

public class FragmentA extends Fragment {  

  

    @Override  

    public View onCreateView(LayoutInflater inflater, ViewGroup container,  

            Bundle savedInstanceState) {  

        return inflater.inflate(R.layout.fragment_a, container, false);  

    }  

      

    @Override  

    public void onActivityCreated(Bundle savedInstanceState) {  

        super.onActivityCreated(savedInstanceState);  

//      TextView textView1 = (TextView) getView().findViewById(R.id.textView1);  

//      textView1.setText("改变");  

    }

具体问题：
在FragmentA.onActivityCreated()中，
TextView textView1 = (TextView) getView().findViewById(R.id.textView1); 得到的始终是Null。

在Fragment.onCreateView()中，
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) { 第二个参数 container一直是个空值

在MainActivity中，findViewById（R.id.textView1), 同样是空值。

问题在哪里呢？？？？？？？？？？

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0 and 1 2015-10-07

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这个问题你是怎么解决的？没看太懂

AnitaLoveJava 2015-09-21

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引用 5 楼 birdsaction 的回复:

哦。这个我到没测试，我都是习惯在 onCreateView 里面把所有的view找到。这样做。

   
 private View view;
 private TextView textView1 ;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
         view = inflater.inflate(R.layout.fragment_a, container, false);
         if (view == null) {
            Log.i("FragmentA", " onCreateView:view is null");
        } else {
            Log.i("FragmentA", "onCreateView:view is NOOOOOOOOOOOOOOOOT null");
        }
         textView1 = (TextView) view.findViewById(R.id.textView1);
         return view;
    }

鼓捣了一天终于解决了，虽然还是和API上的例子不同，也不知道为什么API上的例子就能找到，我和例子写的一模一样就是死活空指针，郁闷死我了，看来只能这样解决了，谢谢

intergameover 2014-06-04

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引用 6 楼 u010110521 的回复:

试试继承FragmentActivity

这样就成功了，在FragmentA的onStart等方法中，getActivity().findViewById(R.id.textView1) 就能得到这个TextView。直接继承 android.app.Fragment，就不行。也许是Android的bug吧。其实我是按照developer.android.com上的trainning的例子做的，那个例子是为了兼容android3.0以前的系统，继承了android.support.v4.app.Fragment，官方例子运行正常。我的手机是Android4.1的，可以支持Fragment，所以我直接继承了adnroid.app.Fragment，结果就死活不成功。想不到是这个原因。谢谢各位。结贴。

intergameover 2014-06-04

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引用 5 楼 birdsaction 的回复:

哦。这个我到没测试，我都是习惯在 onCreateView 里面把所有的view找到。这样做。

   
 private View view;
 private TextView textView1 ;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
         view = inflater.inflate(R.layout.fragment_a, container, false);
         if (view == null) {
            Log.i("FragmentA", " onCreateView:view is null");
        } else {
            Log.i("FragmentA", "onCreateView:view is NOOOOOOOOOOOOOOOOT null");
        }
         textView1 = (TextView) view.findViewById(R.id.textView1);
         return view;
    }

实践过，这样做确实可以。

wangdong20 2014-06-04

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先Inflate你的fragment布局，然后再用inflate fragment的View调用findViewById()查找

u010110521 2014-06-04

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试试继承FragmentActivity

Birds2018 2014-06-04

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哦。这个我到没测试，我都是习惯在 onCreateView 里面把所有的view找到。这样做。

   
 private View view;
 private TextView textView1 ;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
         view = inflater.inflate(R.layout.fragment_a, container, false);
         if (view == null) {
            Log.i("FragmentA", " onCreateView:view is null");
        } else {
            Log.i("FragmentA", "onCreateView:view is NOOOOOOOOOOOOOOOOT null");
        }
         textView1 = (TextView) view.findViewById(R.id.textView1);
         return view;
    }

intergameover 2014-06-04

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@birdsaction，用了你的办法，onCreateView中，可以产生view。但是在onActivityCreated中，view.findViewById(R.id.textView1),还是空。

public class FragmentA extends Fragment {
	private View view;
	@Override
	public View onCreateView(LayoutInflater inflater, ViewGroup container,
			Bundle savedInstanceState) {
		 view = inflater.inflate(R.layout.fragment_a, container, false);
		 if (view == null) {
			Log.i("FragmentA", " onCreateView:view is null");
		} else {
			Log.i("FragmentA", "onCreateView:view is NOOOOOOOOOOOOOOOOT null");
		}
		 return view;
	}
	
	@Override
	public void onActivityCreated(Bundle savedInstanceState) {
		super.onActivityCreated(savedInstanceState);
		if (view == null) {
			Log.i("FragmentA", " onActivityCreated:view is null");
		} else {
			Log.i("FragmentA", "onActivityCreated:view is NOOOOOOOOOOOOOOOOT null");
		}
		TextView textView1 = (TextView) view.findViewById(R.id.textView1);
		if (textView1 == null) {
			Log.i("FragmentA", " onActivityCreated:textView1 is null");
		} else {
			Log.i("FragmentA", "onActivityCreated:textView1 is NOOOOOOOOOOOOOOOOT null");
		}
		//textView1.setText("改变");
	}
}

logcat：

06-04 16:56:26.953: D/ActivityThread(22471): setTargetHeapUtilization:0.25
06-04 16:56:26.953: D/ActivityThread(22471): setTargetHeapIdealFree:8388608
06-04 16:56:26.953: D/ActivityThread(22471): setTargetHeapConcurrentStart:2097152
06-04 16:56:27.314: W/IconCustomizer(22471): can't load transform_config.xml
06-04 16:56:27.344: I/FragmentA(22471): onCreateView:view is NOOOOOOOOOOOOOOOOT null
06-04 16:56:27.344: I/FragmentA(22471): onActivityCreated:view is NOOOOOOOOOOOOOOOOT null
06-04 16:56:27.344: I/FragmentA(22471):  onActivityCreated:textView1 is null
06-04 16:56:27.404: I/Adreno200-EGL(22471): <qeglDrvAPI_eglInitialize:294>: EGL 1.4 QUALCOMM build:  (CL3090659)
06-04 16:56:27.404: I/Adreno200-EGL(22471): Build Date: 09/03/13 Tue
06-04 16:56:27.404: I/Adreno200-EGL(22471): Local Branch: 
06-04 16:56:27.404: I/Adreno200-EGL(22471): Remote Branch: 
06-04 16:56:27.404: I/Adreno200-EGL(22471): Local Patches: 
06-04 16:56:27.404: I/Adreno200-EGL(22471): Reconstruct Branch:

映映 2014-06-04

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mView = inflater.inflate(R.layout.ui_listview, null); 用mView查找

Birds2018 2014-06-04

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@Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); TextView textView1 = (TextView) view.findViewById(R.id.textView1); //引用上面创建好的。就可以了，刚忘了修改 textView1.setText("改变"); }

Birds2018 2014-06-04

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这样就可以了。


public class FragmentA extends Fragment {  

    private View view;   

    @Override  
    public View onCreateView(LayoutInflater inflater, ViewGroup container,  
            Bundle savedInstanceState) {  
       view =  inflater.inflate(R.layout.fragment_a, container, false);  
        return view ;
    }  
       
    @Override  
    public void onActivityCreated(Bundle savedInstanceState) {  
        super.onActivityCreated(savedInstanceState);  
     TextView textView1 = (TextView) getView().findViewById(R.id.textView1);  
      textView1.setText("改变");  
    }