我正在解析来自天气提要的 JSON 响应，并且我收到的数据包括与条件相对应的图标的 URL，然后我在 ImageView 中显示该图标。在将代码包移动到我的项目中之前，我能够在沙盒应用程序中完成这项工作。
在主项目中，我使用最新版本的ActionBarSherlock和SlidingMenu进行导航，这两个应用程序都使用了Android-Async-Http-Client但现在它在尝试在 ImageView 中显示来自该 url 的图标时出现致命的 NullPointerException。我不认为这是由任何库引起的。
我已经看到滑动菜单主要由某种类型的 ListView 组成，它使用适配器处理，我在滑动菜单的一部分中正在这样做。但我唯一的线索是它崩溃了，因为现在它是我正在尝试使用的屏幕外 UI 元素。我的滑动菜单中有一些不是由适配器处理的东西有关系吗？我无法想象还有什么不同，但也许你们对我缺少什么有所了解。希望这不是我刚刚忘记的基本内容……或者也许是:)
好的，谢谢你的任何想法。
public class MainActivity extends SlidingActivity implements
ActionBar.OnNavigationListener {
final String TAG = "MainActivity";
private TextView mSelected;
private String[] mLocations;
ImageLoader imageLoader;
ImageView weatherIcon;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
imageLoader = new ImageLoader(this);
wireViews();
getWeatherFeed();
Context context = getSupportActionBar().getThemedContext();
ArrayAdapter<CharSequence> list = ArrayAdapter.createFromResource(
context, R.array.activities, R.layout.sherlock_spinner_item);
list.setDropDownViewResource(R.layout.sherlock_spinner_dropdown_item);
getSupportActionBar().setNavigationMode(ActionBar.NAVIGATION_MODE_LIST);
getSupportActionBar().setListNavigationCallbacks(list, this);
getSupportActionBar().setDisplayShowTitleEnabled(false);
// set the Behind View
setBehindContentView(R.layout.menu_frame);
// SlidingMenu
SlidingMenu sm = getSlidingMenu();
sm.setShadowWidthRes(R.dimen.shadow_width);
sm.setShadowDrawable(R.drawable.shadow);
sm.setBehindOffsetRes(R.dimen.slidingmenu_offset);
sm.setFadeDegree(0.35f);
sm.setTouchModeAbove(SlidingMenu.TOUCHMODE_FULLSCREEN);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
setSlidingActionBarEnabled(false);
ListView menuList = (ListView) findViewById(R.id.menuList);
SlidingMenuItem[] data = new SlidingMenuItem[] {
new SlidingMenuItem("Item1 Label", "Item1 Sub-label",getResources().getDrawable(R.drawable.item1)),
new SlidingMenuItem("Item2 Label", "Item2 Sub-Label",getResources().getDrawable(R.drawable.item2)) };
MenuAdapter adapter = new MenuAdapter(this, R.layout.sliding_menu_item,
data);
menuList.setAdapter(adapter);
}
private void updateWeatherUi(String degreeText, String descriptionText,
String iconUrl) {
Log.i(TAG, "Updating UI elements...");
if (imageLoader != null) {
Log.i(TAG, "IMAGE_LOADER NOT NULL!!!");
}
imageLoader.DisplayImage(iconUrl, weatherIcon); // FIXME: FATAL CRASH HERE !!!
}
/** Build a Weather object from the JSON response.
* @throws JSONException */
private void buildWeatherObject(String rawResponse) throws JSONException {
Log.i(TAG, "Building Weather ojbect...");
JSONObject baseObject = new JSONObject(rawResponse);
JSONObject data = new JSONObject(baseObject.getString(Key.DATA));
JSONArray conditionArray = new JSONArray(
data.getString(Key.CURRENT_CONDITION));
for (int i = 0; i < conditionArray.length(); i++) {
JSONObject conditionElement = new JSONObject(
conditionArray.getString(i));
weather = new Weather();
weather.tempMaxF = conditionElement.getString(Key.TEMP_F);
JSONArray weatherDescriptionArray = new JSONArray(
conditionElement.getString(Key.W_WEATHER_DESC));
for (int j = 0; j < weatherDescriptionArray.length(); j++) {
JSONObject weatherDescriptionElement = new JSONObject(
weatherDescriptionArray.getString(j));
weather.weatherDesc = weatherDescriptionElement
.getString(Key.VALUE);
}
JSONArray weatherIconArray = new JSONArray(
conditionElement.getString(Key.WEATHER_ICON_URL));
for (int j = 0; j < weatherIconArray.length(); j++) {
JSONObject weatherIconElement = new JSONObject(
weatherIconArray.getString(j));
weather.weatherIconUrl = weatherIconElement
.getString(Key.VALUE);
Log.i(TAG, weather.weatherIconUrl);
}
conditionElement = null;
updateWeatherUi(weather.tempMaxF, weather.weatherDesc,
weather.weatherIconUrl);
}
}
/** Asynchronously request and receive weather feed data. */
private void getWeatherFeed() {
Log.i(TAG, "Getting asynchronous JSON feed...");
AsyncHttpClient client = new AsyncHttpClient();
client.get(WEATHER_FEED_URL, new AsyncHttpResponseHandler() {
@Override
public void onSuccess(String response) {
try {
buildWeatherObject(response);
} catch (JSONException e) {
e.printStackTrace();
}
}
@Override
public void onFailure(Throwable arg0, String arg1) {
super.onFailure(arg0, arg1);
showToast("Sorry, the weather forecast wasn't available just then.");
}
});
}
private void wireViews() {
Log.i(TAG, "Wiring UI elements...");
mSelected = (TextView) findViewById(R.id.text);
mLocations = getResources().getStringArray(R.array.activities);
weatherIcon = (ImageView) findViewById(R.id.weatherIconView);
}
12-21 01:01:11.130: I/MainActivity(28502): Building Weather ojbect...
12-21 01:01:11.170: I/MainActivity(28502): http://www.worldweatheronline.com/images/wsymbols01_png_64/wsymbol_0001_sunny.png
12-21 01:01:11.170: I/MainActivity(28502): Updating UI elements...
12-21 01:01:11.170: I/MainActivity(28502): IMAGE_LOADER NOT NULL!!!
12-21 01:01:11.170: D/AndroidRuntime(28502): Shutting down VM
12-21 01:01:11.170: W/dalvikvm(28502): threadid=1: thread exiting with uncaught exception (group=0x4001d5a0)
12-21 01:01:11.180: E/AndroidRuntime(28502): FATAL EXCEPTION: main
12-21 01:01:11.180: E/AndroidRuntime(28502): java.lang.NullPointerException
12-21 01:01:11.180: E/AndroidRuntime(28502): at com.eric.app.networkxml.ImageLoader.DisplayImage(ImageLoader.java:42)
12-21 01:01:11.180: E/AndroidRuntime(28502): at com.eric.app.MainActivity.updateWeatherUi(MainActivity.java:129)
12-21 01:01:11.180: E/AndroidRuntime(28502): at com.eric.app.MainActivity.buildWeatherObject(MainActivity.java:172)
12-21 01:01:11.180: E/AndroidRuntime(28502): at com.eric.app.MainActivity.access$0(MainActivity.java:137)
12-21 01:01:11.180: E/AndroidRuntime(28502): at com.eric.app.MainActivity$1.onSuccess(MainActivity.java:195)
12-21 01:01:11.180: E/AndroidRuntime(28502): at com.loopj.android.http.AsyncHttpResponseHandler.handleSuccessMessage(AsyncHttpResponseHandler.java:160)
12-21 01:01:11.180: E/AndroidRuntime(28502): at com.loopj.android.http.AsyncHttpResponseHandler.handleMessage(AsyncHttpResponseHandler.java:173)
12-21 01:01:11.180: E/AndroidRuntime(28502): at com.loopj.android.http.AsyncHttpResponseHandler$1.handleMessage(AsyncHttpResponseHandler.java:85)
12-21 01:01:11.180: E/AndroidRuntime(28502): at android.os.Handler.dispatchMessage(Handler.java:99)
12-21 01:01:11.180: E/AndroidRuntime(28502): at android.os.Looper.loop(Looper.java:150)
12-21 01:01:11.180: E/AndroidRuntime(28502): at android.app.ActivityThread.main(ActivityThread.java:4263)
12-21 01:01:11.180: E/AndroidRuntime(28502): at java.lang.reflect.Method.invokeNative(Native Method)
12-21 01:01:11.180: E/AndroidRuntime(28502): at java.lang.reflect.Method.invoke(Method.java:507)
12-21 01:01:11.180: E/AndroidRuntime(28502): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
12-21 01:01:11.180: E/AndroidRuntime(28502): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
12-21 01:01:11.180: E/AndroidRuntime(28502): at dalvik.system.NativeStart.main(Native Method)
哎呀！我试图发布一个“片段”，但也许我应该发布完整的文件......