我想从服务器调用json数组
此行适用于我
JSONObject json = JSONfunctions.getJSONfromURL("http://midsweden.gofreeserve.com/fetch.php");
但是当我尝试使用我的sharedprefences类获取时它不起作用并且强制要停止，这里是代码
JSONObject json = JSONfunctions.getJSONfromURL("http://midsweden.gofreeserve.com/fetch.php?identifier="
+ Test.this.myprefs.getEmail());
在eclipse中，它没有指出任何错误，我的意思是缺少var减速但它不起作用。任何建议???
以下是我在logcat中看到的内容
05-02 19:49:53.569: ERROR/AndroidRuntime(20721): Uncaught handler: thread main exiting due to uncaught exception
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.droidnova.android.howto.optionmenu/com.droidnova.android.howto.optionmenu.Test}: java.lang.NullPointerException
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2596)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2621)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at android.app.ActivityThread.access$2200(ActivityThread.java:126)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1932)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at android.os.Handler.dispatchMessage(Handler.java:99)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at android.os.Looper.loop(Looper.java:123)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at android.app.ActivityThread.main(ActivityThread.java:4595)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at java.lang.reflect.Method.invokeNative(Native Method)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at java.lang.reflect.Method.invoke(Method.java:521)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at dalvik.system.NativeStart.main(Native Method)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): Caused by: java.lang.NullPointerException
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at com.droidnova.android.howto.optionmenu.Test.onCreate(Test.java:37)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2544)
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): ... 11 more
05-02 19:49:53.778: ERROR/ActivityManager(97): fail to set top app changed!
05-02 19:49:58.048: ERROR/PackageInstallationReceiver(248): Remove /data/local/tmp/com.droidnova.android.howto.optionmenu.apk Fail!
05-02 19:51:41.418: ERROR/AndroidRuntime(20746): ERROR: thread attach failed
05-02 19:51:42.818: ERROR/AndroidRuntime(20754): ERROR: thread attach failed
05-02 19:51:43.438: ERROR/AndroidRuntime(20762): Uncaught handler: thread main exiting due to uncaught exception
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.droidnova.android.howto.optionmenu/com.droidnova.android.howto.optionmenu.Test}: java.lang.NullPointerException
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2596)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2621)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at android.app.ActivityThread.access$2200(ActivityThread.java:126)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1932)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at android.os.Handler.dispatchMessage(Handler.java:99)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at android.os.Looper.loop(Looper.java:123)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at android.app.ActivityThread.main(ActivityThread.java:4595)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at java.lang.reflect.Method.invokeNative(Native Method)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at java.lang.reflect.Method.invoke(Method.java:521)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at dalvik.system.NativeStart.main(Native Method)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): Caused by: java.lang.NullPointerException
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at com.droidnova.android.howto.optionmenu.Test.onCreate(Test.java:37)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2544)
05-02 19:51:43.448: ERROR/AndroidRuntime(20762): ... 11 more
05-02 19:51:45.178: ERROR/ActivityManager(97): fail to set top app changed!
05-02 19:51:54.428: ERROR/AndroidRuntime(20772): ERROR: thread attach failed
05-02 19:51:55.818: ERROR/AndroidRuntime(20780): ERROR: thread attach failed
05-02 19:51:56.528: ERROR/AndroidRuntime(20788): Uncaught handler: thread main exiting due to uncaught exception
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.droidnova.android.howto.optionmenu/com.droidnova.android.howto.optionmenu.Test}: java.lang.NullPointerException
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2596)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2621)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at android.app.ActivityThread.access$2200(ActivityThread.java:126)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1932)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at android.os.Handler.dispatchMessage(Handler.java:99)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at android.os.Looper.loop(Looper.java:123)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at android.app.ActivityThread.main(ActivityThread.java:4595)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at java.lang.reflect.Method.invokeNative(Native Method)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at java.lang.reflect.Method.invoke(Method.java:521)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at dalvik.system.NativeStart.main(Native Method)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): Caused by: java.lang.NullPointerException
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at com.droidnova.android.howto.optionmenu.Test.onCreate(Test.java:37)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2544)
05-02 19:51:56.538: ERROR/AndroidRuntime(20788): ... 11 more
05-02 19:51:58.658: ERROR/ActivityManager(97): fail to set top app changed!
05-02 19:55:31.438: ERROR/AndroidRuntime(20809): ERROR: thread attach failed
05-02 19:55:38.148: ERROR/AndroidRuntime(20820): ERROR: thread attach failed
05-02 19:55:41.638: ERROR/PackageInstallationReceiver(248): Remove /data/local/tmp/com.droidnova.android.howto.optionmenu.apk Fail!
05-02 20:15:28.608: ERROR/wpa_supplicant(139): Set_key: Wrong Key
05-02 20:15:28.608: ERROR/wpa_supplicant(139): Set_key: Wrong Key
05-02 20:15:28.608: ERROR/wpa_supplicant(139): Set_key: Wrong Key
05-02 20:15:28.608: ERROR/wpa_supplicant(139): Set_key: Wrong Key
05-02 20:15:28.608: ERROR/wpa_supplicant(139): Set_key: Wrong Key
05-02 20:15:29.648: ERROR/wpa_supplicant(139): prepare_filter_struct: type=5
05-02 20:15:32.728: ERROR/wpa_supplicant(139): prepare_filter_struct: type=5
此处更详细的是测试类
public class Test extends ListActivity {
Prefs myprefs = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.listplaceholder);
ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>();
JSONObject json = JSONfunctions.getJSONfromURL("http://midsweden.gofreeserve.com/fetch.php?identifier="
+ Test.this.myprefs.getEmail());
try{
JSONArray earthquakes = json.getJSONArray("earthquakes");
for(int i=0;i<earthquakes.length();i++){
HashMap<String, String> map = new HashMap<String, String>();
JSONObject e = earthquakes.getJSONObject(i);
map.put("id", String.valueOf(i));
map.put("name", "Earthquake name:" + e.getString("name"));
map.put("password", "Magnitude: " + e.getString("password"));
mylist.add(map);
}
}catch(JSONException e) {
Log.e("log_tag", "Error parsing data "+e.toString());
}
ListAdapter adapter = new SimpleAdapter(this, mylist , R.layout.test,
new String[] { "name", "magnitude" },
new int[] { R.id.item_title, R.id.item_subtitle });
setListAdapter(adapter);
final ListView lv = getListView();
lv.setTextFilterEnabled(true);
lv.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
@SuppressWarnings("unchecked")
HashMap<String, String> o = (HashMap<String, String>) lv.getItemAtPosition(position);
Toast.makeText(Test.this, "ID '" + o.get("id") + "' was clicked.", Toast.LENGTH_SHORT).show();
}
});
}
这是分享偏好类
package com.droidnova.android.howto.optionmenu;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
public class Prefs {
private SharedPreferences _prefs = null;
private Editor _editor = null;
private String _useremailaddress = "Unknown";
private String _serverurl = "http://chinar.gofreeserve.com/db.php";
public Prefs(Context context) {
this._prefs = context.getSharedPreferences("PREFS_PRIVATE", Context.MODE_PRIVATE);
this._editor = this._prefs.edit();
}
public String getValue(String key, String defaultvalue) {
if (this._prefs == null) {
return "Unknown";
}
return this._prefs.getString(key, defaultvalue);
}
public void setValue(String key, String value) {
if (this._editor == null) {
return;
}
this._editor.putString(key, value);
}
public String getEmail() {
if (this._prefs == null) {
return "Unknown";
}
this._useremailaddress = this._prefs.getString("emailaddress", "noidea");
return this._useremailaddress;
}
public String getServer() {
if (this._prefs == null) {
return "http://chinar.gofreeserve.com";
}
this._serverurl = this._prefs.getString("serverurl", "http://chinar.gofreeserve.com/");
return this._serverurl;
}
public void setEmail(String newemail) {
if (this._editor == null) {
return;
}
this._editor.putString("emailaddress", newemail);
}
public void setServer(String serverurl) {
if (this._editor == null) {
return;
}
this._editor.putString("serverurl", serverurl);
}
public void save() {
if (this._editor == null) {
return;
}
this._editor.commit();
}
}
答案 0 :(得分：2)
您收到NullPointerException，因为（很可能）您的myprefs为空。
您在哪里初始化此字段？
无论如何，为了保存引用，您应该查看Shared Preferences而不是创建自己的解决方案。
答案 1 :(得分：1)
myPrefs var为null
public class Test extends ListActivity {
Prefs myprefs = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.listplaceholder);
ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>();
//myprefs can only be null at this point, you need this line or an equivalent for your Prefs class:
myprefs = PreferenceManager.getDefaultSharedPreferences(this);
JSONObject json = JSONfunctions.getJSONfromURL("http://midsweden.gofreeserve.com/fetch.php?identifier="
+ Test.this.myprefs.getEmail());
API：
或
修改的
啊，是的，你使用了一些自定义首选项类，所以你必须实例化这个类。
// Your choice of
Prefs myprefs = new Prefs();
Prefs myprefs = new Prefs(this);
Prefs myprefs = new Prefs(getApplicationContext());
或者如果他想要使用的方法是静态的：
Prefs.getEmail();
请仔细阅读：Top Ten Java Errors（ 10号和1号！）
答案 2 :(得分：0)
您的代码中有一个空指针异常：
Caused by: java.lang.NullPointerException
05-02 19:49:53.688: ERROR/AndroidRuntime(20721): at com.droidnova.android.howto.optionmenu.Test.onCreate(Test.java:37)
修复此问题，至少应用程序将运行。