如何从Java类中调用片段方法？

Question

我尝试从Java类调用片段方法：我知道关于该主题的堆栈溢出问题很多，但我的情况有所不同

ConnectionAsyncTask.java：

import android.app.Activity;
import android.os.AsyncTask;

import java.util.List;

public class ConnectionAsyncTask extends AsyncTask<String,String,String> {
    Activity activity;
    private EventListener listener;

    public ConnectionAsyncTask(Activity activity) {
        this.activity=activity;
    }
    @Override
    protected String doInBackground(String... params) {
        String content =HttpManager.getData(params[0]);
        return content;
    }
    @Override
    protected void onProgressUpdate(String... values) {
        super.onProgressUpdate(values);
    }
    @Override
    protected void onPostExecute(String s) {
        List<Country> countries= CountryJasonParser.getObjectFromJason(s);
        if (countries != null) {
            String s1 = "";

                s1=s1+"\n"+"" + countries.get(0).getDes() ;
        //i want to call DisplyOnTextView(s1) 
        } 
    }
}

countryfragment.java：

    import android.content.Intent;
    import android.os.Bundle;
    import android.support.design.widget.NavigationView;
    import android.view.LayoutInflater;
    import android.view.MenuItem;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ImageButton;
    import android.widget.ImageView;
    import android.widget.TextView;

    public class countryfragment extends android.support.v4.app.Fragment implements NavigationView.OnNavigationItemSelectedListener {
        TextView desc;

        public countryfragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

            ConnectionAsyncTask connectionAsyncTask = new ConnectionAsyncTask(getActivity());
//This is a server which contains data to load it            connectionAsyncTask.execute("http://www.mocky.io/v2/570d3677270000f600dc29b6");
            View view = inflater.inflate(R.layout.fragment_countryfragment,container,false);
            desc = (TextView) view.findViewById(R.id.desc);

            return view;
        }
        public void DisplyOnTextView(String s) {
            desc.setText(s);
        }

        @Override
        public boolean onNavigationItemSelected(MenuItem item) {
            return false;
        }
    }

---

结果必须是：在文本视图上显示数据。

Answer 1

您不能从AsyncTask直接更新UI视图。 出于您的目的，您可以有一个侦听器，以便它在countryfragment.java触发函数回调，并且可以从回调函数中使用结果更新TextView 。

我猜您首先已经有了这样的界面。

public interface EventListener {
    public void responseReceiver(String result);
}

现在，在您的Fragment实现EventListener并Override responseReceiver方法。

public class countryfragment extends 
    android.support.v4.app.Fragment implements 
    NavigationView.OnNavigationItemSelectedListener
    , EventListener {

    // Other code goes here 

    // Override the callback function
    @Override
    public void responseReceiver(String result) {
        DisplyOnTextView(result);
    }
}

现在，当启动AsyncTask您需要像这样传递正确的侦听器：

ConnectionAsyncTask connectionAsyncTask = new ConnectionAsyncTask(getActivity());
connectionAsyncTask.listener = this;
connectionAsyncTask.execute();

现在像这样更改您的onPostExecute ：

@Override
protected void onPostExecute(String s) {
    List<Country> countries= CountryJasonParser.getObjectFromJason(s);
    if (countries != null) {
        String s1 = "";

         s1=s1+"\n"+"" + countries.get(0).getDes() ;
         listener.responseReceiver(s1);
    }
}

Answer 2

尝试这个：

public class ConnectionAsyncTask extends AsyncTask<String,String,String> {
    Activity activity;
    private EventListener listener;
    private TextView mTextView

    public ConnectionAsyncTask(Activity activity, TextView txt) {
        this.activity=activity;
       this.mTextView=txt;
    }
    @Override
    protected String doInBackground(String... params) {
        String content =HttpManager.getData(params[0]);
        return content;
    }
    @Override
    protected void onProgressUpdate(String... values) {
        super.onProgressUpdate(values);
    }
    @Override
    protected void onPostExecute(String s) {
        List<Country> countries= CountryJasonParser.getObjectFromJason(s);
        if (countries != null) {
            String s1 = "";

                s1=s1+"\n"+"" + countries.get(0).getDes() ;

                mTextView.setText(s1);
        } 
    }
}

接着

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {


        View view = inflater.inflate(R.layout.fragment_countryfragment,container,false);
        desc = (TextView) view.findViewById(R.id.desc);
        ConnectionAsyncTask connectionAsyncTask = new ConnectionAsyncTask(getActivity(), desc);
        connectionAsyncTask.execute("http://www.mocky.io/v2/570d3677270000f600dc29b6");

        return view;
    }

Answer 3

您只需要将活动中的侦听器发送到asyncTask即可从onPostExecute进行调用

码：

    public class Task extends AsyncTask<String,String,String> {

    private TaskListener _listenr;
    public Task(TaskListener listener) {
        _listenr = listener;
    }
    @Override
    protected String doInBackground(String... params) {
       String res = "";

       //some logic

       return res;
    }
    @Override
    protected void onProgressUpdate(String... values) {
        super.onProgressUpdate(values);
    }
    @Override
    protected void onPostExecute(String s) {
        //some logic
        if(_listenr!=null)
        {
            _listenr.onRetrieveData(s);
        }
    }

    public interface TaskListener
    {
        public void onRetrieveData(String res);
    }
}

Fragment:

    public class countryfragment extends Activity implements TaskListener {
    TextView desc;

    public countryfragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        ConnectionAsyncTask connectionAsyncTask = new ConnectionAsyncTask(this);
//This is a server which contains data to load it            connectionAsyncTask.execute("http://www.mocky.io/v2/570d3677270000f600dc29b6");
        View view = inflater.inflate(R.layout.fragment_countryfragment,container,false);
        desc = (TextView) view.findViewById(R.id.desc);

        return view;
    }
    public void DisplyOnTextView(String s) {
        desc.setText(s);
    }

    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        return false;
    }

    @Override
    public void onRetrieveData(String res)
    {
        //some logic here with res

    }
}

Answer 4

尽管不建议对HTTP调用使用AsyncTask，但您可能仍想在ConnectionAsyncTask中创建一个接口，例如

interface ConnectionAsyncTaskCallback{

    void performAction(String s);
}

然后在您的片段中实现此接口

    public class countryfragment extends android.support.v4.app.Fragment implements NavigationView.OnNavigationItemSelectedListener, ConnectionAsyncTask.ConnectionAsyncTaskCallback

您将必须实现performAction(String s)方法，该方法将包含desc.setText(s);

最后，在ConnectionAsyncTask添加成员ConnectionAsyncTaskCallback callback; 您将在构造函数中执行此操作，最后在onPostExecute （ callback.performAction(s1); ）上callback.performAction(s1); 。

TL; DR，这是修改后的代码：

ConnectionAsyncTask：

    public class ConnectionAsyncTask extends AsyncTask<String,String,String> {
    Activity activity;
    private EventListener listener;
    private ConnectionAsyncTaskCallback callback;

    public ConnectionAsyncTask(Activity activity, ConnectionAsyncTaskCallback callback) {
        this.activity=activity;
        this.callback = callback;
    }
    @Override
    protected String doInBackground(String... params) {
        String content =HttpManager.getData(params[0]);
        return content;
    }
    @Override
    protected void onProgressUpdate(String... values) {
        super.onProgressUpdate(values);
    }
    @Override
    protected void onPostExecute(String s) {
        List<Country> countries= CountryJasonParser.getObjectFromJason(s);
        if (countries != null) {
            String s1 = "";

                s1=s1+"\n"+"" + countries.get(0).getDes() ;
        //i want to call DisplyOnTextView(s1) 
            callback.performAction(s1);
        } 

    }

    interface ConnectionAsyncTaskCallback {

        void performAction(String s);
    }
}

乡村片段类别：

public class countryfragment extends android.support.v4.app.Fragment implements NavigationView.OnNavigationItemSelectedListener, ConnectionAsyncTask.ConnectionAsyncTaskCallback {
        TextView desc;

        public countryfragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

            ConnectionAsyncTask connectionAsyncTask = new ConnectionAsyncTask(getActivity());
//This is a server which contains data to load it            connectionAsyncTask.execute("http://www.mocky.io/v2/570d3677270000f600dc29b6");
            View view = inflater.inflate(R.layout.fragment_countryfragment,container,false);
            desc = (TextView) view.findViewById(R.id.desc);

            return view;
        }

        @Override
        public void performAction(String s) {
            desc.setText(s);
        }

        @Override
        public boolean onNavigationItemSelected(MenuItem item) {
            return false;
        }
}