1

我正在尝试使用片段创建对话框，但是当我调用 setAdapter 方法时，我有一个 Java NullPointerException，我找不到错误。

Java 代码：

public class MainActivity extends FragmentActivity {

Context myContext;

private MyAdapter mAdapter;
private ViewPager mPager;

String TAG = "Dialog";

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

            myContext = this;

    findViewById(R.id.button1).setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            final Dialog dialog = new Dialog(myContext);

            dialog.setContentView(R.layout.layout_dialog);

            mAdapter = new MyAdapter(getSupportFragmentManager()); 

            mPager = (ViewPager) dialog.findViewById(R.id.myViewPager);
            **mPager.setAdapter(mAdapter);** //Line 39, the error is on this line.

            dialog.show();
        }
    });
}

public class MyAdapter extends FragmentPagerAdapter {
    int counts;

    public MyAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public int getCount() {
        return 3;
    }

    @Override
    public Fragment getItem(int position) {
        switch (position) {
        case 0:
            return new ImageFragment(R.drawable.icecream);

        case 1:
            return new ImageFragment(R.drawable.cupcake);

        case 2:
            return new ImageFragment(R.drawable.donut);

        default:
            return null;
        }

    }
}
}

片段类：

public class ImageFragment extends Fragment {

private final int imageResourceId;

public ImageFragment(int imageResourceId) {
    this.imageResourceId = imageResourceId;
}

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

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

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.activity_dialog_item, container,
            false);
    ImageView imageView = (ImageView) view.findViewById(R.id.imageView1);
    imageView.setImageResource(imageResourceId);
    return view;
}

}

activity_main xml 代码：

<RelativeLayout 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">

<Button
    android:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentRight="true"
    android:layout_marginRight="20dip"
    android:layout_marginTop="30dip"
    android:text="Show Dialog" />

   </RelativeLayout>

layout_dialog.xml 代码：

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

<android.support.v4.view.ViewPager
    android:id="@+id/myViewPager"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

     </LinearLayout>

activity_dialog_item.xml 代码：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >

<ImageView
    android:id="@+id/imageView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerInParent="true"
    android:src="@drawable/cupcake" />

  </RelativeLayout>

错误：

03-06 13:58:22.546: E/AndroidRuntime(818): FATAL EXCEPTION: main
03-06 13:58:22.546: E/AndroidRuntime(818): java.lang.NullPointerException
03-06 13:58:22.546: E/AndroidRuntime(818):  at com.example.viewpager.MainActivity$1.onClick(MainActivity.java:39)
03-06 13:58:22.546: E/AndroidRuntime(818):  at android.view.View.performClick(View.java:2485)
03-06 13:58:22.546: E/AndroidRuntime(818):  at android.view.View$PerformClick.run(View.java:9080)
03-06 13:58:22.546: E/AndroidRuntime(818):  at android.os.Handler.handleCallback(Handler.java:587)
03-06 13:58:22.546: E/AndroidRuntime(818):  at android.os.Handler.dispatchMessage(Handler.java:92)
03-06 13:58:22.546: E/AndroidRuntime(818):  at android.os.Looper.loop(Looper.java:123)
03-06 13:58:22.546: E/AndroidRuntime(818):  at android.app.ActivityThread.main(ActivityThread.java:3683)
03-06 13:58:22.546: E/AndroidRuntime(818):  at java.lang.reflect.Method.invokeNative(Native Method)
03-06 13:58:22.546: E/AndroidRuntime(818):  at java.lang.reflect.Method.invoke(Method.java:507)
03-06 13:58:22.546: E/AndroidRuntime(818):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
03-06 13:58:22.546: E/AndroidRuntime(818):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-06 13:58:22.546: E/AndroidRuntime(818):  at dalvik.system.NativeStart.main(Native Method)
4

1 回答 1

0

编辑：

通过膨胀不是来自资源的视图来设置对话框的视图

    LayoutInflater inflatter= (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View v= inflatter.inflate(R.layout.layout_dialog);
dialog.setContentView(v);

在 onCreate 之前你不会得到上下文，

Context myContext = this;  // this throws you NPE,

尝试这样做

Context mycontext;

并在 onCreate

mycontext=this;
于 2013-03-06T09:08:42.367 回答