java - 类转换异常 : MainActivity cannot be cast to Listener

Question

我正在尝试为我的 ScanFragment 实现 WifiScanner 监听器，但我收到此错误:java.lang.ClassCastException: emilsoft.wifitest3.MainActivity cannot be cast to emilsoft.wifitest3.WifiScanner$Listener我已经用普通的 Activities 做到了这一点，现在我正在尝试将它转换为 Fragments，我目前正在了解它们。我做了很多研究，但找不到可行的解决方案。有错误的代码我已经注释掉了

所以我的主要 Activity :

private SectionsPagerAdapter mSectionsPagerAdapter;
private ViewPager mViewPager;

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

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    // Create the adapter that will return a fragment for each of the three
    // primary sections of the activity.
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.container);
    mViewPager.setAdapter(mSectionsPagerAdapter);

    TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
    tabLayout.setupWithViewPager(mViewPager);

}

我的SectionsPagerAdapter 类:

public class SectionsPagerAdapter extends FragmentPagerAdapter{

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

@Override
public Fragment getItem(int position) {
    switch (position) {
        case 0: return ScanFragment.newInstance();
    }
    return null;
}

我的ScanFragment:

public class ScanFragment extends Fragment implements WifiScanner.Listener {
   private ScanCollector sc;
   private WifiManager wifi;
   public ScanFragment() {}

    public static ScanFragment newInstance() {
        return new ScanFragment();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View result = inflater.inflate(R.layout.fragment_scan_results, container, false);
        wifi = (WifiManager) getActivity().getSystemService(Context.WIFI_SERVICE);
        sc = new ScanCollector(this.getContext()); //THE ERROR STARTS HERE
        return result;
    }

我的ScanCollector 类(处理添加到 WifiScanner 类的监听器):

public class ScanCollector {

// The context wrapper that we'll use for accessing system services, receiving
// broadcasts from the WifiManager
private final Context context;

private WifiScanner.Listener listener;

public ScanCollector(Context context) {
    if (context == null)
        throw new NullPointerException();
    this.context = context;
    this.listener = (WifiScanner.Listener)context; //THE ERROR IS HERE
}

问题是我无法将正确的上下文传递给我的 ScanCollector 类，该类随后会将其转换为 WifiScanner.Listener。可能是一个非常愚蠢的解决方案，但我找不到它。

提前致谢!

Answer 1

一个是上下文，另一个是WifiScanner.Listener。您的 ScanCollector 需要两者，所以传递它们:

public ScanCollector(Context context, WifiScanner.Listener listener) {
    if (context == null)
        throw new NullPointerException();
    this.context = context;
    this.listener = listener
}

当你创建它时:

sc = new ScanCollector(getActivity(), this);