Question

我想在我的应用的侧边菜单中添加货币转换器。但是我在点击（）之后无法获得转换。点击＆＃34;计算＆＃34;我没有得到转换。请参阅代码为什么我无法点击。我用过雅虎api。

CurrencyConverter.java

import android.app.Fragment;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

import info.androidhive.customlistviewvolley.R;


public class CurrencyConverter extends Fragment {
    public CurrencyConverter() {
    }
    TextView t;
    public int to;
    public int from;
    public String[] val;
    public String s;
    public Handler handler;


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


         View rootView = inflater.inflate(R.layout.currency_converter, container, false);
        t= (TextView) rootView.findViewById(R.id.textView4);
        Spinner s1 = (Spinner) rootView.findViewById(R.id.spinner1);
        Spinner s2 = (Spinner) rootView.findViewById(R.id.spinner2);
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
                this.getActivity(), R.array.name, android.R.layout.simple_spinner_item);
        adapter.setDropDownViewResource(android.R.layout.select_dialog_singlechoice);
        val = getResources().getStringArray(R.array.value);
        s1.setAdapter(adapter);
        s2.setAdapter(adapter);
        s1.setOnItemSelectedListener(new spinOne(1));
        s2.setOnItemSelectedListener(new spinOne(2));

        Button b = (Button) rootView.findViewById(R.id.button1);
        b.setOnClickListener(new View.OnClickListener() {
            public void onClick(View rootView) {


//t.setText(exResult);
                if (from == to) {
                    Toast.makeText(getActivity().getApplicationContext(), "Invalid", 4000).show();
                } else {
                    try {
                        //  s = getJson("http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.xchange%20where%20pair%20in%20(%22"+val[from]+val[to]+"%22)&format=json&diagnostics=true&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys&callback=");
                        JSONObject jObj;
                        jObj = new JSONObject(s);
                        String exResult = jObj.getJSONObject("query").getJSONObject("results").getJSONObject("rate").getString("Rate");
                        t.setText(exResult);
                    } catch (JSONException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            }




        });
        return rootView;
    }

    public class calculate extends AsyncTask<String, String, String> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();

        }

        @Override
        protected String doInBackground(String... args) {

            try {

                s = getJson("http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.xchange%20where%20pair%20in%20(%22"+val[from]+val[to]+"%22)&format=json&diagnostics=true&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys&callback=");
                JSONObject jObj;
                jObj = new JSONObject(s);
                String exResult = jObj.getJSONObject("query").getJSONObject("results").getJSONObject("rate").getString("Rate");
              //  t.setText(exResult);

            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (ClientProtocolException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return s;

        }

        @Override
        protected void onPostExecute(String exResult) {
           //  t = (TextView) rootView.findViewById(R.id.textView4);
         //  t.setText(exResult);
        }

       }

    public String getJson(String url)throws ClientProtocolException, IOException {

        StringBuilder build = new StringBuilder();
        HttpClient client = new DefaultHttpClient();
        HttpGet httpGet = new HttpGet(url);
        HttpResponse response = client.execute(httpGet);
        HttpEntity entity = response.getEntity();
        InputStream content = entity.getContent();
        BufferedReader reader = new BufferedReader(new InputStreamReader(content));
        String con;
        while ((con = reader.readLine()) != null) {
            build.append(con);
        }
        return build.toString();
    }

        public class spinOne implements AdapterView.OnItemSelectedListener
        {
            int ide;
            spinOne(int i)
            {
                ide =i;
            }
            public void onItemSelected(AdapterView<?> parent, View view,
                                       int index, long id) {
                if(ide == 1)
                    from = index;
                else if(ide == 2)
                    to = index;

            }

            public void onNothingSelected(AdapterView<?> arg0) {
                // TODO Auto-generated method stub
            }

    }
}

CurrencyConverter.xml

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="#FFFFFF"
    >
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:background="#FFFFFF">

        <TextView
            android:id="@+id/textView1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/one"
            android:textAppearance="?android:attr/textAppearanceLarge" />

        <Spinner
            android:id="@+id/spinner1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

        <TextView
            android:id="@+id/textView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/in"
            android:textAppearance="?android:attr/textAppearanceLarge" />

        <Spinner
            android:id="@+id/spinner2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

        <TextView
            android:id="@+id/textView3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/equal"
            android:textAppearance="?android:attr/textAppearanceLarge" />




        <RelativeLayout
            android:id="@+id/relativeLayout1"
            android:layout_width="match_parent"
            android:layout_height="122dp"
            android:gravity="center"
            android:background="#ffffff">



            <RelativeLayout
                android:id="@+id/relativeLayout2"
                android:layout_width="match_parent"
                android:layout_height="120dp"
                android:gravity="center"
                android:background="#ffffff">
                <TextView
                    android:id="@+id/textView4"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_alignParentLeft="true"
                    android:layout_alignParentTop="true"
                    android:text="@string/result"
                    android:textSize="35dp"
                    />
            </RelativeLayout>



        </RelativeLayout>

        <Button
            android:id="@+id/button1"
            android:layout_marginTop="10dp"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:text="@string/calculate" />
    </LinearLayout>
</ScrollView>

错误：

05-09 17:33:30.425 2238-2238/? E/AndroidRuntime: FATAL EXCEPTION: main
                                                 Process: info.androidhive.customlistviewvolley, PID: 2238
                                                 java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
                                                     at org.json.JSONTokener.nextCleanInternal(JSONTokener.java:116)
                                                     at org.json.JSONTokener.nextValue(JSONTokener.java:94)
                                                     at org.json.JSONObject.<init>(JSONObject.java:156)
                                                     at org.json.JSONObject.<init>(JSONObject.java:173)
                                                     at info.androidhive.customlistviewvolley.model.CurrencyConverter$1.onClick(CurrencyConverter.java:74)
                                                     at android.view.View.performClick(View.java:4756)
                                                     at android.view.View$PerformClick.run(View.java:19749)
                                                     at android.os.Handler.handleCallback(Handler.java:739)
                                                     at android.os.Handler.dispatchMessage(Handler.java:95)
                                                     at android.os.Looper.loop(Looper.java:135)
                                                     at android.app.ActivityThread.main(ActivityThread.java:5221)
                                                     at java.lang.reflect.Method.invoke(Native Method)
                                                     at java.lang.reflect.Method.invoke(Method.java:372)
                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
05-09 17:33:30.430 1233-1513/? W/ActivityManager:   Force finishing activity info.androidhive.customlistviewvolley/.MainActivity

Answer 1

您正尝试从没有连接的UI线程调用String。作为可能的解决方法之一，您可以创建全局变量并在

分配给它

 @Override
        protected void onPostExecute(String exResult) {
           //  t = (TextView) rootView.findViewById(R.id.textView4);
         //  t.setText(exResult);
             globalString = exResult;
        }

之后您可以使用它代码。请阅读AsyncTask生命周期和Android Threads。

Answer 2

更新答案：

CurreencyConverter.java

import android.app.Fragment;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

import info.androidhive.customlistviewvolley.R;


public class CurrencyConverter extends Fragment {
    public CurrencyConverter() {
    }
    TextView t;
    public int to;
    public int from;
    public String[] val;
    public String s;
    String exResult;
    public Handler handler;


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


         View rootView = inflater.inflate(R.layout.currency_converter, container, false);
        t= (TextView) rootView.findViewById(R.id.textView4);
        Spinner s1 = (Spinner) rootView.findViewById(R.id.spinner1);
        Spinner s2 = (Spinner) rootView.findViewById(R.id.spinner2);
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
                this.getActivity(), R.array.name, android.R.layout.simple_spinner_item);
        adapter.setDropDownViewResource(android.R.layout.select_dialog_singlechoice);
        val = getResources().getStringArray(R.array.value);
        s1.setAdapter(adapter);
        s2.setAdapter(adapter);
        s1.setOnItemSelectedListener(new spinOne(1));
        s2.setOnItemSelectedListener(new spinOne(2));

        Button b = (Button) rootView.findViewById(R.id.button1);
        b.setOnClickListener(new View.OnClickListener() {
            public void onClick(View View) {



                if (from == to) {
                    Toast.makeText(getActivity().getApplicationContext(), "Invalid", 4000).show();
                } else {
                    new calculate().execute();

                }
            }

        });
        return rootView;
    }

    public class calculate extends AsyncTask<String, String, String> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();

        }

        @Override
        protected String doInBackground(String... args) {

            try {

                s = getJson("http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.xchange%20where%20pair%20in%20(%22"+val[from]+val[to]+"%22)&format=json&diagnostics=true&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys&callback=");
                JSONObject jObj;
                jObj = new JSONObject(s);
                 exResult = jObj.getJSONObject("query").getJSONObject("results").getJSONObject("rate").getString("Rate");


            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (ClientProtocolException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return exResult;

        }
        @Override
        protected void onPostExecute(String exResult) {

           t.setText(exResult);
        }



       }

    public String getJson(String url)throws  IOException {

        StringBuilder build = new StringBuilder();
        HttpClient client = new DefaultHttpClient();
        HttpGet httpGet = new HttpGet(url);
        HttpResponse response = client.execute(httpGet);
        HttpEntity entity = response.getEntity();
        InputStream content = entity.getContent();
        BufferedReader reader = new BufferedReader(new InputStreamReader(content));
        String con;
        while ((con = reader.readLine()) != null) {
            build.append(con);
        }
        return build.toString();
    }

        public class spinOne implements AdapterView.OnItemSelectedListener
        {
            int ide;
            spinOne(int i)
            {
                ide =i;
            }
            public void onItemSelected(AdapterView<?> parent, View view,
                                       int index, long id) {
                if(ide == 1)
                    from = index;
                else if(ide == 2)
                    to = index;

            }

            public void onNothingSelected(AdapterView<?> arg0) {
                // TODO Auto-generated method stub
            }

    }
}

OnClick（）不适用于货币转换器。

2 个答案: