java - 显示从服务器检索到的图像

Question

我正在开发一个 Android 应用程序，用户可以在其中上传照片。现在，我从服务器调用一个方法，该方法将返回用户列表。我想将这个列表与照片一起显示。 服务器中存储的图像是字节数组。所以我将它们转换为字符串，然后转换为位图以进行显示。不幸的是，它不起作用，因为我也在使用适配器做事情。适配器类中检索到的图像为空。我做错了什么？

OtherUsers.java:

public class OtherUsers extends Activity {

    private PersonServiceImpl personService = new PersonServiceImpl();

    private static volatile List<RestPerson> restPersonList = new ArrayList<>();

    public static final String firstName = "firstname";
    public static final String userImage = "userimage";

    static final Long userId = (long)0;
    ListView listView;
    UserAdapter userAdapter;

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

        restPersonList = this.personService.getOtherUsers();
       // Base64 base64Encoder = new Base64();

        ArrayList<HashMap<String, String>> usersArrayHashList = new ArrayList<>();
        for(RestPerson restPerson : restPersonList){
            HashMap<String, String> restDisplay = new HashMap<>();
            restDisplay.put("userId",String.valueOf(restPerson.getUserId()));
            restDisplay.put("firstName",restPerson.getFirstName());

           restDisplay.put("userImage","data:image/png;base64," + Base64.encode(restPerson.getProfilePhoto()));
            usersArrayHashList.add(restDisplay);
        }

        listView = (ListView) findViewById(R.id.usersdisplaylist);

        userAdapter = new UserAdapter(this,usersArrayHashList);

        listView.setAdapter(userAdapter);

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {
                Long userid = restPersonList.get(position).getUserId();
                Log.d("Userid is ", String.valueOf(userid));
            }

        });

UserAdapter 类:

public class UserAdapter extends BaseAdapter {

    private Activity activity;
    private ArrayList<HashMap<String, String>> data;
    private static LayoutInflater inflater = null;

    public UserAdapter(Activity a, ArrayList<HashMap<String, String>> d) {
        activity = a;
        data = d;
        inflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }


    @Override
    public int getCount() {
        return data.size();
    }

    @Override
    public Object getItem(int position) {
        return position;
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View view = convertView;
        if (convertView == null)
            view = inflater.inflate(R.layout.userprofiles, null);

        TextView username = (TextView) view.findViewById(R.id.userName);
        ImageView userImage = (ImageView) view.findViewById(R.id.userImage);
        HashMap<String, String> usersList = new HashMap<>();
        usersList = data.get(position);
       username.setText(usersList.get(OtherUsers.firstName));
        String image = usersList.get(OtherUsers.userImage);
        Log.d("Image is ",image);
        byte[] newImageBytes = image.getBytes();
        Bitmap bitmap = BitmapFactory.decodeByteArray(newImageBytes,0,newImageBytes.length);
        userImage.setImageBitmap(bitmap);
        userImage.setImageBitmap(null);
        return view;
    }
}

如果需要任何其他信息，请告诉我。谢谢。

更新 抱歉，忘记放LogCat

08-24 13:43:16.618  29948-29948/internetlegion.com.gradlecheck E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: internetlegion.com.gradlecheck, PID: 29948
    java.lang.NullPointerException: println needs a message
            at android.util.Log.println_native(Native Method)
            at android.util.Log.d(Log.java:139)
            at internetlegion.com.gradlecheck.Adapters.UserAdapter.getView(UserAdapter.java:62)
            at android.widget.AbsListView.obtainView(AbsListView.java:2347)
            at android.widget.ListView.measureHeightOfChildren(ListView.java:1270)
            at android.widget.ListView.onMeasure(ListView.java:1182)
            at android.view.View.measure(View.java:17547)

Answer 1

您在适配器中使用的数据结构非常奇怪。最好创建一个具有三个属性的类，并将这些属性的一个列表发送到适配器类。 无论如何，你的问题是:

public static final String userImage = "userimage";

您使用值userimage定义userImage，然后将“userImage”插入到 HashMap 中，该“userImage”与userImage的值不相等(值i) 是小写的，那么你必须尝试从不存在的 hashmap 中获取“userimage”，因此值为 null。

答案:

您可以更改以下行:

restDisplay.put("userImage","data:image/png;base64," + Base64.encode(restPerson.getProfilePhoto()));

到

restDisplay.put(userImage,"data:image/png;base64," + Base64.encode(restPerson.getProfilePhoto()));

但更好的方法是创建自定义对象。