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我使用了以下链接中的代码：Signare's Blog。我有 10 个图像 URL，想检索它们并将它们显示在我的屏幕上。当我使用上述链接中的代码时，加载所有图像需要 10 多分钟。如何加快加载速度？

URLBitmapField post_img= new URLBitmapField(image_url);
add(post_img);

其中类URLBitmapField定义为：

import net.rim.device.api.math.Fixed32;
import net.rim.device.api.system.Bitmap;
import net.rim.device.api.system.EncodedImage;
import net.rim.device.api.ui.UiApplication;
import net.rim.device.api.ui.component.BitmapField;

public class URLBitmapField extends BitmapField implements URLDataCallback {
    EncodedImage result = null;
    public static EncodedImage _encoded_img = null;
    int _imgWidth = 52;
    int _imgHeight = 62;
    int _imgMargin = 10;

    public URLBitmapField(String url) {
        try {
            http_image_data_extrator.getWebData(url, this);
        }
        catch (Exception e) {}
    }

    public Bitmap getBitmap() {
        if (_encoded_img == null) return null;
        return _encoded_img.getBitmap();
    }

    public void callback(final String data) {
        if (data.startsWith("Exception")) return;
        try {
            byte[] dataArray = data.getBytes();
            _encoded_img = EncodedImage.createEncodedImage(dataArray, 0, dataArray.length); // with scale
            _encoded_img = sizeImage(_encoded_img, _imgWidth, _imgHeight);
            setImage(_encoded_img);
            UiApplication.getUiApplication().getActiveScreen().invalidate();
        }
        catch (final Exception e){}
    }

    public EncodedImage sizeImage(EncodedImage image, int width, int height) {
        int currentWidthFixed32 = Fixed32.toFP(image.getWidth());
        int currentHeightFixed32 = Fixed32.toFP(image.getHeight());
        int requiredWidthFixed32 = Fixed32.toFP(width);
        int requiredHeightFixed32 = Fixed32.toFP(height);
        int scaleXFixed32 = Fixed32.div(currentWidthFixed32,requiredWidthFixed32);
        int scaleYFixed32 = Fixed32.div(currentHeightFixed32,requiredHeightFixed32);
        result = image.scaleImage32(scaleXFixed32, scaleYFixed32);
        return result;
    }
}

public interface URLDataCallback {
    public void callback(String data);
}

该类http_image_data_extrator定义为：

import java.io.IOException;
import java.io.InputStream;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import net.rim.device.api.system.RadioInfo;
import net.rim.device.api.system.WLANInfo;
import net.rim.device.api.ui.UiApplication;

public class http_image_data_extrator {
    static String url_="";
    static StringBuffer rawResponse=null;

    public static void getWebData(String url, final URLDataCallback callback) throws IOException {
        HttpConnection connection = null;
        InputStream inputStream = null;
        try {
            if ((WLANInfo.getWLANState() == WLANInfo.WLAN_STATE_CONNECTED)&& RadioInfo.areWAFsSupported(RadioInfo.WAF_WLAN)) {
                url += ";interface=wifi";
            }
            connection = (HttpConnection) Connector.open(url, Connector.READ, true);
            String location=connection.getHeaderField("location");
            if(location!=null){
                if ((WLANInfo.getWLANState() == WLANInfo.WLAN_STATE_CONNECTED)&& RadioInfo.areWAFsSupported(RadioInfo.WAF_WLAN)) {
                    location += ";interface=wifi";
                }
                connection = (HttpConnection) Connector.open(location, Connector.READ, true);
            }else{
                connection = (HttpConnection) Connector.open(url, Connector.READ, true);
            }

            inputStream = connection.openInputStream();
            byte[] responseData = new byte[10000];
            int length = 0;
            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);
            }

            final String  result = rawResponse.toString();
            UiApplication.getUiApplication().invokeLater(new Runnable() {
                public void run(){
                    callback.callback(result);
                }
            });
        }
        catch (final Exception ex) {
            UiApplication.getUiApplication().invokeLater(new Runnable() {
                public void run() {
                    callback.callback("Exception (" + ex.getClass() + "): " + ex.getMessage());
                }
            });
        }
    }
}
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1 回答 1

1

在服务器上调整大小

调整服务器上的图像大小是最好的答案。因为下载大图像并缩小它们需要设备上的很多东西（网络、内存、cpu）。

通过代理调整大小

如果图像服务器不在您的控制之下，您仍然可以使用自己的服务器作为调整大小的代理（将图像 url 和所需大小发送到您的服务器，它会获取图像、调整大小并返回调整大小的图像）。也许已经有一项服务可以做到这一点。

更便宜的解码选项

一些解码选项可能会使解码（和调整大小）更便宜。DECODE_NO_DITHER、DECODE_READONLY 和 DECODE_NATIVE 似乎都值得一试。
http://www.blackberry.com/developers/docs/4.2api/net/rim/device/api/system/EncodedImage.html#DECODE_NO_DITHER

串行而不是并行

您提到您正在加载 10 张图像。如果 10 张图像所用时间是 1 张图像所用时间的 10 倍以上，则系统可能会“抖动”。就像它可能会启动所有 10 个请求，然后在回调中同时处理内存中的 10 个全尺寸图像。可以尝试在开始下载下一张之前显示第一张图片，这也让用户可以更快地查看。同样，并行调用 invalidate 10 次（在回调中）可能会导致打嗝。

于 2013-02-24T20:15:57.147 回答