【发布时间】：2016-03-24 12:34:47
【问题描述】：
我正在开发一个从服务器获取图像并下载它们并将它们插入到 GridView 布局中的 android 应用程序。 我从中获取数据的服务器是电影数据库https://www.themoviedb.org/ 假设发送具有特定 URL 的服务器作为 http://api.themoviedb.org/3/movie/popular?api_key=2add2d45d1265781502d4d7c2f9f67c2 将使服务器向我发送最流行电影的海报（图像）流，然后我将解析 JSON 响应并在网格视图中显示图像 这是我的文件.... 1)MainActivity.java
public class MainActivity extends Activity {
private static final String TAG = MainActivity.class.getSimpleName();
private GridView mGridView;
private ProgressBar mProgressBar;
private ImageAdapter mGridAdapter;
private ArrayList<GridItem> mGridData;
private String FEED_URL = "http://api.themoviedb.org/3/discover/movie?sort_by=popularity.desc&api_key=2add2d45d1265781502d4d7c2f9f67c2";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mGridView = (GridView) findViewById(R.id.grid_view);
mProgressBar = (ProgressBar) findViewById(R.id.progressBar);
mGridData = new ArrayList();
mGridAdapter = new ImageAdapter(this, R.layout.grid_item, mGridData);
mGridView.setAdapter(mGridAdapter);
//Start download
new AsyncHttpTask().execute(FEED_URL);
mProgressBar.setVisibility(View.VISIBLE);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
//Downloading data asynchronously
public class AsyncHttpTask extends AsyncTask<String, Void, Integer> {
@Override
protected Integer doInBackground(String... params) {
Integer result = 0;
try {
// Create Apache HttpClient
HttpClient httpclient = new DefaultHttpClient();
HttpResponse httpResponse = httpclient.execute(new HttpGet(params[0]));
int statusCode = httpResponse.getStatusLine().getStatusCode();
// 200 represents HTTP OK
if (statusCode == 200) {
String response = streamToString(httpResponse.getEntity().getContent());
parseResult(response);
result = 1; // Successful
} else {
result = 0; //"Failed
}
} catch (Exception e) {
Log.d(TAG, e.getLocalizedMessage());
}
return result;
}
@Override
protected void onPostExecute(Integer result) {
// Download complete. Lets update UI
if (result == 1) {
mGridAdapter.setGridData(mGridData);
} else {
Toast.makeText(MainActivity.this, "network error", Toast.LENGTH_SHORT).show();
}
//Hide progressbar
mProgressBar.setVisibility(View.GONE);
}
}
String streamToString(InputStream stream) throws IOException {
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(stream));
String line;
String result = "";
while ((line = bufferedReader.readLine()) != null) {
result += line;
}
// Close stream
if (null != stream) {
stream.close();
}
return result;
}
/**
* Parsing the feed results and get the list
*
* @param result
*/
private void parseResult(String result) {
try {
JSONObject response = new JSONObject(result);
JSONArray posts = response.optJSONArray("posts");
GridItem item;
for (int i = 0; i < posts.length(); i++) {
JSONObject post = posts.optJSONObject(i);
item = new GridItem();
JSONArray attachments = post.getJSONArray("attachments");
if (null != attachments && attachments.length() > 0) {
JSONObject attachment = attachments.getJSONObject(0);
if (attachment != null)
item.setImage(attachment.getString("url"));
}
mGridData.add(item);
}
} catch (JSONException e) {
e.printStackTrace();
}
}}
2)GridItem.java
public class GridItem {
private String image;
public GridItem() {
super();
}
public String getImage() {
return image;
}
public void setImage(String image) {
this.image = image;
}
}
3)ImageAdapter.java
public class ImageAdapter extends ArrayAdapter<GridItem> {
private Context mContext;
private int layoutResourceId;
private ArrayList<GridItem> mGridData = new ArrayList<GridItem>();
public ImageAdapter(Context mContext, int layoutResourceId, ArrayList<GridItem> mGridData) {
super(mContext, layoutResourceId, mGridData);
this.layoutResourceId = layoutResourceId;
this.mContext = mContext;
this.mGridData = mGridData;
}
public void setGridData(ArrayList<GridItem> mGridData) {
this.mGridData = mGridData;
notifyDataSetChanged();
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View row = convertView;
ViewHolder holder;
if (row == null) {
LayoutInflater inflater = ((Activity) mContext).getLayoutInflater();
row = inflater.inflate(layoutResourceId, parent, false);
holder = new ViewHolder();
holder.imageView = (ImageView) row.findViewById(R.id.grid_item_image);
row.setTag(holder);
} else {
holder = (ViewHolder) row.getTag();
}
GridItem item = mGridData.get(position);
Picasso.with(mContext).load(item.getImage()).into(holder.imageView);
return row;
}
static class ViewHolder {
ImageView imageView;
}}
4)activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MainActivity">
<GridView
android:id="@+id/grid_view"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:columnWidth="100dp"
android:drawSelectorOnTop="true"
android:gravity="center"
android:numColumns="auto_fit"
android:stretchMode="columnWidth"
android:verticalSpacing="5dp"
android:focusable="true"
android:clickable="true"/>
<ProgressBar
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/progressBar"
android:layout_centerInParent="true"
android:visibility="gone"/>
5)Grid_item.xml
<?xml version="1.0" encoding="utf-8"?>
<ImageView
android:layout_width="300dp"
android:layout_height="300dp"
android:id="@+id/grid_item_image"
android:scaleType="centerCrop" />
当我运行应用程序时它崩溃并说“不幸的是应用程序已停止” 我调试了代码，它在 log cat 中显示了这个错误消息
03-24 14:51:05.074 5099-5145/com.example.android.movieguide E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
Process: com.example.android.movieguide, PID: 5099
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:300)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
Caused by: java.lang.NullPointerException: println needs a message
at android.util.Log.println_native(Native Method)
at android.util.Log.d(Log.java:158)
at com.example.android.movieguide.MainActivity$AsyncHttpTask.doInBackground(MainActivity.java:91)
at com.example.android.movieguide.MainActivity$AsyncHttpTask.doInBackground(MainActivity.java:71)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
在 android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 在 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 在 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 在 java.lang.Thread.run(Thread.java:841)
【问题讨论】：
-
可以添加完整的错误日志吗？
-
在问题文本中发布您的 API 密钥可能不是一个好主意..
-
请发布您收到的错误代码，以便我们修复它。
-
您的回复中没有带有键
posts的 JSONArray。 -
好的，我会更新问题