android自定义列表适配器不显示项目

Question

我正在使用 fragment 来显示我发现的所有对等点，它成功到达 fragment 但在尝试显示对等点时崩溃。

fragment

    public class peerItemFragment extends ListFragment {

        private List<WifiP2pDevice> peers = new ArrayList<>();
        ProgressDialog progressDialog = null;
        View mContentView = null;
        private WifiP2pDevice device;

        @Override
        public void onActivityCreated(Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);
            this.setListAdapter(new WiFiPeerListAdapter(getActivity(), R.layout.row_devices, peers));
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            mContentView = inflater.inflate(R.layout.fragment_item_grid, null);
            return mContentView;
        }

        /**
         * @return this device
         */
        public WifiP2pDevice getDevice() {
            return device;
        }

        private static String getDeviceStatus(int deviceStatus) {
            Log.d(sendActivity.TAG, "Peer status :" + deviceStatus);
            switch (deviceStatus) {
                case WifiP2pDevice.AVAILABLE:
                    return "Available";
                case WifiP2pDevice.INVITED:
                    return "Invited";
                case WifiP2pDevice.CONNECTED:
                    return "Connected";
                case WifiP2pDevice.FAILED:
                    return "Failed";
                case WifiP2pDevice.UNAVAILABLE:
                    return "Unavailable";
                default:
                    return "Unknown";
            }
        }

        /**
         * Initiate a connection with the peer.
         */
        @Override
        public void onListItemClick(ListView l, View v, int position, long id) {
            WifiP2pDevice device = (WifiP2pDevice) getListAdapter().getItem(position);
            ((DeviceActionListener) getActivity()).showDetails(device);
        }

        /**
         * Array adapter for ListFragment that maintains WifiP2pDevice list.
         */
        private class WiFiPeerListAdapter extends ArrayAdapter<WifiP2pDevice> {

            private List<WifiP2pDevice> items;

            /**
             * @param context
             * @param textViewResourceId
             * @param objects
             */
            public WiFiPeerListAdapter(Context context, int textViewResourceId,
                                       List<WifiP2pDevice> objects) {
                super(context, textViewResourceId, objects);
                items = objects;

            }

            @Override
            public View getView(int position, View convertView, ViewGroup parent) {
                View v = convertView;
                if (v == null) {
                    LayoutInflater vi = (LayoutInflater) getActivity().getSystemService(
                            Context.LAYOUT_INFLATER_SERVICE);
                    v = vi.inflate(R.layout.row_devices, parent, false);
                }
                WifiP2pDevice device = items.get(position);
                if (device != null) {
                    TextView top = (TextView) v.findViewById(R.id.device_name);
                    TextView bottom = (TextView) v.findViewById(R.id.device_details);
                    if (top != null) {
                        top.setText(device.deviceName);
                    }
                    if (bottom != null) {
                        bottom.setText(getDeviceStatus(device.status));
                    }
                }
                return v;
            }
        }

        /**
         * Update UI for this device.
         *
         * @param device WifiP2pDevice object
         */
        public void updateThisDevice(WifiP2pDevice device) {
            this.device = device;
            TextView view = (TextView) mContentView.findViewById(R.id.tvMyName);
            view.setText(device.deviceName);
            view = (TextView) mContentView.findViewById(R.id.tvMyStatus);
            view.setText(getDeviceStatus(device.status));
        }


        public void addPeers(WifiP2pDeviceList peerList) {
            if (progressDialog != null && progressDialog.isShowing()) {
                progressDialog.dismiss();
            }

            peers.clear();
            peers.addAll(peerList.getDeviceList());
            ((WiFiPeerListAdapter) getListAdapter()).notifyDataSetChanged();

            if (peers.size() == 0) {
                Log.d(sendActivity.TAG, "No devices found");
                return;
            }
        }

        public void clearPeers() {
            peers.clear();
            ((WiFiPeerListAdapter) getListAdapter()).notifyDataSetChanged();
        }

问题 atm 是当我从主类调用时使用以下代码调用它时...

            peerItemFragment peerFragment = new peerItemFragment();

        FragmentManager managerAuthenticate = getFragmentManager();

        FragmentTransaction transactionAuthen = managerAuthenticate.beginTransaction();

        // Replace whatever is in the fragment_container view with this fragment,
        // and add the transaction to the back stack so the user can navigate back
        transactionAuthen.replace(R.id.fragment_container, peerFragment);
        transactionAuthen.addToBackStack(null);


//***************************************************
        Bundle bundle = new Bundle();
        bundle.putParcelableArrayList("list", mService.peerList);
        peerFragment.setArguments(bundle);

        // Commit the transaction
        transactionAuthen.commit();

逐步查看并运行它后，我发现以下行有问题？

    ((WiFiPeerListAdapter) getListAdapter()).notifyDataSetChanged();

真的很奇怪，因为这都是从谷歌样本中提取的，不知道为什么会崩溃..

另请注意，该 fragment 有一个 listView 命名列表，如 google 所建议的那样(没有问题)。

很难发现哪里出了问题？会不会是适配器不在？

编辑---------------------------------------- --------------------------

从 Activity 调用 fragment

        peerItemFragment peerFragment = new peerItemFragment();

    FragmentManager managerAuthenticate = getFragmentManager();

    Bundle bundle = new Bundle();
    ArrayList<WifiP2pDevice> list = new ArrayList<>(mService.peerList.getDeviceList());
    bundle.putParcelableArrayList("list", list);

    peerFragment.setArguments(bundle);

    FragmentTransaction transactionAuthen = managerAuthenticate.beginTransaction();

    // Replace whatever is in the fragment_container view with this fragment,
    // and add the transaction to the back stack so the user can navigate back
    transactionAuthen.replace(R.id.fragment_container, peerFragment);
    transactionAuthen.addToBackStack(null);

    // Commit the transaction
    transactionAuthen.commit();

    //pass peer list to fragment to display
    //peerFragment.addPeers(mService.peerList);

}

编辑后的 fragment

public class peerItemFragment extends ListFragment {

private List<WifiP2pDevice> peers = new ArrayList<>();
ProgressDialog progressDialog = null;
View mContentView = null;
private WifiP2pDevice device;

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    this.setListAdapter(new WiFiPeerListAdapter(getActivity(), R.layout.row_devices, peers));

    Bundle bundle = getArguments();

    peers = bundle.getParcelableArrayList("list");

    ((WiFiPeerListAdapter) getListAdapter()).notifyDataSetChanged();

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    mContentView = inflater.inflate(R.layout.fragment_item_grid, null);
    return mContentView;
}

/**
 * @return this device
 */
public WifiP2pDevice getDevice() {
    return device;
}

private static String getDeviceStatus(int deviceStatus) {
    Log.d(sendActivity.TAG, "Peer status :" + deviceStatus);
    switch (deviceStatus) {
        case WifiP2pDevice.AVAILABLE:
            return "Available";
        case WifiP2pDevice.INVITED:
            return "Invited";
        case WifiP2pDevice.CONNECTED:
            return "Connected";
        case WifiP2pDevice.FAILED:
            return "Failed";
        case WifiP2pDevice.UNAVAILABLE:
            return "Unavailable";
        default:
            return "Unknown";
    }
}

/**
 * Initiate a connection with the peer.
 */
@Override
public void onListItemClick(ListView l, View v, int position, long id) {
    WifiP2pDevice device = (WifiP2pDevice) getListAdapter().getItem(position);
    ((DeviceActionListener) getActivity()).showDetails(device);
}

/**
 * Array adapter for ListFragment that maintains WifiP2pDevice list.
 */
private class WiFiPeerListAdapter extends ArrayAdapter<WifiP2pDevice> {

    private List<WifiP2pDevice> items;

    /**
     * @param context
     * @param textViewResourceId
     * @param objects
     */
    public WiFiPeerListAdapter(Context context, int textViewResourceId,
                               List<WifiP2pDevice> objects) {
        super(context, textViewResourceId, objects);
        items = objects;

    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View v = convertView;
        if (v == null) {
            LayoutInflater vi = (LayoutInflater) getActivity().getSystemService(
                    Context.LAYOUT_INFLATER_SERVICE);
            v = vi.inflate(R.layout.row_devices, parent, false);
        }
        WifiP2pDevice device = items.get(position);
        if (device != null) {
            TextView top = (TextView) v.findViewById(R.id.device_name);
            TextView bottom = (TextView) v.findViewById(R.id.device_details);
            if (top != null) {
                top.setText(device.deviceName);
            }
            if (bottom != null) {
                bottom.setText(getDeviceStatus(device.status));
            }
        }
        return v;
    }
}

Answer 1

您的代码的问题在于，当您调用 addPears 时，onActivityCreated 可能尚未被调用(事务未以同步方式执行)，导致 getListAdapter 返回 null。要修复它，您可以在 bundle 中添加您的 peerList，(WifiP2pDevice 是 parcelable)，然后设置这个作为 arguments 你的 Fragment

Bundle bundle = new Bundle();
ArrayList<WifiP2pDevice> list = new ArrayList<>(mService.peerList.getDeviceList());
bundle.putParcelableArrayList("list", list);
peerFragmet.setArguments(bundle);

并摆脱

peerFragment.addPeers(mService.peerList);

当 onActivityCreated 被调用时，您可以使用 getArguments 读取 bundle ，检索您的 peerList 对象并实例化您的适配器