/**
* 源码片段
* 自定义的ScrollView，在其中动态地对图片进行添加。
*
* @author guolin
*/
public class MyScrollView extends ScrollView implements OnTouchListener {
/**
* 每页要加载的图片数量
*/
public static final int PAGE_SIZE = 15;
/**
* 记录当前已加载到第几页
*/
private int page;
/**
* 每一列的宽度
*/
private int columnWidth;
/**
* 当前第一列的高度
*/
private int firstColumnHeight;
/**
* 当前第二列的高度
*/
private int secondColumnHeight;
/**
* 当前第三列的高度
*/
private int thirdColumnHeight;
/**
* 是否已加载过一次layout，这里onLayout中的初始化只需加载一次
*/
private boolean loadOnce;
/**
* 对图片进行管理的工具类
*/
private ImageLoader p_w_picpathLoader;
/**
* 第一列的布局
*/
private LinearLayout firstColumn;
/**
* 第二列的布局
*/
private LinearLayout secondColumn;
/**
* 第三列的布局
*/
private LinearLayout thirdColumn;
/**
* 记录所有正在下载或等待下载的任务。
*/
private static Set<loadp_w_picpathtask> taskCollection;
/**
* MyScrollView下的直接子布局。
*/
private static View scrollLayout;
/**
* MyScrollView布局的高度。
*/
private static int scrollViewHeight;
/**
* 记录上垂直方向的滚动距离。
*/
private static int lastScrollY = -1;
/**
* 记录所有界面上的图片，用以可以随时控制对图片的释放。
*/
private List<p_w_picpathview> p_w_picpathViewList = new ArrayList<p_w_picpathview>();
/**
* 在Handler中进行图片可见性检查的判断，以及加载更多图片的操作。
*/
private static Handler handler = new Handler() {
public void handleMessage(android.os.Message msg) {
MyScrollView myScrollView = (MyScrollView) msg.obj;
int scrollY = myScrollView.getScrollY();
// 如果当前的滚动位置和上次相同，表示已停止滚动
if (scrollY == lastScrollY) {
// 当滚动的最底部，并且当前没有正在下载的任务时，开始加载下一页的图片
if (scrollViewHeight + scrollY >= scrollLayout.getHeight()
&& taskCollection.isEmpty()) {
myScrollView.loadMoreImages();
}
myScrollView.checkVisibility();
} else {
lastScrollY = scrollY;
Message message = new Message();
message.obj = myScrollView;
// 5毫秒后再次对滚动位置进行判断
handler.sendMessageDelayed(message, 5);
}
};
};
/**
* MyScrollView的构造函数。
*
* @param context
* @param attrs
*/
public MyScrollView(Context context, AttributeSet attrs) {
super(context, attrs);
p_w_picpathLoader = ImageLoader.getInstance();
taskCollection = new HashSet<loadp_w_picpathtask>();
setOnTouchListener(this);
}
/**
* 进行一些关键性的初始化操作，获取MyScrollView的高度，以及得到第一列的宽度值。并在这里开始加载第一页的图片。
*/
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
if (changed && !loadOnce) {
scrollViewHeight = getHeight();
scrollLayout = getChildAt(0);
firstColumn = (LinearLayout) findViewById(R.id.first_column);
secondColumn = (LinearLayout) findViewById(R.id.second_column);
thirdColumn = (LinearLayout) findViewById(R.id.third_column);
columnWidth = firstColumn.getWidth();
loadOnce = true;
loadMoreImages();
}
}
/**
* 监听用户的触屏事件，如果用户手指离开屏幕则开始进行滚动检测。
*/
@Override
public boolean onTouch(View v, MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_UP) {
Message message = new Message();
message.obj = this;
handler.sendMessageDelayed(message, 5);
}
return false;
}
/**
* 开始加载下一页的图片，每张图片都会开启一个异步线程去下载。
*/
public void loadMoreImages() {
if (hasSDCard()) {
int startIndex = page * PAGE_SIZE;
int endIndex = page * PAGE_SIZE + PAGE_SIZE;
if (startIndex < Images.p_w_picpathUrls.length) {
Toast.makeText(getContext(), "正在加载...", Toast.LENGTH_SHORT)
.show();
if (endIndex > Images.p_w_picpathUrls.length) {
endIndex = Images.p_w_picpathUrls.length;
}
for (int i = startIndex; i < endIndex; i++) {
LoadImageTask task = new LoadImageTask();
taskCollection.add(task);
task.execute(Images.p_w_picpathUrls[i]);
}
page++;
} else {
Toast.makeText(getContext(), "已没有更多图片", Toast.LENGTH_SHORT)
.show();
}
} else {
Toast.makeText(getContext(), "未发现SD卡", Toast.LENGTH_SHORT).show();
}
}
/**
* 遍历p_w_picpathViewList中的每张图片，对图片的可见性进行检查，如果图片已经离开屏幕可见范围，则将图片替换成一张空图。
*/
public void checkVisibility() {
for (int i = 0; i < p_w_picpathViewList.size(); i++) {
ImageView p_w_picpathView = p_w_picpathViewList.get(i);
int borderTop = (Integer) p_w_picpathView.getTag(R.string.border_top);
int borderBottom = (Integer) p_w_picpathView
.getTag(R.string.border_bottom);
if (borderBottom > getScrollY()
&& borderTop < getScrollY() + scrollViewHeight) {
String p_w_picpathUrl = (String) p_w_picpathView.getTag(R.string.p_w_picpath_url);
Bitmap bitmap = p_w_picpathLoader.getBitmapFromMemoryCache(p_w_picpathUrl);
if (bitmap != null) {
p_w_picpathView.setImageBitmap(bitmap);
} else {
LoadImageTask task = new LoadImageTask(p_w_picpathView);
task.execute(p_w_picpathUrl);
}
} else {
p_w_picpathView.setImageResource(R.drawable.empty_photo);
}
}
}
/**
* 判断手机是否有SD卡。
*
* @return 有SD卡返回true，没有返回false。
*/
private boolean hasSDCard() {
return Environment.MEDIA_MOUNTED.equals(Environment
.getExternalStorageState());
}
/**
* 异步下载图片的任务。
*
* @author guolin
*/
class LoadImageTask extends AsyncTask<string, void,="" bitmap=""> {
/**
* 图片的URL地址
*/
private String mImageUrl;
/**
* 可重复使用的ImageView
*/
private ImageView mImageView;
public LoadImageTask() {
}
/**
* 将可重复使用的ImageView传入
*
* @param p_w_picpathView
*/
public LoadImageTask(ImageView p_w_picpathView) {
mImageView = p_w_picpathView;
}
@Override
protected Bitmap doInBackground(String... params) {
mImageUrl = params[0];
Bitmap p_w_picpathBitmap = p_w_picpathLoader
.getBitmapFromMemoryCache(mImageUrl);
if (p_w_picpathBitmap == null) {
p_w_picpathBitmap = loadImage(mImageUrl);
}
return p_w_picpathBitmap;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
if (bitmap != null) {
double ratio = bitmap.getWidth() / (columnWidth * 1.0);
int scaledHeight = (int) (bitmap.getHeight() / ratio);
addImage(bitmap, columnWidth, scaledHeight);
}
taskCollection.remove(this);
}
/**
* 根据传入的URL，对图片进行加载。如果这张图片已经存在于SD卡中，则直接从SD卡里读取，否则就从网络上下载。
*
* @param p_w_picpathUrl
* 图片的URL地址
* @return 加载到内存的图片。
*/
private Bitmap loadImage(String p_w_picpathUrl) {
File p_w_picpathFile = new File(getImagePath(p_w_picpathUrl));
if (!p_w_picpathFile.exists()) {
downloadImage(p_w_picpathUrl);
}
if (p_w_picpathUrl != null) {
Bitmap bitmap = ImageLoader.decodeSampledBitmapFromResource(
p_w_picpathFile.getPath(), columnWidth);
if (bitmap != null) {
p_w_picpathLoader.addBitmapToMemoryCache(p_w_picpathUrl, bitmap);
return bitmap;
}
}
return null;
}
/**
* 向ImageView中添加一张图片
*
* @param bitmap
* 待添加的图片
* @param p_w_picpathWidth
* 图片的宽度
* @param p_w_picpathHeight
* 图片的高度
*/
private void addImage(Bitmap bitmap, int p_w_picpathWidth, int p_w_picpathHeight) {
LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
p_w_picpathWidth, p_w_picpathHeight);
if (mImageView != null) {
mImageView.setImageBitmap(bitmap);
} else {
ImageView p_w_picpathView = new ImageView(getContext());
p_w_picpathView.setLayoutParams(params);
p_w_picpathView.setImageBitmap(bitmap);
p_w_picpathView.setScaleType(ScaleType.FIT_XY);
p_w_picpathView.setPadding(5, 5, 5, 5);
p_w_picpathView.setTag(R.string.p_w_picpath_url, mImageUrl);
findColumnToAdd(p_w_picpathView, p_w_picpathHeight).addView(p_w_picpathView);
p_w_picpathViewList.add(p_w_picpathView);
}
}
/**
* 找到此时应该添加图片的一列。原则就是对三列的高度进行判断，当前高度最小的一列就是应该添加的一列。
*
* @param p_w_picpathView
* @param p_w_picpathHeight
* @return 应该添加图片的一列
*/
private LinearLayout findColumnToAdd(ImageView p_w_picpathView,
int p_w_picpathHeight) {
if (firstColumnHeight <= secondColumnHeight) {
if (firstColumnHeight <= thirdColumnHeight) {
p_w_picpathView.setTag(R.string.border_top, firstColumnHeight);
firstColumnHeight += p_w_picpathHeight;
p_w_picpathView.setTag(R.string.border_bottom, firstColumnHeight);
return firstColumn;
}
p_w_picpathView.setTag(R.string.border_top, thirdColumnHeight);
thirdColumnHeight += p_w_picpathHeight;
p_w_picpathView.setTag(R.string.border_bottom, thirdColumnHeight);
return thirdColumn;
} else {
if (secondColumnHeight <= thirdColumnHeight) {
p_w_picpathView.setTag(R.string.border_top, secondColumnHeight);
secondColumnHeight += p_w_picpathHeight;
p_w_picpathView
.setTag(R.string.border_bottom, secondColumnHeight);
return secondColumn;
}
p_w_picpathView.setTag(R.string.border_top, thirdColumnHeight);
thirdColumnHeight += p_w_picpathHeight;
p_w_picpathView.setTag(R.string.border_bottom, thirdColumnHeight);
return thirdColumn;
}
}
/**
* 将图片下载到SD卡缓存起来。
*
* @param p_w_picpathUrl
* 图片的URL地址。
*/
private void downloadImage(String p_w_picpathUrl) {
if (Environment.getExternalStorageState().equals(
Environment.MEDIA_MOUNTED)) {
Log.d("TAG", "monted sdcard");
} else {
Log.d("TAG", "has no sdcard");
}
HttpURLConnection con = null;
FileOutputStream fos = null;
BufferedOutputStream bos = null;
BufferedInputStream bis = null;
File p_w_picpathFile = null;
try {
URL url = new URL(p_w_picpathUrl);
con = (HttpURLConnection) url.openConnection();
con.setConnectTimeout(5 * 1000);
con.setReadTimeout(15 * 1000);
con.setDoInput(true);
con.setDoOutput(true);
bis = new BufferedInputStream(con.getInputStream());
p_w_picpathFile = new File(getImagePath(p_w_picpathUrl));
fos = new FileOutputStream(p_w_picpathFile);
bos = new BufferedOutputStream(fos);
byte[] b = new byte[1024];
int length;
while ((length = bis.read(b)) != -1) {
bos.write(b, 0, length);
bos.flush();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if (bis != null) {
bis.close();
}
if (bos != null) {
bos.close();
}
if (con != null) {
con.disconnect();
}
} catch (IOException e) {
e.printStackTrace();
}
}
if (p_w_picpathFile != null) {
Bitmap bitmap = ImageLoader.decodeSampledBitmapFromResource(
p_w_picpathFile.getPath(), columnWidth);
if (bitmap != null) {
p_w_picpathLoader.addBitmapToMemoryCache(p_w_picpathUrl, bitmap);
}
}
}
/**
* 获取图片的本地存储路径。
*
* @param p_w_picpathUrl
* 图片的URL地址。
* @return 图片的本地存储路径。
*/
private String getImagePath(String p_w_picpathUrl) {
int lastSlashIndex = p_w_picpathUrl.lastIndexOf("/");
String p_w_picpathName = p_w_picpathUrl.substring(lastSlashIndex + 1);
String p_w_picpathDir = Environment.getExternalStorageDirectory()
.getPath() + "/PhotoWallFalls/";
File file = new File(p_w_picpathDir);
if (!file.exists()) {
file.mkdirs();
}
String p_w_picpathPath = p_w_picpathDir + p_w_picpathName;
return p_w_picpathPath;
}
}
}</string,></loadp_w_picpathtask></p_w_picpathview></p_w_picpathview></loadp_w_picpathtask>
转载于:https://blog.51cto.com/tongfu1013/1678259
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