我已经制作了一个gridview，我试图在该网格中添加下一个功能。当有人点击"下一步"时，网格就会加载一堆新的图像。
我已经做了一个逻辑，不知何故它是工作的，但它是不稳定的。应用程序有时会停止，有时点击"下一步"下一页被跳过(假设目前我在第0页，当我点击"下一步"网格得到刷新，第2页显示，而不是第1页)
我正在做的是我做了一个asynctask，它发送http请求到php服务器的图像的新url。然后刷新gridview并显示来自新图像url的新图像。
public class UserPage extends Activity {
ImageAdapter ia = new ImageAdapter(this);
GetResponse task = new GetResponse(0);
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.userpage);
final GridView gridview = (GridView) findViewById(R.id.gridview);
gridview.setAdapter(ia);
gridview.setStretchMode(GridView.STRETCH_COLUMN_WIDTH);
Button nxt = (Button) findViewById(R.id.nextbuttongrid);
nxt.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// next page
int i = Integer.parseInt(GetResponse.counter);
i=i+1;
GetResponse.counter = Integer.toString(i);
String x = GetResponse.response;
task.execute();
//this is done so that the thread sleeps until the response variable value is updated
while(x.equals(GetResponse.response)==true){
try {
Thread.sleep(50);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("Here in sleep..incre");
} }
change(gridview);
}
});
Button pre = (Button) findViewById(R.id.previousbuttongrid);
pre.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// previous page
int i = Integer.parseInt(GetResponse.counter);
i=i-1;
GetResponse.counter = Integer.toString(i);
String x = GetResponse.response;
task.execute();
//this is done so that the thread sleeps until the response variable value is updated
while(x.equals(GetResponse.response)==true){
try {
Thread.sleep(50);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("Here in sleep.. decre");
} }
change(gridview);
}
});
/**
* On Click event for Single Gridview Item
* */
gridview.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View v,
int position, long id) {
// Sending image id to FullImage.java
Intent i = new Intent(getApplicationContext(), FullImage.class);
i.putExtra("id", position);
startActivity(i);
}
});
}
void change(GridView gridview) {
ia = new ImageAdapter(this);
gridview.invalidateViews();
gridview.setAdapter(ia);
}
}
public class GetResponse extends AsyncTask<Void, Void, Void> {
public static String counter = "0";
HttpPost httppost;
StringBuffer buffer;
HttpResponse response1;
HttpClient httpclient;
List<NameValuePair> nameValuePairs;
public static String response;
@Override
protected Void doInBackground(Void... params) {
try {
Log.d("response's Value == >", "Response previous " + response);
httpclient=new DefaultHttpClient();
httppost= new HttpPost(ServerAdressHere);
//add your data
nameValuePairs = new ArrayList<NameValuePair>(3);
nameValuePairs.add(new BasicNameValuePair("username",AndroidPHPConnectionDemo.userName));
nameValuePairs.add(new BasicNameValuePair("password",AndroidPHPConnectionDemo.passWord));
nameValuePairs.add(new BasicNameValuePair("count",counter));
Log.d("Counter's Value == >", "Counter " + counter);
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
//Execute HTTP Post Request
response1=httpclient.execute(httppost);
ResponseHandler<String> responseHandler = new BasicResponseHandler();
response = httpclient.execute(httppost, responseHandler);
Log.d("response's Value == >", "Response after " + response);
}
catch(Exception e){
System.out.println("Exception Here"+e);
}
return null;
}
}
public class ImageAdapter extends BaseAdapter {
private Context mContext;
private TextView txtUrl;
private String response;
public ImageView imageView;
public static String[] mThumbIds;
public ImageAdapter(Context c) {
mContext = c;
this.response = GetResponse.response.trim();
mThumbIds = response.split(",");
}
private final Downloader imageDownloader = new Downloader(mContext);
public int getCount() {
return mThumbIds.length;
}
public Object getItem(int position) {
return mThumbIds[position];
}
public long getItemId(int position) {
return mThumbIds[position].hashCode();
}
// create a new ImageView for each item referenced by the Adapter
public View getView(int position, View convertView, ViewGroup parent) {
if(convertView==null) {
imageView = new ImageView(mContext);
imageView.setLayoutParams(new GridView.LayoutParams(LayoutParams.MATCH_PARENT, 195));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(10, 10, 10, 10);
}
else {
imageView = (ImageView) convertView;
}
imageDownloader.DisplayImage(mThumbIds[position], (ImageView) imageView);
return imageView;
}
public Downloader getImageDownloader() {
return imageDownloader;
}
}
"counter"变量(静态和字符串类型)在请求中发送，它告诉php服务器下一个gridview的页码。因此，服务器将发送与该页码绑定的图像url。
我面临的问题是，网格得到刷新之前"响应"变量是由asynctask类更新。所以这就是为什么我使用System.sleep()来获得两行代码执行的时间间隔。
"response"变量(静态和整型)包含图像的url。
请帮忙!如果需要更多细节，请询问。
首先，线程。onClick方法中的sleep in循环不是一种正确的方法。异步任务的重点是避免锁定主线程和线程。睡眠就是这样做的。
使用asynctask的onPostExecute来代替。
然而，这显然工作到目前为止(你的服务器和连接是足够快，否则你会有一个ANR)，即使你的ui可能冻结几秒钟。
之后，就是图片下载的问题了。调用setAdapter(new Adapter…)似乎是一个足够好的方法。
一步一步调试你做了多少?
- 您是否收到
Log.d("response's Value == >", "Response after " + response);行的图像id列表? - 你到达getView，如果是这样你得到正确的url/id/字符串，无论应该是在mThumbIds[位置]?
- 如果是，什么是下载程序，它是如何工作的?
出于好奇，为什么要执行两次请求?(response1=httpclient.execute(httppost);)
编辑
我真不敢相信你没有，尽管提到你的应用程序实际上崩溃了，这很有趣，这与"网格没有得到刷新"是完全不同的。
A/read你的堆栈跟踪。
B/如果不清楚，谷歌一下。
C/我不知道还有什么可以添加到(a task can be executed only once)