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Ich weiß, was ist ein Null Pointer Ausnahme, aber meine Frage ist, ich bin nicht in der Lage, herauszufinden, wie man damit umgehen und eine Toast-Nachricht an den Benutzer sagen die Liste ist null im folgenden Code. Ich erstelle eine Bildergalerie für meine App und gebe den Pfad an, aus dem das System alle Dateien und Ordner in meine Android-Anwendung laden soll.Nicht in der Lage, herauszufinden, wo die Länge Array überprüfen
Wenn es keine Dateien oder Ordner in dem Pfad, sagen die App stürzt ab:
Attempting to invoke length on a null array.
GalleryFragment.java
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_gallery, container, false);
toolbar = (Toolbar) getActivity().findViewById(R.id.toolbar);
ImageView icon = (ImageView) getActivity().findViewById(R.id.toolbarIcon);
icon.setImageResource(R.drawable.ic_perm_media_black_24dp);
icon.setColorFilter(getResources().getColor(R.color.Gallery));
TextView title = (TextView) getActivity().findViewById(R.id.toolbarTitle);
title.setText(getString(R.string.galleryLabel));
toolbar.setBackground(getResources().getDrawable(R.drawable.tile_green));
toolbar.setNavigationIcon(getResources().getDrawable(R.drawable.ic_menu_green_24dp));
gridView = (GridView) view.findViewById(R.id.gridView);
setGridAdapter(Environment.getExternalStorageDirectory().getPath());
return view;
}
private void setGridAdapter(String path) {
// Create a new grid adapter
gridItems = createGridItems(path);
MyGridAdapter adapter = new MyGridAdapter(getContext(), gridItems);
// Set the grid adapter
gridView.setAdapter(adapter);
// Set the onClickListener
gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
if (gridItems.get(position).isDirectory()) {
setGridAdapter(gridItems.get(position).getPath());
}
else {
gridItems.get(position).getImage();
}
}
});
gridView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
@Override
public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
if (gridItems.get(position).isDirectory()) {
Dialog dialog = new Dialog(getContext());
dialog.setTitle("Test");
dialog.setContentView(R.layout.activity_recognition);
dialog.show();
return false;
} else {
Dialog dialog = new Dialog(getContext());
dialog.setTitle("Test");
dialog.setContentView(R.layout.activity_reset_password);
dialog.show();
return false;
}
}
});
}
private List<GridViewItem> createGridItems(String directoryPath) {
List<GridViewItem> items = new ArrayList<>();
// List all the items within the folder.
File[] files = new File(directoryPath).listFiles(new ImageFileFilter());
for (File file : files) {
// Add the directories containing images or sub-directories
if (file.isDirectory()
&& file.listFiles(new ImageFileFilter()).length > 0) {
items.add(new GridViewItem(file.getAbsolutePath(), true, null));
}
// Add the images
else {
Bitmap image = BitmapHelper.decodeBitmapFromFile(file.getAbsolutePath(),
50,
50);
items.add(new GridViewItem(file.getAbsolutePath(), false, image));
}
}
return items;
}
/**
* Checks the file to see if it has a compatible extension.
*/
private boolean isImageFile(String filePath) {
if (filePath.endsWith(".jpg") || filePath.endsWith(".png"))
// Add other formats as desired
{
return true;
}
return false;
}
/**
* This can be used to filter files.
*/
private class ImageFileFilter implements FileFilter {
@Override
public boolean accept(File file) {
if (file.isDirectory()) {
return true;
}
else if (isImageFile(file.getAbsolutePath())) {
return true;
}
return false;
}
}
GalleryAdapter.java
public class MyGridAdapter extends BaseAdapter {
LayoutInflater inflater;
List <GridViewItem> items;
private Context mContext;
public MyGridAdapter(Context context, List <GridViewItem> items) {
mContext = context;
this.items = items;
inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
@Override
public int getCount() {
return items.size();
}
@Override
public Object getItem(int position) {
return items.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = inflater.inflate(R.layout.grid_item, null);
}
TextView text = (TextView) convertView.findViewById(R.id.textView);
text.setText(items.get(position).getPath());
ImageView imageView = (ImageView) convertView.findViewById(R.id.imageView);
Bitmap image = items.get(position).getImage();
if (image != null) {
imageView.setImageBitmap(image);
} else {
// If no image is provided, display a folder icon.
imageView.setImageResource(R.drawable.ic_folder_grey_24dp);
}
return convertView;
}
}
Ich möchte Dateien nur dann auflisten, wenn die Länge des Arrays größer als Null ist. Ich weiß nicht, wo ich nachsehen soll.