Question

我正在我的Android应用程序中实现进度条。在我的应用程序中，我希望在加载所有图像后从Web上加载图像时显示进度条，应该停止加载程序。

我看到了一些进度条示例，它显示了预定义的时间段。但我希望动态进度条显示取决于从网络加载图像的时间。

Answer 1

你应该使用AsyncTask。它的Javadoc有一个你想要做的例子：

private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
     protected Long doInBackground(URL... urls) {
         int count = urls.length;
         long totalSize = 0;
         for (int i = 0; i < count; i++) {
             totalSize += Downloader.downloadFile(urls[i]);
             publishProgress((int) ((i / (float) count) * 100));
         }
         return totalSize;
     }

     protected void onProgressUpdate(Integer... progress) {
         setProgressPercent(progress[0]);
     }

     protected void onPostExecute(Long result) {
         showDialog("Downloaded " + result + " bytes");
     }
 }

您只需实施setProgressPercent方法即可在进度条中设置进度，并将其隐藏在onPostExecute上。

Answer 2

通常，您会在ASyncTask中进行下载。覆盖onPreExecute（）将允许您在后台线程启动和下载开始之前显示进度条。在AsyncTask的onPostExecute方法中，您可以隐藏进度条。

Answer 3

您还可以为每个图像添加一个加载视图，然后用户仍然可以在加载的图像中滚动，而不是仅在加载所有图像之后滚动对话框。

http://www.anddev.org/novice-tutorials-f8/imageview-with-loading-spinner-t49439.html

将此课程添加到您的项目中：

import java.io.IOException;
import java.net.MalformedURLException;

import android.content.Context;
import android.graphics.drawable.Drawable;
import android.os.Handler;
import android.os.Message;
import android.os.Handler.Callback;
import android.util.AttributeSet;
import android.view.View;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.ProgressBar;

/**
 * Free for anyone to use, just say thanks and share :-)
 * @author Blundell
 *
 */
public class LoaderImageView extends LinearLayout{

    private static final int COMPLETE = 0;
    private static final int FAILED = 1;

    private Context mContext;
    private Drawable mDrawable;
    private ProgressBar mSpinner;
    private ImageView mImage;

    /**
     * This is used when creating the view in XML
     * To have an image load in XML use the tag 'image="http://developer.android.com/images/dialog_buttons.png"'
     * Replacing the url with your desired image
     * Once you have instantiated the XML view you can call
     * setImageDrawable(url) to change the image
     * @param context
     * @param attrSet
     */
    public LoaderImageView(final Context context, final AttributeSet attrSet) {
            super(context, attrSet);
            final String url = attrSet.getAttributeValue(null, "image");
            if(url != null){
                    instantiate(context, url);
            } else {
                    instantiate(context, null);
            }
    }

    /**
     * This is used when creating the view programatically
     * Once you have instantiated the view you can call
     * setImageDrawable(url) to change the image
     * @param context the Activity context
     * @param imageUrl the Image URL you wish to load
     */
    public LoaderImageView(final Context context, final String imageUrl) {
            super(context);
            instantiate(context, imageUrl);        
    }

    /**
     *  First time loading of the LoaderImageView
     *  Sets up the LayoutParams of the view, you can change these to
     *  get the required effects you want
     */
    private void instantiate(final Context context, final String imageUrl) {
            mContext = context;

            mImage = new ImageView(mContext);
            mImage.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));

            mSpinner = new ProgressBar(mContext);
            mSpinner.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));

            mSpinner.setIndeterminate(true);

            addView(mSpinner);
            addView(mImage);

            if(imageUrl != null){
                    setImageDrawable(imageUrl);
            }
    }

    /**
     * Set's the view's drawable, this uses the internet to retrieve the image
     * don't forget to add the correct permissions to your manifest
     * @param imageUrl the url of the image you wish to load
     */
    public void setImageDrawable(final String imageUrl) {
            mDrawable = null;
            mSpinner.setVisibility(View.VISIBLE);
            mImage.setVisibility(View.GONE);
            new Thread(){
                    public void run() {
                            try {
                                    mDrawable = getDrawableFromUrl(imageUrl);
                                    imageLoadedHandler.sendEmptyMessage(COMPLETE);
                            } catch (MalformedURLException e) {
                                    imageLoadedHandler.sendEmptyMessage(FAILED);
                            } catch (IOException e) {
                                    imageLoadedHandler.sendEmptyMessage(FAILED);
                            }
                    };
            }.start();
    }

    /**
     * Callback that is received once the image has been downloaded
     */
    private final Handler imageLoadedHandler = new Handler(new Callback() {
            @Override
            public boolean handleMessage(Message msg) {
                    switch (msg.what) {
                    case COMPLETE:
                            mImage.setImageDrawable(mDrawable);
                            mImage.setVisibility(View.VISIBLE);
                            mSpinner.setVisibility(View.GONE);
                            break;
                    case FAILED:
                    default:
                            // Could change image here to a 'failed' image
                            // otherwise will just keep on spinning
                            break;
                    }
                    return true;
            }              
    });

    /**
     * Pass in an image url to get a drawable object
     * @return a drawable object
     * @throws IOException
     * @throws MalformedURLException
     */
    private static Drawable getDrawableFromUrl(final String url) throws IOException, MalformedURLException {
            return Drawable.createFromStream(((java.io.InputStream)new java.net.URL(url).getContent()), "name");
    }

}

然后可以使用以下图像加载:(将包名更改为包）

<com.blundell.tut.LoaderImageView
 android:id="@+id/loaderImageView"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 image="http://developer.android.com/images/dialog_buttons.png"
 />

或者来自代码：

final LoaderImageView image = new LoaderImageView(this, "http://developer.android.com/images/dialog_buttons.png");
    image.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));

如何显示Progressbar从Web上加载数据？

3 个答案: