我创建了一个列表字段，其中包含一张图片和一行中的一些数据 我从 Json 获得的图片和数据。我的代码正在运行，但在获取列表后我的用户界面挂起， 有两个步骤 1)从json中解析出数据和图片URL 2) 并显示在列表字段中 我将在下面发布我的代码和列表的屏幕截图
public final class MyScreen extends MainScreen implements ListFieldCallback
{
HttpConnection httpConn;
int responseCode;
private static ListField _list;
private static Vector listElements = new Vector();
private static Vector elements = new Vector();
private static Vector contentelements = new Vector();
private static Vector datelements = new Vector();
private static Vector Imageselements = new Vector();
LabelField label;
String imagename;
Bitmap bit ;
Connection connectionthread;
public MyScreen()
{
// Set the displayed title of the screen
//setTitle("MyTitle");
_list = new ListField();
_list.invalidate();
_list.setEmptyString("please wait..", DrawStyle.HCENTER);
_list.setRowHeight(100);
_list.setCallback(this);
add(_list);
connectionthread = new Connection();
connectionthread.start();
}
public class Connection extends Thread{
public void run() {
try {
String httpURL = "http://192.168.1.91/bjp_app/program"+ getConnectionString();
httpConn = (HttpConnection) Connector.open(httpURL);
httpConn.setRequestMethod(HttpConnection.GET);
responseCode = httpConn.getResponseCode();
if (responseCode != HttpConnection.HTTP_OK)
{
throw new IOException("HTTP response code: "+ responseCode);
//System.out.println("\n Internaet problem HttpConnection. = "+responseCode);
}else{
System.out.println("\n elseeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee= ");
System.out.println("\nHttpConnection.HTTP_OK = "+responseCode);
DataOutputStream _outStream = new DataOutputStream(httpConn.openDataOutputStream());
byte[] request_body = httpURL.getBytes();
for (int i = 0; i < request_body.length; i++) {
_outStream.writeByte(request_body[i]);
}
DataInputStream _inputStream = new DataInputStream(
httpConn.openInputStream());
StringBuffer _responseMessage = new StringBuffer();
int ch;
while ((ch = _inputStream.read()) != -1) {
_responseMessage.append((char) ch);
}
String res = (_responseMessage.toString());
String responce = res.trim();
System.out.println("\nresponce= "+responce);
JSONArray jsnarry = new JSONArray(responce);
System.out.println("\n--length----- "+jsnarry.length());
for (int i = 0; i < jsnarry.length(); i++){
JSONArray inerarray = jsnarry.getJSONArray(i);
System.out.println("\n-innerarray-length----- "+inerarray.length());
//for (int i1 = 0; i1 < inerarray.length(); i1++) {
//System.out.println("\n-inerarray-values----- "+inerarray.getString(i1));
String ID = inerarray.getString(0);
String TITTLE = inerarray.getString(1);
String CONTENT = inerarray.getString(2);
String DATE = inerarray.getString(3);
String IMAGE = inerarray.getString(4);
String six = inerarray.getString(5);
System.out.println("................................................");
System.out.println("ID= "+ID);
System.out.println("TITTLE= "+TITTLE);
System.out.println("CONTENT= "+CONTENT);
System.out.println("DATE= "+DATE);
System.out.println("IMAGE= "+IMAGE);
imagename = "http://sanjaytandon.in/admin/image/"+IMAGE.trim();
System.out.println("imagename= "+imagename);
//System.out.println("six "+six);
System.out.println("....................................................=");
// String jsonresponse = ""+inerarray.getString(i1);
//label = new LabelField(jsonresponse,LabelField.FOCUSABLE);
//add(label);
//}
elements.addElement(TITTLE);
contentelements.addElement(CONTENT);
datelements.addElement(DATE);
Imageselements.addElement(imagename);
}
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
try {
_list.setSize(elements.size());
_list.setSize(contentelements.size());
_list.setSize(datelements.size());
_list.setSize(Imageselements.size());
//invalidate();
} catch (Exception e) {
// TODO Auto-generated catch block
System.out.println("error _list.setSize"+e.toString());
}
}
});
}
} catch (Exception e) {
// TODO Auto-generated catch block
System.out.println("\nresponce code error "+e.toString());
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
// TODO Auto-generated method stub
Status.show("Check your internet connection!", 2000);
}
});
}
}
}
public void drawListRow (ListField listField, Graphics graphics, int index, int y, int w) {
try {
graphics.setGlobalAlpha(255);
final int margin =5;
String tittle = (String)elements.elementAt(index);
String content = (String)contentelements.elementAt(index);
String date = (String)datelements.elementAt(index);
String imagesurl = (String)Imageselements.elementAt(index);
UrlToImage img = new UrlToImage( imagesurl);
bit =img.getbitmap();
graphics.drawText(tittle.trim(), 3*margin+bit.getWidth(), y+margin);
graphics.drawText(content.trim(), 3*margin+bit.getWidth(), y+ margin+30);
graphics.drawText(date.trim(), 3*margin+bit.getWidth(), y+ margin+60);
graphics.drawBitmap(2, y+margin+5, bit.getWidth(), bit.getHeight(), bit, 0, 0);
} catch (Exception e) {
// TODO Auto-generated catch block
System.out.println("error drawListRow"+e.toString());
}
}
public Object get(ListField listField, int index) {
// TODO Auto-generated method stub
return null;
}
public int getPreferredWidth(ListField listField) {
// TODO Auto-generated method stub
return 0;
}
public int indexOfList(ListField listField, String prefix, int start) {
// TODO Auto-generated method stub
return 0;
}
和 MY UrlToImage.java 类，它从 URL 下载图像
public class UrlToImage {
public static Bitmap _bmap;
UrlToImage(final String url){
HttpConnection connection = null;
InputStream inputStream = null;
EncodedImage bitmap;
byte[] dataArray = null;
try {
connection = (HttpConnection) Connector.open(url+ getConnectionString(), Connector.READ, true);
inputStream = connection.openInputStream();
byte[] responseData = new byte[10000];
int length = 0;
StringBuffer rawResponse = new StringBuffer();
while (-1 != (length = inputStream.read(responseData)))
{
rawResponse.append(new String(responseData, 0, length));
}
int responseCode = connection.getResponseCode();
if (responseCode != HttpConnection.HTTP_OK)
{
throw new IOException("HTTP response code: "+ responseCode);
}else{
System.out.println("\nHttpConnection.HTTP_OK = "+responseCode);
}
final String result = rawResponse.toString();
dataArray = result.getBytes();
/*System.out.println("\ndataArray.length = "+dataArray.length);
System.out.println("\ndataArray.length = "+dataArray[0]);
System.out.println("\ndataArray.length = "+dataArray[1]);
System.out.println("\ndataArray.length = "+dataArray[2]);
System.out.println("\ndataArray.length = "+dataArray[3]);*/
} catch (final Exception ex) {
}finally {
try {
inputStream.close();
inputStream = null;
connection.close();
connection = null;
}
catch(Exception e){
}
}
bitmap = EncodedImage.createEncodedImage(dataArray, 0,dataArray.length);
// this will scale your image acc. to your height and width of bitmapfield
int multH;
int multW;
int currHeight = bitmap.getHeight();
int currWidth = bitmap.getWidth();
multH= Fixed32.div(Fixed32.toFP(currHeight),Fixed32.toFP(80));//height
multW = Fixed32.div(Fixed32.toFP(currWidth),Fixed32.toFP(80));//width
bitmap = bitmap.scaleImage32(multW,multH);
_bmap=bitmap.getBitmap();
}
public String getConnectionString() {
String connectionString = null;
// Simulator behaviour is controlled by the USE_MDS_IN_SIMULATOR
// variable.
if (DeviceInfo.isSimulator()) {
connectionString = ";deviceside=true";
System.out.println("11111111111111111");
}
// Wifi is the preferred transmission method
else if (WLANInfo.getWLANState() == WLANInfo.WLAN_STATE_CONNECTED) {
connectionString = ";interface=wifi";
System.out.println("222222222222222222");
}
// Is the carrier network the only way to connect?
else if ((CoverageInfo.getCoverageStatus() & CoverageInfo.COVERAGE_DIRECT) == CoverageInfo.COVERAGE_DIRECT)
{
String carrierUid = getCarrierBIBSUid();
if (carrierUid == null) {
// Has carrier coverage, but not BIBS. So use the carrier's TCP
// network
System.out.println("33333333333333333");
connectionString = ";deviceside=true";
} else {
// otherwise, use the Uid to construct a valid carrier BIBS
// request
System.out.println("444444444444444444");
connectionString = ";deviceside=false;connectionUID="+carrierUid + ";ConnectionType=mds-public";
}
}
// Check for an MDS connection instead (BlackBerry Enterprise Server)
else if ((CoverageInfo.getCoverageStatus() & CoverageInfo.COVERAGE_MDS) == CoverageInfo.COVERAGE_MDS)
{
System.out.println("55555555555555555555");
connectionString = ";deviceside=false";
}
// If there is no connection available abort to avoid hassling the user
// unnecssarily.
else if (CoverageInfo.getCoverageStatus() == CoverageInfo.COVERAGE_NONE)
{
System.out.println("66666666666666666666");
connectionString = "none";
}
// In theory, all bases are covered by now so this shouldn't be reachable.But hey, just in case ...
else {
System.out.println("77777777777777777777777");
connectionString = ";deviceside=true";
}
return connectionString;
}
/**//**
* Looks through the phone's service book for a carrier provided BIBS
* network
*
* @return The uid used to connect to that network.
*//*
*/ private synchronized String getCarrierBIBSUid() {
ServiceRecord[] records = ServiceBook.getSB().getRecords();
int currentRecord;
for (currentRecord = 0; currentRecord < records.length; currentRecord++) {
if (records[currentRecord].getCid().toLowerCase().equals("ippp")) {
if (records[currentRecord].getName().toLowerCase()
.indexOf("bibs") >= 0) {
return records[currentRecord].getUid();
}
}
}
return null;
}
public Bitmap getbitmap()
{
return _bmap;
}
}
最佳答案
对于 ListField，此方法:
public void drawListRow (ListField listField, Graphics graphics, int index, int y, int w)
将在主(又名“UI”)线程上调用。此方法用于绘图。但是，该方法中有以下代码行:
UrlToImage img = new UrlToImage( imagesurl);
bit =img.getbitmap();
由于您已经实现了 UrlToImage 类，因此该代码正在进行网络调用。不应在 UI 线程上进行网络调用。如果这样做，您的 UI 将挂起/卡住。
您应该做的是创建一个后台工作线程(线程)，它将访问网络来获取您的图像。您可以决定是否需要在后台立即加载所有图像，或者仅在用户滚动ListField时加载图像。当图像到达(在后台线程上)时，您应该告诉列表字段逐行重绘自身。
您可能想看一下at this recent answer ，它在后台执行图像的延迟加载。这个答案有点不同，因为它使用自定义列表，而不是标准的 ListField。对于标准 ListField，您可以使用 ListField#invalidate(int) 触发列表行的重绘。 :
// image for row 'x' download complete. save image as member data
// that can be accessed in drawListRow().
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
_list.invalidate(x);
}
});
关于java - 在 json 的列表字段中显示数据和图像，就像延迟加载黑莓一样，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/19723189/