访问片段中的视图

Question

如果我从它的Java代码中使用textview。所以我假设我在某个地方犯了一个错误。任何人都可以看到问题吗？

package com.projectcaruso.naturalfamilyplaning; 

import com.projectcaruso.naturalfamilyplanning.R; 
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.TextView; 


public class HistoryFragment extends Fragment { 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 

     super.onCreate(savedInstanceState); 
     SQLHelper entry = new SQLHelper(getActivity()); 

     TextView tv = (TextView) getView().findViewById(R.id.tvSQLinfo); 

     entry.open(); 
     String results = entry.getData(); 
     entry.close(); 

     tv.setText(results); 

    }  

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

} 

XML：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:orientation ="vertical" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" > 

    <TableLayout 
     android:layout_width="fill_parent" 
     android:layout_height="fill_parent"> 

     <TableRow> 

      <TextView 
       android:layout_width="fill_parent" 
       android:layout_height="fill_parent" 
       android:text="date" /> 

      <TextView 
       android:layout_width="fill_parent" 
       android:layout_height="fill_parent" 
       android:text="temp" /> 

     </TableRow> 
    </TableLayout> 

    <TextView 
     android:id="@+id/tvSQLinfo" 
     android:layout_width="fill_parent" 
     android:layout_height="fill_parent" 
     android:text="Get info from db" /> 
</LinearLayout> 

的logcat：

05-12 22:55:01.799: E/AndroidRuntime(1983): FATAL EXCEPTION: main 
05-12 22:55:01.799: E/AndroidRuntime(1983): java.lang.NullPointerException 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at com.projectcaruso.naturalfamilyplaning.HistoryFragment.onCreate(HistoryFragment.java:20) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at android.support.v4.app.Fragment.performCreate(Fragment.java:1437) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:877) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1444) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:429) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at android.os.Handler.handleCallback(Handler.java:725) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at android.os.Handler.dispatchMessage(Handler.java:92) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at android.os.Looper.loop(Looper.java:137) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at android.app.ActivityThread.main(ActivityThread.java:5041) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at java.lang.reflect.Method.invoke(Method.java:511) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
05-12 22:55:01.799: E/AndroidRuntime(1983):  at dalvik.system.NativeStart.main(Native Method) 

Answer 1

的问题是，您的来电getView()回报null。

这是为什么？
因为onCreate()在onCreateView()之前被调用。

看一看的片段生命周期的更多信息：http://developer.android.com/guide/components/fragments.html#Creating

解决方案：
也 移动你的逻辑到onCreateView()方法，并保持参照放大的视图，而不是通过getView()调用它。 它看起来像这样：

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

    SQLHelper entry = new SQLHelper(getActivity()); 
    entry.open(); 
    String results = entry.getData(); 
    entry.close(); 

    TextView tv = (TextView) view.findViewById(R.id.tvSQLinfo); 
    tv.setText(results); 

    return view; 
}