Question

我有一个主要的活动，它将执行asynctask，然后使用interface将数据发送回活动，看起来像下面的代码

主要活动

 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_profile_scroll);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);

    String type = "getProfile";

    SharedPreferences pref = getApplicationContext().getSharedPreferences("MyPref", 0); // 0 - for private mode
    SharedPreferences.Editor editor = pref.edit();
    String username = pref.getString("username", null);

    RetrieveData retrieveData = new RetrieveData(this);

    retrieveData.execute(type,username);
}

public void sendData(String response) {
    // TODO Auto-generated method stub
    String name="";
    String age="";
    String gender = "";
    String id = "";
    try {
        JSONObject jsonObject = new JSONObject(response);
        JSONArray result = jsonObject.getJSONArray("result");
        JSONObject collegeData = result.getJSONObject(0);
        ImageView imageView = (ImageView) findViewById(R.id.imageView2);

        name = collegeData.getString("name");
        age = collegeData.getString("age");
        gender = collegeData.getString("gender");
        id = collegeData.getString("id");
        EditText MyName = (EditText) findViewById(R.id.editText14);
        MyName.setText(name);
        EditText MyAge = (EditText) findViewById(R.id.editText21);
        MyAge.setText(age);
        EditText MyGender = (EditText) findViewById(R.id.editText22);
        MyGender.setText(gender);
        Picasso.with(this).load("http://192.168.12.252/"+id+"/profile.png").memoryPolicy(MemoryPolicy.NO_CACHE).networkPolicy(NetworkPolicy.NO_CACHE).into(imageView);
    } catch (JSONException e) {
        e.printStackTrace();
    }
}

的AsyncTask

public class RetrieveData extends AsyncTask<String,Void,String>{
    Context context;
    RetrieveData(Context ctx) {
        context = ctx;
    }
    private OnDataSendToActivity dataSendToActivity;

    public RetrieveData(View.OnClickListener activity){
        dataSendToActivity = (OnDataSendToActivity)activity;
    }

    @Override
    protected String doInBackground(String... params) {
        String profile_url = "http://192.168.12.252/getprofile.php";
        String image_url = "http://192.168.12.252/imagelist.php";
        String type = params[0];

        if(type.equals("getProfile")){
            try {
                String user_name = params[1];
                URL url = new URL(profile_url);
                HttpURLConnection httpURLConnection = null;
                httpURLConnection = (HttpURLConnection)url.openConnection();
                httpURLConnection.setRequestMethod("POST");
                httpURLConnection.setDoOutput(true);
                httpURLConnection.setDoInput(true);

                httpURLConnection.setDoOutput(true);
                httpURLConnection.setDoInput(true);
                OutputStream outputStream = httpURLConnection.getOutputStream();
                BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
                String post_data = URLEncoder.encode("user_name", "UTF-8")+"="+URLEncoder.encode(user_name, "UTF-8");
                bufferedWriter.write(post_data);
                bufferedWriter.flush();
                bufferedWriter.close();
                outputStream.close();

                InputStream inputStream = httpURLConnection.getInputStream();
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"iso-8859-1"));
                String result = null;
                result = bufferedReader.readLine();
                bufferedReader.close();
                inputStream.close();
                httpURLConnection.disconnect();
                return result;
            } catch (IOException e) {
                e.printStackTrace();
            }
        }else if(type.equals("getProfileImages")){
            try {
                String user_name = params[1];
                URL url = new URL(image_url);
                HttpURLConnection httpURLConnection = null;
                httpURLConnection = (HttpURLConnection)url.openConnection();
                httpURLConnection.setRequestMethod("POST");
                httpURLConnection.setDoOutput(true);
                httpURLConnection.setDoInput(true);

                httpURLConnection.setDoOutput(true);
                httpURLConnection.setDoInput(true);
                OutputStream outputStream = httpURLConnection.getOutputStream();
                BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
                String post_data = URLEncoder.encode("Image", "UTF-8")+"="+URLEncoder.encode("Image", "UTF-8")+"&"+URLEncoder.encode("user_name", "UTF-8")+"="+URLEncoder.encode(user_name, "UTF-8");
                bufferedWriter.write(post_data);
                bufferedWriter.flush();
                bufferedWriter.close();
                outputStream.close();

                InputStream inputStream = httpURLConnection.getInputStream();
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"iso-8859-1"));
                String result = null;
                result = bufferedReader.readLine();
                bufferedReader.close();
                inputStream.close();
                httpURLConnection.disconnect();
                return result;
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        dataSendToActivity.sendData(result);
    }

接口

public interface OnDataSendToActivity {
    void sendData(String str);
}

当我执行代码时，它会在此行崩溃

dataSendToActivity.sendData(result);

并且android监视器中的错误就像下面我不明白什么是错的

    --------- beginning of crash
03-24 04:12:42.518 20964-20964/com.example.lenovo.maidfriends E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                Process: com.example.lenovo.maidfriends, PID: 20964
                                                                                java.lang.NullPointerException: Attempt to invoke interface method 'void com.example.lenovo.maidfriends.OnDataSendToActivity.sendData(java.lang.String)' on a null object reference
                                                                                    at com.example.lenovo.maidfriends.RetrieveData.onPostExecute(RetrieveData.java:119)
                                                                                    at com.example.lenovo.maidfriends.RetrieveData.onPostExecute(RetrieveData.java:33)
                                                                                    at android.os.AsyncTask.finish(AsyncTask.java:667)
                                                                                    at android.os.AsyncTask.-wrap1(AsyncTask.java)
                                                                                    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:684)
                                                                                    at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                    at android.os.Looper.loop(Looper.java:154)
                                                                                    at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

我认为它说，它在结果中没有任何价值，但不是，结果中有一些东西。

有谁能让我知道什么是错的？

Answer 1

您没有覆盖主要活动中的RetrieveData功能。您只是创建一个具有相同名称的新功能。

而不是将Asynctask称为：

RetrieveData retrieveData = new RetrieveData(this);

使用以下代码：

RetrieveData retrieveData = new RetrieveData(new RetrieveData(){
public void sendData(String response) {
    // TODO Auto-generated method stub
    String name="";
    String age="";
    String gender = "";
    String id = "";
    try {
        JSONObject jsonObject = new JSONObject(response);
        JSONArray result = jsonObject.getJSONArray("result");
        JSONObject collegeData = result.getJSONObject(0);
        ImageView imageView = (ImageView) findViewById(R.id.imageView2);

        name = collegeData.getString("name");
        age = collegeData.getString("age");
        gender = collegeData.getString("gender");
        id = collegeData.getString("id");
        EditText MyName = (EditText) findViewById(R.id.editText14);
        MyName.setText(name);`enter code here`
        EditText MyAge = (EditText) findViewById(R.id.editText21);
        MyAge.setText(age);
        EditText MyGender = (EditText) findViewById(R.id.editText22);
        MyGender.setText(gender);
        Picasso.with(this).load("http://192.168.12.252/"+id+"/profile.png").memoryPolicy(MemoryPolicy.NO_CACHE).networkPolicy(NetworkPolicy.NO_CACHE).into(imageView);
    } catch (JSONException e) {
        e.printStackTrace();
    }

});

删除主要活动的sendData（）

同样在RetrieveData类中，替换以下代码：

 public RetrieveData(View.OnClickListener activity){
        dataSendToActivity = (OnDataSendToActivity)activity;
    }

使用：

public RetrieveData(OnDataSendToActivity activity){
    dataSendToActivity = activity;
}

如果您遇到任何问题，请告诉我。

Answer 2

从sendData()致电onPostExecute简单的事情：

MainActivity ma=new MainActivity();
ma.sendData(result);

发送到活动的数据接口崩溃

2 个答案: