ListActivity崩溃

Question

I wish to open a list of files in a directory when i clicked on a button. Then tap on a item on the list to open the file in a texteditor. But i the app crashes when i run it. any where i have error on the codes?

public class LogActivity extends ListActivity {

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);


    //click to view log file
    Button openButton = (Button)this.findViewById(R.id.btn_opentext);
    openButton.setOnClickListener(new OnClickListener() {
      @Override
      public void onClick(View v) {
          File file = new File (Environment.getExternalStorageDirectory(), "/TEST");

          File[] listfiles = null;

          if(file.isDirectory())
              listfiles = file.listFiles();

          for(int i=0;i<listfiles.length;i++)
              Log.i("FileName", listfiles[i].getName());

        if (!file.exists())
        {
            Toast.makeText(LogActivity.this, "File does not exist", Toast.LENGTH_SHORT).show();
        }
        else
        {

          setListAdapter(new ArrayAdapter<File>(LogActivity.this,
                    android.R.layout.simple_list_item_1, listfiles));
            //tap on item on list to open file
            Intent intent = new Intent();
            intent.setAction(android.content.Intent.ACTION_VIEW);
            intent.setDataAndType(Uri.fromFile(file), "text/plain");
            startActivity(intent);
        }  

      }
    });

Answer 1

Probably your 'TEST' folder doesn't exist on the sdcard, in which case file.listfiles() returns null. Then when you access listfiles.length() (for the 'for loop') you get a NullPointerException.

Move the code that uses listfiles in the 'else' part. In this way when the directory doesn't exist you will get your Toast message shown, and if it exists it will loop to perform your Logs and create your list view.

You could also use file.mkdirs() so that in any case that directory will exist and it will simply use the Empty View when no file is found. (remember also to add the WRITE_EXTERNAL_STORAGE permission if you wish to write to sd card)