GridView中的一个片段崩溃

我跟着this tutorial创建了一个包含3个片段的布局，并使用ViewPager切换它们，它工作得很好。然后我尝试将GridView添加到中间片段中，以便它可以像this tutorial中显示的图像库那样执行，但我不断收到“不幸，**已停止”消息。在开始时我认为这可能是因为图像的大小太大而无法运行，所以我使用了第二个教程中的示例图像，但它不起作用。GridView中的一个片段崩溃

请帮助我，因为它困扰了我好几天。先谢谢你。：d

这是我的logcat：

java.lang.RuntimeException: Unable to start activity ComponentInfo{my.com.impressor.demo2/my.com.impressor.demo2.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.GridView.setAdapter(android.widget.ListAdapter)' on a null object reference 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.GridView.setAdapter(android.widget.ListAdapter)' on a null object reference 
at my.com.impressor.demo2.MainActivity.onCreate(MainActivity.java:27) 
at android.app.Activity.performCreate(Activity.java:6237) 
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107) 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

这是我的GridView中含有中间fragment.java：

public class Fragment2 extends Fragment { 

private GridView gridView; //added regarding to the answer by Atual in <http://stackoverflow.com/questions/22613064/using-gridview-image-in-fragment> 

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    View view = inflater.inflate(R.layout.fragment2, container, false); 
    GridView gridView = (GridView) view.findViewById(R.id.gridview); 
    gridView.setAdapter(new ImageAdapter(getActivity().getApplicationContext())); 
    return view; 
} 

}

这是相关的XML文件：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:background="@android:color/white" 
android:orientation="vertical" > 

<GridView xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@+id/gridview" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:columnWidth="90dp" 
    android:numColumns="auto_fit" 
    android:verticalSpacing="10dp" 
    android:horizontalSpacing="10dp" 
    android:stretchMode="columnWidth" 
    android:gravity="center" 
    />

Th是是在MainActivity：

public class MainActivity extends AppCompatActivity { 

//ImageView im; 

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

    GridView gridview = (GridView) findViewById(R.id.gridview); 
    gridview.setAdapter(new ImageAdapter(this)); 

    gridview.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
     public void onItemClick(AdapterView<?> parent, View v, 
           int position, long id) { 
      Toast.makeText(MainActivity.this, "" + position, 
        Toast.LENGTH_SHORT).show(); 
     } 
    }); 

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 

    TabLayout tabLayout = (TabLayout) findViewById(R.id.tab_layout); 
    tabLayout.addTab(tabLayout.newTab().setText("Service")); 
    tabLayout.addTab(tabLayout.newTab().setText("Gallery")); 
    tabLayout.addTab(tabLayout.newTab().setText("Contact Us")); 
    tabLayout.setTabGravity(TabLayout.GRAVITY_FILL); 

    final ViewPager viewPager = (ViewPager) findViewById(R.id.pager); 
    final PagerAdapter adapter = new PagerAdapter 
      (getSupportFragmentManager(), tabLayout.getTabCount()); 
    viewPager.setAdapter(adapter); 
    viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout)); 
    tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() { 
     @Override 
     public void onTabSelected(TabLayout.Tab tab) { 
      viewPager.setCurrentItem(tab.getPosition()); 
     } 

     @Override 
     public void onTabUnselected(TabLayout.Tab tab) { 

     } 

     @Override 
     public void onTabReselected(TabLayout.Tab tab) { 

     } 
    }); 
} 

/*public void biggerView(View v) 
{ 
    im=(ImageView)findViewById(R.id.selected); 

    switch (v.getId()) 
    { 
     case R.id.image1: im.setImageResource(R.drawable.p1); 
      break; 
     case R.id.image2: im.setImageResource(R.drawable.p2); 
      break; 
     case R.id.image3: im.setImageResource(R.drawable.p3); 
      break; 
     case R.id.image4: im.setImageResource(R.drawable.p4); 
      break; 
     case R.id.image5: im.setImageResource(R.drawable.p5); 
      break; 
     case R.id.image6: im.setImageResource(R.drawable.p6); 
      break; 
     case R.id.image7: im.setImageResource(R.drawable.p7); 
      break; 
    } 
}*/ 


@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    getMenuInflater().inflate(R.menu.menu_main, menu); 
    return true; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    int id = item.getItemId(); 
    if (id == R.id.action_settings) { 
     return true; 
    } 

    return super.onOptionsItemSelected(item); 
} 
}

这是ImageAdapter：

public class ImageAdapter extends BaseAdapter { 
private Context mContext; 

public ImageAdapter(Context c) { 
    mContext = c; 
} 

public int getCount() { 
    return mThumbIds.length; 
} 

public Object getItem(int position) { 
    return null; 
} 

public long getItemId(int position) { 
    return 0; 
} 

// create a new ImageView for each item referenced by the Adapter 
public View getView(int position, View convertView, ViewGroup parent) { 
    ImageView imageView; 
    if (convertView == null) { 
     // if it's not recycled, initialize some attributes 
     imageView = new ImageView(mContext); 
     imageView.setLayoutParams(new GridView.LayoutParams(85, 85)); 
     imageView.setScaleType(ImageView.ScaleType.CENTER_CROP); 
     imageView.setPadding(8, 8, 8, 8); 
    } else { 
     imageView = (ImageView) convertView; 
    } 

    imageView.setImageResource(mThumbIds[position]); 
    return imageView; 
} 

// references to our images 
private Integer[] mThumbIds = { 
     /*R.drawable.p1, R.drawable.p2, 
     R.drawable.p3, R.drawable.p4, 
     R.drawable.p5, R.drawable.p6, 
     R.drawable.p7, R.drawable.p8, 
     R.drawable.p9, R.drawable.p10, 
     R.drawable.p11, R.drawable.p12, 
     R.drawable.p13, R.drawable.p14, 
     R.drawable.p15, R.drawable.p16, 
     R.drawable.p17, R.drawable.p18, 
     R.drawable.p19, R.drawable.p20, 
     R.drawable.p21, R.drawable.p22, 
     R.drawable.p23*/ 
     R.drawable.sample_0, R.drawable.sample_1, 
     R.drawable.sample_2, R.drawable.sample_3, 
     R.drawable.sample_4, R.drawable.sample_5, 
     R.drawable.sample_6, R.drawable.sample_7 
}; 
}

来源

2016-01-21 plood

据我了解你的GridView位于你的片段（fragment2布局，而不是在activity_main）。所以你应该在Fragment中移动代码来处理它，因为在你的Activity中GridView不可用。 – thetonrifles

您正在'onCreateView'中调用'getActivity（）'，并且您正在访问此函数中的'GridView'，这可能会导致此问题。因为此时尚未创建getActivity。其次，请检查您在'acitivyt_main' xml –

中声明'GridView'突然发现gridView.setAdapter出现在fragment.java和MainActivity中，并且在MainActivity中的一个被删除后运行... – plood

你GridViewR.id.gridview似乎并不在布局R.layout.activity_main。将其添加到布局中，或者如果要使用片段，则加载片段，并且GridView应位于Fragment2布局R.layout.fragment2之内。

解决方案1 

如果您选择使用Fragment2然后下面的代码从MainActivity删除和添加内Fragment2

GridView gridview = (GridView) findViewById(R.id.gridview); 
gridview.setAdapter(new ImageAdapter(this)); 

gridview.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
    public void onItemClick(AdapterView<?> parent, View v, 
          int position, long id) { 
     Toast.makeText(MainActivity.this, "" + position, 
       Toast.LENGTH_SHORT).show(); 
    } 
});

解决方案2

如果您选择不使用Fragment2然后将以下代码添加到R.layout.activity_main

<GridView xmlns:android="http://schemas.android.com/apk/res/android" 
android:id="@+id/gridview" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:columnWidth="90dp" 
android:numColumns="auto_fit" 
android:verticalSpacing="10dp" 
android:horizontalSpacing="10dp" 
android:stretchMode="columnWidth" 
android:gravity="center" 
/>

其他建议

而且改变

public Object getItem(int position) { 
    return null; 
}

到

public Object getItem(int position) { 
    return mThumbIds[position]; 
}

来源

2016-01-21 13:43:09 Rohit5k2

感谢您的回复和建议！我可以问我是否通过在activity_main中添加GridView来选择solution2。它会显示GridView中的所有3个片段而不是fragment2吗？ – plood

取决于。如果您没有更改活动中的gridview部分并将其他片段加载到单独的容器中，则会显示在所有片段上。 – Rohit5k2

据我了解你的GridView位于您的片段（fragment2布局，而不是在activity_main）。所以你应该在Fragment中移动代码来处理它，因为在你的Activity中GridView不可用。

来源

2016-01-21 13:44:06 thetonrifles

谢谢你的回复！你是对的，我发现GridView的代码是在Fragment和MainActivity中。但我只是在片段中设置我的GridView。它可能会导致错误。 – plood

GridView中的一个片段崩溃

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