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我正在编写这个用于货币转换的 android 代码，我得到 NullPointerException ：

这是代码，我的 logCat 说错误在第 73 行

public class Currency_convert extends Activity
{
    public int to;
    public int from;
    public String [] val;
    public String s;
    public Handler handler;
    public double am=0.0;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Spinner s1 = (Spinner) findViewById(R.id.spinner11);
        Spinner s2 = (Spinner) findViewById(R.id.spinner22);
        final EditText e=(EditText) findViewById(R.id.amountt);
       // am=Double.parseDouble(e.getText().toString());
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
                this, 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) findViewById(R.id.button11);
        b.setOnClickListener(new OnClickListener(){
            public void onClick(View v) {
                TextView t = (TextView) findViewById(R.id.textView44);  
                if(from == to)
                {
                    Toast.makeText(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=");                       
                    //s=getJson("http://www.google.com/ig/calculator?hl=en&q=1USD=?INR");
                          JSONObject jObj;
                        jObj = new JSONObject(s);
                        String exResult = jObj.getJSONObject("query").getJSONObject("results").getJSONObject("rate").getString("Rate");
                          am=Double.parseDouble(e.getText().toString());
                        double totalR=(Double.parseDouble(exResult))*am;
                        String r=String.valueOf(totalR);
                        t.setText(r);
                        } 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();
                        }                                                    
                    }                                           
                }                               
        });
    }
    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();
    }
    private class spinOne implements 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  
        }

    }
}

错误是此行的运行时错误：

    s2.setAdapter(adapter);

不知道怎么回事！！

这是日志猫：

11-07 10:25:22.194: E/AndroidRuntime(2004): FATAL EXCEPTION: main
11-07 10:25:22.194: E/AndroidRuntime(2004): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.dashboard_our/com.example.dashboard_our.Currency_convert}: java.lang.NullPointerException
11-07 10:25:22.194: E/AndroidRuntime(2004):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
11-07 10:25:22.194: E/AndroidRuntime(2004):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
11-07 10:25:22.194: E/AndroidRuntime(2004):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
11-07 10:25:22.194: E/AndroidRuntime(2004):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
11-07 10:25:22.194: E/AndroidRuntime(2004):     at android.os.Handler.dispatchMessage(Handler.java:99)
11-07 10:25:22.194: E/AndroidRuntime(2004):     at android.os.Looper.loop(Looper.java:137)
11-07 10:25:22.194: E/AndroidRuntime(2004):     at android.app.ActivityThread.main(ActivityThread.java:5103)
11-07 10:25:22.194: E/AndroidRuntime(2004):     at java.lang.reflect.Method.invokeNative(Native Method)
11-07 10:25:22.194: E/AndroidRuntime(2004):     at java.lang.reflect.Method.invoke(Method.java:525)
11-07 10:25:22.194: E/AndroidRuntime(2004):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
11-07 10:25:22.194: E/AndroidRuntime(2004):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-07 10:25:22.194: E/AndroidRuntime(2004):     at dalvik.system.NativeStart.main(Native Method)
11-07 10:25:22.194: E/AndroidRuntime(2004): Caused by: java.lang.NullPointerException
11-07 10:25:22.194: E/AndroidRuntime(2004):     at com.example.dashboard_our.Currency_convert.onCreate(Currency_convert.java:73)
11-07 10:25:22.194: E/AndroidRuntime(2004):     at android.app.Activity.performCreate(Activity.java:5133)
11-07 10:25:22.194: E/AndroidRuntime(2004):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
4

2 回答 2

1

好像findViewById(R.id.spinner22)回来了null。当您在 XML 布局中没有 ID 为 spinner22 的对象时，就会发生这种情况。

于 2013-11-07T15:38:58.907 回答
1

这条线失败了：

        Spinner s2 = (Spinner) findViewById(R.id.spinner22);

没有 logcat 很难看到，但您可以查看以下内容来诊断/修复它：

  1. spinner22 不是您布局中的有效 id
  2. 具有该 id 的项目不是 Spinner
  3. 你清理过你的项目吗？
  4. 通过调试器运行它，在失败的行上设置一个断点，看看发生了什么。
于 2013-11-07T15:41:30.317 回答