我正在尝试在单位转换器上制作应用程序。我已经完成了所有其他实现，但我无法获取货币的实时值。我找到了一种“JSON解析”的方法。我搜索它并创建了这个代码。
package com.example.unitconverter;
import java.io.IOException;
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.apache.http.util.EntityUtils;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
public class HttpExample extends Activity{
Spinner S1,S2;
TextView tv;
EditText et;
Button abutton;
HttpClient client;
JSONObject json;
static final String URL = "http://rate-exchange.appspot.com/currency?from=";
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.currency);
S1=(Spinner)findViewById(R.id.spinner1);
S2=(Spinner)findViewById(R.id.spinner2);
et=(EditText)findViewById(R.id.editText1);
tv = (TextView) findViewById (R.id.textView1);
abutton=(Button)findViewById(R.id.button1);
client = new DefaultHttpClient();
abutton.setOnClickListener(new View.OnClickListener() {
public void onClick(View arg0) {
// TODO Auto-generated method stub
new Read().execute("rate");
}
});
}
public JSONObject retrieve(String from,String to) throws ClientProtocolException,IOException,JSONException{
StringBuilder url = new StringBuilder(URL);
url.append(from + "&to=" + to);
HttpGet get = new HttpGet(url.toString());
HttpResponse r = client.execute(get);
int status = r.getStatusLine().getStatusCode();
if(status == 200){
HttpEntity e = r.getEntity();
String data = EntityUtils.toString(e);
JSONArray timeline = new JSONArray(data);
JSONObject last = timeline.getJSONObject(0);
return last;
}
else{
Toast.makeText(HttpExample.this, "error",Toast.LENGTH_SHORT).show();
return null;
}
}
public class Read extends AsyncTask<String,Integer,String>{
@Override
protected void onPreExecute() {
Log.i("AsyncTask", "onPreExecute");
}
@Override
protected String doInBackground(String... params) {
// TODO Auto-generated method stub
try {
json = retrieve(S1.getSelectedItem().toString(),S2.getSelectedItem().toString());
return json.getString(params[0]);
}
catch (Exception e) {
// TODO Auto-generated catch block
Toast.makeText(HttpExample.this, "Exception", Toast.LENGTH_LONG).show();
e.printStackTrace();
return null;
}
}
@Override
protected void onPostExecute(String result) {
// TODO Auto-generated method stub
Double F=Double.parseDouble(result);
Double D = Double.parseDouble(et.getText().toString());
String newstring = Double.toString(D*F);
tv.setText(newstring);
}
}
}
xml 文件包含 2 个包含货币缩写的微调器、1 个 EditText、1 个 TextView 和 1 个按钮“Convert”。当我单击“转换”时，我收到一条消息“不幸的是，UnitConverter 停止工作”。
我是 android 新手，因此对错误了解不多，但我可以从 LogCat 中了解到 doInBackground() 函数存在一些问题。
请帮助，因为我提交此应用程序的最后日期非常接近。
提前致谢。
更新：
04-12 16:26:36.494: E/AndroidRuntime(1853): FATAL EXCEPTION: main
04-12 16:26:36.494: E/AndroidRuntime(1853): java.lang.NullPointerException
04-12 16:26:36.494: E/AndroidRuntime(1853): at java.lang.StringToReal.parseDouble(StringToReal.java:244)
04-12 16:26:36.494: E/AndroidRuntime(1853): at java.lang.Double.parseDouble(Double.java:295)
04-12 16:26:36.494: E/AndroidRuntime(1853): at com.example.unitconverter.HttpExample$Read.onPostExecute(HttpExample.java:119)
04-12 16:26:36.494: E/AndroidRuntime(1853): at com.example.unitconverter.HttpExample$Read.onPostExecute(HttpExample.java:1)
04-12 16:26:36.494: E/AndroidRuntime(1853): at android.os.AsyncTask.finish(AsyncTask.java:631)
04-12 16:26:36.494: E/AndroidRuntime(1853): at android.os.AsyncTask.access$600(AsyncTask.java:177)
04-12 16:26:36.494: E/AndroidRuntime(1853): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
04-12 16:26:36.494: E/AndroidRuntime(1853): at android.os.Handler.dispatchMessage(Handler.java:99)
04-12 16:26:36.494: E/AndroidRuntime(1853): at android.os.Looper.loop(Looper.java:137)
04-12 16:26:36.494: E/AndroidRuntime(1853): at android.app.ActivityThread.main(ActivityThread.java:5041)
04-12 16:26:36.494: E/AndroidRuntime(1853): at java.lang.reflect.Method.invokeNative(Native Method)
04-12 16:26:36.494: E/AndroidRuntime(1853): at java.lang.reflect.Method.invoke(Method.java:511)
04-12 16:26:36.494: E/AndroidRuntime(1853): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
04-12 16:26:36.494: E/AndroidRuntime(1853): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
04-12 16:26:36.494: E/AndroidRuntime(1853): at dalvik.system.NativeStart.main(Native Method)
更新：
我得到了我的错误..我使用的是 JSONArray 而不是 JSONObject。
public JSONObject retrieve(String from,String to) throws ClientProtocolException,IOException,JSONException{
StringBuilder url = new StringBuilder(URL);
url.append(from + "&to=" + to);
HttpGet get = new HttpGet(url.toString());
HttpResponse r = client.execute(get);
int status = r.getStatusLine().getStatusCode();
if(status == 200){
HttpEntity e = r.getEntity();
String data = EntityUtils.toString(e);
JSONObject last = new JSONObject(data);
return last;
}
else{
Toast.makeText(Currency.this, "Error!!!",Toast.LENGTH_SHORT).show();
return null;
}
谢谢大家