Question

In my app I have a header with icon hidden, I have a adapter with a listview when I click the listview I go to a login screen using listener, when the login is successful is should come back to listview(adapter) and icon should get visible on header.

In the login activity I have the following code:

public void onClick(View v) {
    String password = etPassword.getText().toString();
    if(password.equals("guest")){
        SearchAdapter.setImgVisibility();
    } else {
        //-----
    }
    finish();
}

In my adapter I am calling the setImgVisibility() as follows, but it is not working

public static void setImgVisibility() {
    img.setVisibility(View.VISIBLE);
}

I am getting a Nullpointerexception near the line img.setVisibility(View.VISIBLE);
I am stuck here and don’t know what I am doing wrong. Any suggestions or help is appreciated

Answer 1

I would imagine that img is null. You need to look at where this value is set and make sure happens before you call the method setImgVisibility.

Show more of your complete code for people to help further.

Additionally, i’ve just noticed you’ve used a static reference to your search adapter, you should be really careful using statics, especially where any referencing of images is concerned as images can be bound to the context, as such unless you nullify the static you will end up with a memory leak. (this used to be an old problem, not sure its still valid, but i would still avoid using a static reference).

Without more code we’re not likely to be able to properly help you. For example are you switching activities when logging in? If you are, this won’t work at all.

[given the comment below] If you switch activities then your activity containing the list view is going to be destroyed and then rebuilt then you navigate back to it. or it will at least go through the activity lifecycle. This means you can set the icon during the instantiation of the header img.

You could store your logged in state as a property of the Application or a preference. Grab this value when you set the header image and set the image accordingly.