我已经开始学习Android应用程序开发了，我可以说我已经了解了布局如何与源文件进行通信。但是，我很快就失望了。尽管Java语言很自然，但Java中的简单任务对我来说非常复杂。
我想在ListView中显示来自JSON响应的图像。这是我的主要目的。
我想我有两个选择：AsyncTasks方式，或Google Volley。我想使用Google Volley，因为它看起来更容易，但我没有找到任何示例获取和显示一堆图像。我不知道我是否应该关心缓存内容。我在谈论10个GIF动画。稍后，当我向下滚动时，我需要刷新它们，从响应中读取分页数据。我应该阅读this。
This就是我一直在研究的例子。
我将其粘贴到此处，但最好在上面的链接中查看完整的示例，
public class FetchWeatherTask extends AsyncTask<String, Void, String[]> {
private final String LOG_TAG = FetchWeatherTask.class.getSimpleName();
/* The date/time conversion code is going to be moved outside the asynctask later,
* so for convenience we're breaking it out into its own method now.
*/
private String getReadableDateString(long time){
// Because the API returns a unix timestamp (measured in seconds),
// it must be converted to milliseconds in order to be converted to valid date.
Date date = new Date(time * 1000);
SimpleDateFormat format = new SimpleDateFormat("E, MMM d");
return format.format(date).toString();
}
/**
* Prepare the weather high/lows for presentation.
*/
private String formatHighLows(double high, double low) {
// For presentation, assume the user doesn't care about tenths of a degree.
long roundedHigh = Math.round(high);
long roundedLow = Math.round(low);
String highLowStr = roundedHigh + "/" + roundedLow;
return highLowStr;
}
/**
* Take the String representing the complete forecast in JSON Format and
* pull out the data we need to construct the Strings needed for the wireframes.
*
* Fortunately parsing is easy: constructor takes the JSON string and converts it
* into an Object hierarchy for us.
*/
private String[] getWeatherDataFromJson(String forecastJsonStr, int numDays)
throws JSONException {
// These are the names of the JSON objects that need to be extracted.
final String OWM_LIST = "list";
final String OWM_WEATHER = "weather";
final String OWM_TEMPERATURE = "temp";
final String OWM_MAX = "max";
final String OWM_MIN = "min";
final String OWM_DATETIME = "dt";
final String OWM_DESCRIPTION = "main";
JSONObject forecastJson = new JSONObject(forecastJsonStr);
JSONArray weatherArray = forecastJson.getJSONArray(OWM_LIST);
String[] resultStrs = new String[numDays];
for(int i = 0; i < weatherArray.length(); i++) {
// For now, using the format "Day, description, hi/low"
String day;
String description;
String highAndLow;
// Get the JSON object representing the day
JSONObject dayForecast = weatherArray.getJSONObject(i);
// The date/time is returned as a long. We need to convert that
// into something human-readable, since most people won't read "1400356800" as
// "this saturday".
long dateTime = dayForecast.getLong(OWM_DATETIME);
day = getReadableDateString(dateTime);
// description is in a child array called "weather", which is 1 element long.
JSONObject weatherObject = dayForecast.getJSONArray(OWM_WEATHER).getJSONObject(0);
description = weatherObject.getString(OWM_DESCRIPTION);
// Temperatures are in a child object called "temp". Try not to name variables
// "temp" when working with temperature. It confuses everybody.
JSONObject temperatureObject = dayForecast.getJSONObject(OWM_TEMPERATURE);
double high = temperatureObject.getDouble(OWM_MAX);
double low = temperatureObject.getDouble(OWM_MIN);
highAndLow = formatHighLows(high, low);
resultStrs[i] = day + " - " + description + " - " + highAndLow;
}
return resultStrs;
}
@Override
protected String[] doInBackground(String... params) {
// If there's no zip code, there's nothing to look up. Verify size of params.
if (params.length == 0) {
return null;
}
// These two need to be declared outside the try/catch
// so that they can be closed in the finally block.
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
// Will contain the raw JSON response as a string.
String forecastJsonStr = null;
String format = "json";
String units = "metric";
int numDays = 7;
try {
// Construct the URL for the OpenWeatherMap query
// Possible parameters are avaiable at OWM's forecast API page, at
// http://openweathermap.org/API#forecast
final String FORECAST_BASE_URL =
"http://api.openweathermap.org/data/2.5/forecast/daily?";
final String QUERY_PARAM = "q";
final String FORMAT_PARAM = "mode";
final String UNITS_PARAM = "units";
final String DAYS_PARAM = "cnt";
Uri builtUri = Uri.parse(FORECAST_BASE_URL).buildUpon()
.appendQueryParameter(QUERY_PARAM, params[0])
.appendQueryParameter(FORMAT_PARAM, format)
.appendQueryParameter(UNITS_PARAM, units)
.appendQueryParameter(DAYS_PARAM, Integer.toString(numDays))
.build();
URL url = new URL(builtUri.toString());
// Create the request to OpenWeatherMap, and open the connection
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();
// Read the input stream into a String
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
if (inputStream == null) {
// Nothing to do.
return null;
}
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
// Since it's JSON, adding a newline isn't necessary (it won't affect parsing)
// But it does make debugging a *lot* easier if you print out the completed
// buffer for debugging.
buffer.append(line + "\n");
}
if (buffer.length() == 0) {
// Stream was empty. No point in parsing.
return null;
}
forecastJsonStr = buffer.toString();
} catch (IOException e) {
Log.e(LOG_TAG, "Error ", e);
// If the code didn't successfully get the weather data, there's no point in attemping
// to parse it.
return null;
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
if (reader != null) {
try {
reader.close();
} catch (final IOException e) {
Log.e(LOG_TAG, "Error closing stream", e);
}
}
}
try {
return getWeatherDataFromJson(forecastJsonStr, numDays);
} catch (JSONException e) {
Log.e(LOG_TAG, e.getMessage(), e);
e.printStackTrace();
}
// This will only happen if there was an error getting or parsing the forecast.
return null;
}
@Override
protected void onPostExecute(String[] result) {
if (result != null) {
mForecastAdapter.clear();
for(String dayForecastStr : result) {
mForecastAdapter.add(dayForecastStr);
}
// New data is back from the server. Hooray!
}
}
}
这是我的JSON响应的一个例子，
"data": {
"type": "gif",
"id": "feqkVgjJpYtjy",
"url": "http:\/\/giphy.com\/gifs\/feqkVgjJpYtjy",
"bitly_gif_url": "http:\/\/gph.is\/XJ200y",
"bitly_url": "http:\/\/gph.is\/XJ200y",
"embed_url": "http:\/\/giphy.com\/embed\/feqkVgjJpYtjy",
"username": "",
"source": "http:\/\/littleanimalgifs.tumblr.com\/post\/17994517807",
"rating": "g",
"caption": "",
"content_url": "",
"trending_datetime": "2014-09-23 22:49:53",
"images": {
"fixed_height": {
"url": "http:\/\/media4.giphy.com\/media\/feqkVgjJpYtjy\/200.gif",
"width": "445",
"height": "200",
"mp4": "http:\/\/media.giphy.com\/media\/feqkVgjJpYtjy\/200.mp4"
},
"fixed_height_still": {
"url": "http:\/\/media4.giphy.com\/media\/feqkVgjJpYtjy\/200_s.gif",
"width": "445",
"height": "200"
},
"fixed_height_downsampled": {
"url": "http:\/\/media4.giphy.com\/media\/feqkVgjJpYtjy\/200_d.gif",
"width": "445",
"height": "200"
},
"fixed_width": {
"url": "http:\/\/media4.giphy.com\/media\/feqkVgjJpYtjy\/200w.gif",
"width": "200",
"height": "90",
"mp4": "http:\/\/media.giphy.com\/media\/feqkVgjJpYtjy\/200w.mp4"
},
"fixed_width_still": {
"url": "http:\/\/media4.giphy.com\/media\/feqkVgjJpYtjy\/200w_s.gif",
"width": "200",
"height": "90"
},
"fixed_width_downsampled": {
"url": "http:\/\/media4.giphy.com\/media\/feqkVgjJpYtjy\/200w_d.gif",
"width": "200",
"height": "90"
},
"downsized": {
"url": "http:\/\/media4.giphy.com\/media\/feqkVgjJpYtjy\/giphy.gif",
"width": "334",
"height": "150",
"size": "511581"
},
"downsized_still": {
"url": "http:\/\/media4.giphy.com\/media\/feqkVgjJpYtjy\/giphy_s.gif",
"width": "334",
"height": "150"
},
"original": {
"url": "http:\/\/media4.giphy.com\/media\/feqkVgjJpYtjy\/giphy.gif",
"width": "334",
"height": "150",
"size": "511581",
"frames": "27",
"mp4": "http:\/\/media.giphy.com\/media\/feqkVgjJpYtjy\/giphy.mp4"
},
"original_still": {
"url": "http:\/\/media4.giphy.com\/media\/feqkVgjJpYtjy\/giphy_s.gif",
"width": "334",
"height": "150"
}
}
},
"meta": {
"status": 200,
"msg": "OK"
}
我不需要解决它，但想要得到这个想法。