从适配器回调

Question

所以我有一个自定义的listview。就像Instagram布局一样，每个列表项中都有1张图片和一堆按钮。所以这是问题所在：

我要实现共享按钮。为此，我尝试创建一个从适配器到活动的回调。但这似乎没有用。这是我到目前为止的内容（我裁剪了不相关的部分）：

主要活动

public class MainActivity extends ActionBarActivity implements ListAdapter.OnShareClickedListener{

    ListView main_list;
    List<String> url_list;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        main_list = (ListView) findViewById(R.id.listView);
        ListAdapter nListAdapter = new ListAdapter(context, url_list);
        main_list.setAdapter(nListAdapter);
    }

    @Override
    public void ShareClicked(String url) {
        Log.e("Test",url);
    }

}

列表适配器

public class ListAdapter extends BaseAdapter implements View.OnClickListener {

    OnShareClickedListener mCallback;
    Context context;
    public static List<String> url_list;

    public ListAdapter(Context c, List<String> list) {
        this.context = c;
        url_list = list;
    }

    public interface OnShareClickedListener {
        public void ShareClicked(String url);
    }


    @Override
    public void onClick(View v) {
                mCallback.ShareClicked("Share this text.");
        }
    }

}

错误日志：

Attempt to invoke interface method 'void com.packagename.ListAdapter$OnShareClickedListener.ShareClicked(java.lang.String)' on a null object reference

Answer 1

您需要告诉适配器使用哪个OnShareClickedListener（）实现。现在，在您的适配器中，从未将字段mCallback分配给它，或者您需要在适配器中具有setOnSharedClickedListener（）方法，然后从mainActivity调用该方法并将其设置为mainActivity的实现，或者需要使用构造函数。

我的建议是使用setter而不是构造函数。因此，您需要做的就是这个。

您的ListAdapter

public class ListAdapter extends BaseAdapter implements View.OnClickListener {

    OnShareClickedListener mCallback;
    Context context;
    public static List<String> url_list;

    public ListAdapter(Context c, List<String> list) {
        this.context = c;
        url_list = list;
    }

    public void setOnShareClickedListener(OnShareClickedListener mCallback) {
        this.mCallback = mCallback;
    }

    public interface OnShareClickedListener {
        public void ShareClicked(String url);
    }


    @Override
    public void onClick(View v) {
        mCallback.ShareClicked("Share this text.");
    }
}

您的MainActivty

public class MainActivity extends ActionBarActivity implements ListAdapter.OnShareClickedListener{

    ListView main_list;
    List<String> url_list;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        main_list = (ListView) findViewById(R.id.listView);
        ListAdapter nListAdapter = new ListAdapter(this, url_list);
        nListAdapter.setOnShareClickedListener(this);
        main_list.setAdapter(nListAdapter);
    }

    @Override
    public void ShareClicked(String url) {
        Log.e("Test", url);
    }

}