用于listView的setAdapter时出现NullPointerException

时间：2016-01-11 20:15:51

标签： android android-listview nullpointerexception viewstub

我被困在这条线上5天了。当我为它设置适配器时，你想帮助我为什么说Null Pointer Exception。

这是ListFileController 

public class ListFileController extends ArrayAdapter<Files> {
private Context context;
private int layoutId;
ArrayList<Files> array;

public ListFileController(Context context, int layoutId, ArrayList<Files> array) {
    super(context, layoutId, array);

    this.context = context;
    this.layoutId = layoutId;
    this.array = array;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    LayoutInflater inflater;
    View rowView = convertView;
    ViewHolder holder = null;
    if (rowView == null){
        holder = new ViewHolder();

        inflater = (LayoutInflater) context.getSystemService(context.LAYOUT_INFLATER_SERVICE);

        rowView = inflater.inflate(R.layout.list_file_layout, parent, false);
        holder.icon = (ImageView) rowView.findViewById(R.id.icon);
        holder.fileName = (TextView) rowView.findViewById(R.id.fileName);
        holder.size = (TextView) rowView.findViewById(R.id.fileSize);

        rowView.setTag(holder);
    }
    else{
        holder =  (ViewHolder) rowView.getTag();
    }

    Files i = array.get(position);
    if (array.get(position).isFolder() == 1){
        holder.icon.setImageResource(R.drawable.folder);
    }
    else if (array.get(position).isFolder() == 0){
        if (array.get(position).getFileType().contains("image") || array.get(position).getFileType().contains("picture"))
            holder.icon.setImageResource(R.drawable.image);
        else if (array.get(position).getFileType().contains("sound")|| array.get(position).getFileType().contains("music"))
            holder.icon.setImageResource(R.drawable.audio);
        else if (array.get(position).getFileType().contains("video")|| array.get(position).getFileType().contains("film"))
            holder.icon.setImageResource(R.drawable.video);
        else
            holder.icon.setImageResource(R.drawable.file);
    }
    else
        holder.icon.setImageResource(R.drawable.back);

    holder.fileName.setText(array.get(position).getFileName());
    holder.size.setText(array.get(position).getFileName());

    return rowView;
}

public static class ViewHolder{
    ImageView icon;
    TextView fileName;
    TextView size;
}

}

这是我的MainActivity 

public class MainActivity extends Activity implements View.OnClickListener {

private DropboxAPI<AndroidAuthSession> dropbox;
final static private String ROOT = "/";
private final static String APP_NAME = "dropbox_prefs";
final static private String APP_KEY = "x7bv6zets19iqt4";
final static private String APP_SECRET = "i95y5a09v0wlopu";
private static final int REQUEST_PATH = 1;
private ArrayAdapter<Files> controller = null;

private AlertDialog.Builder alter;
private AlertDialog.Builder inputbuilder;

private String deviceFilePath;
private String deviceFilename;

public ArrayList<Files> listOfFiles = new ArrayList<Files>();
public ArrayList<Files> fileFromDropbox = new ArrayList<Files>();
public ArrayList<String> listOfFolder = new ArrayList<String>();

private Files selected;
private String currentPath = ROOT;
private String previousPath = "";

public boolean isLoggedIn;
public Button logInBut;
public Button uploadBut;
public Button listFilesBut;
ViewStub listView;
private ListView list;




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

    isLoggedIn = false;

    // Creating button on the screen
    logInBut = (Button) findViewById(R.id.logInBut);
    logInBut.setOnClickListener(this);

    uploadBut = (Button) findViewById(R.id.uploadBut);
    uploadBut.setOnClickListener(this);


    listView = (ViewStub) findViewById(R.id.list_stub);
    listView.inflate();
    list = (ListView) findViewById(R.id.list_stub);


    // Create an array to store item >> Init 1 item to make array not null
    fileFromDropbox.add(new Files("1st", "test", 0));
    listOfFiles.add(new Files ("1st", "test", 0));

    controller = new ListFileController(MainActivity.this, android.R.layout.simple_list_item_1,
            listOfFiles);
    list.setAdapter(controller);

    list.setOnItemLongClickListener(new OnItemLongClickListener() {

        @Override
        public boolean onItemLongClick(AdapterView<?> parent, View view,
                                       int position, long id) {
            // TODO Auto-generated method stub
            selected = controller.getItem(position);
            if (selected.isFolder() == 1) {
                folderOptionDialog();
            }
            return true;
        }

    });

    list.setOnItemClickListener(new OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                                int position, long id) {
            // TODO Auto-generated method stub
            selected = controller.getItem(position);
            if (selected.isFolder() == 1) {
                currentPath = selected.getPath();
                updateList(selected.getPath());

            } else if (selected.isFolder() == 2) {
                updateList(selected.getParentPath());

            } else {
                currentPath = selected.getParentPath();
                fileOptions();

            }
            controller.notifyDataSetChanged();
        }
    });
    // Authentication dropbox API account
    checkLogIn(false);
    AppKeyPair appKeys = new AppKeyPair(APP_KEY, APP_SECRET);
    AndroidAuthSession session = new AndroidAuthSession(appKeys);
    dropbox = new DropboxAPI<AndroidAuthSession>(session);
    dropbox.getSession().startOAuth2Authentication(MainActivity.this);


    ConnectivityManager connectivityChecker = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);

    //For 3G check
    boolean is3G = connectivityChecker.getNetworkInfo(ConnectivityManager.TYPE_MOBILE)
            .isConnectedOrConnecting();
    //For WiFi Check
    boolean isWifi = connectivityChecker.getNetworkInfo(ConnectivityManager.TYPE_WIFI)
            .isConnectedOrConnecting();

    if (!is3G && !isWifi)
        Toast.makeText(MainActivity.this, "Please connect to the internet", Toast.LENGTH_LONG).show();
    if (!isWifi)
        Toast.makeText(MainActivity.this, "3G service is currently not available, please connect via WIFI", Toast.LENGTH_LONG).show();


}


private void setAdapter() {

        controller = new ListFileController(this,android.R.layout.simple_list_item_1, listOfFiles);
        list.setAdapter(controller);
        list.setOnItemClickListener(new OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {
                // TODO Auto-generated method stub
                selected = controller.getItem(position);

                if (selected.isFolder() == 1) {
                    currentPath = selected.getPath();
                    updateList(selected.getPath());

                } else if (selected.isFolder() == 2) {
                    updateList(selected.getParentPath());

                } else {
                    currentPath = selected.getParentPath();
                    fileOptions();

                }
                controller.notifyDataSetChanged();
            }
        });

        list.setOnItemLongClickListener(new OnItemLongClickListener(){

            @Override
            public boolean onItemLongClick(AdapterView<?> parent, View view,
                                           int position, long id) {
                // TODO Auto-generated method stub
                selected = controller.getItem(position);
                if (selected.isFolder() == 1) {
                    folderOptionDialog();
                }
                return true;
            }

        });
}

这是我的XML文件，其中包含列表。

<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >

<LinearLayout
android:id="@+id/LinearLayout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<Button
    android:id="@+id/logInBut"
    android:layout_marginLeft = "15dp"
    android:layout_marginRight="15dp"
    android:layout_width="373dp"
    android:layout_height="243dp"
    android:textColor="#43b8e3"
    android:text="LOG IN"
    android:textSize="100dp"
    android:layout_gravity="center_horizontal"
    android:enabled="false" />

<Button
    android:id="@+id/uploadBut"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="UPLOAD"
    android:textColor="#43b8e3"
    android:textSize="80dp"
    android:layout_weight="0.01"
    android:layout_gravity="center_horizontal" />


<ViewStub
    android:id="@+id/list_stub"
    android:inflatedId="@+id/showlayout"
    android:layout="@layout/activity_list_file"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_marginTop="10dp"/>


</LinearLayout>
</merge>

最后一个是布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">

<ListView android:id="@android:id/list"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />
</LinearLayout>

1 个答案:

答案 0 :(得分：3)

这是您的ListView XML：

<ListView android:id="@android:id/list"
   android:layout_width="match_parent"
   android:layout_height="wrap_content" />
</LinearLayout>

这是你的Java，创建一个对它的引用：

list = (ListView) findViewById(R.id.list_stub);

您使用的是错误的资源标识符。将行更改为：

list = (ListView) findViewById(android.R.id.list);
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