Question

如何在自定义ListView中加载动态图像iI按照本教程在水平http://www.dev-smart.com/archives/34中显示ListView，但问题是此示例使用了相同的示例图标，但我想使用动态图像来自资源或网络解析

HorizontalListViewDemo.java：

public class HorizontalListViewDemo extends Activity {  

    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  

        setContentView(R.layout.listviewdemo);  

        HorizontialListView listview = (HorizontialListView) findViewById(R.id.listview);  
        listview.setAdapter(mAdapter);  
    }  

    private static String[] dataObjects = new String[]{ "Text #1",  
        "Text #2",  
        "Text #3" };   

    private BaseAdapter mAdapter = new BaseAdapter() {  

        @Override  
        public int getCount() {  
            return dataObjects.length;  
        }  

        @Override  
        public Object getItem(int position) {  
            return null;  
        }

        @Override  
        public long getItemId(int position) {
            return 0;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {  
            View retval =  
                LayoutInflater.from(parent.getContext()).inflate(R.layout.viewitem, null);  
            TextView title = (TextView) retval.findViewById(R.id.title);  
            title.setText(dataObjects[position]);  

            return retval;
        }

    };

}

布局文件：

   <linearlayout xmlns:android="http://schemas.android.com/apk/res 
   /android" android:orientation="vertical"
      android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="#fff">  

    <com.devsmart.android.ui.horizontiallistview android:id="@+id/listview"      
        android:layout_width="fill_parent"
    android:layout_height="wrap_content" 
           android:background="#ddd">  

        </com.devsmart.android.ui.horizontiallistview>
          </linearlayout> 

       <linearlayout xmlns:android="http://schemas.android.com 
      /apk/res/android" android:orientation="vertical"      
      android:layout_width="wrap_content"
      android:layout_height="wrap_content" android:background="#fff">  

    <imageview android:id="@+id/image" 
     android:layout_width="150dip"
    android:layout_height="150dip"
    android:scaletype="centerCrop" 
    android:src="@drawable/icon">  

    <textview android:id="@+id/title"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
     android:textcolor="#000"
        android:gravity="center_horizontal">  

    </textview></imageview></linearlayout>

HorizontalListView.java

 public class HorizontalListView extends  
               AdapterView<ListAdapter> {

public boolean mAlwaysOverrideTouch = true;
protected ListAdapter mAdapter;
private int mLeftViewIndex = -1;
private int mRightViewIndex = 0;
protected int mCurrentX;
protected int mNextX;
private int mMaxX = Integer.MAX_VALUE;
private int mDisplayOffset = 0;
protected Scroller mScroller;
private GestureDetector mGesture;
private Queue<View> mRemovedViewQueue = new LinkedList<View>();
private OnItemSelectedListener mOnItemSelected;
private OnItemClickListener mOnItemClicked;
private OnItemLongClickListener mOnItemLongClicked;
private boolean mDataChanged = false;


public HorizontalListView(Context context, AttributeSet attrs) {
    super(context, attrs);
    initView();
}

private synchronized void initView() {
    mLeftViewIndex = -1;
    mRightViewIndex = 0;
    mDisplayOffset = 0;
    mCurrentX = 0;
    mNextX = 0;
    mMaxX = Integer.MAX_VALUE;
    mScroller = new Scroller(getContext());
    mGesture = new GestureDetector(getContext(), mOnGesture);
}

@Override
public void setOnItemSelectedListener(AdapterView.OnItemSelectedListener 

        listener)  {
    mOnItemSelected = listener;
}

@Override
public void setOnItemClickListener(AdapterView.OnItemClickListener listener){
    mOnItemClicked = listener;
}

@Override
public void setOnItemLongClickListener(AdapterView.OnItemLongClickListener 
      listener) {
    mOnItemLongClicked = listener;
}

private DataSetObserver mDataObserver = new DataSetObserver() {

    @Override
    public void onChanged() {
        synchronized(HorizontalListView.this){
            mDataChanged = true;
        }
        invalidate();
        requestLayout();
    }

    @Override
    public void onInvalidated() {
        reset();
        invalidate();
        requestLayout();
    }

};

@Override
public ListAdapter getAdapter() {
    return mAdapter;
}

@Override
public View getSelectedView() {
    //TODO: implement
    return null;
}

@Override
public void setAdapter(ListAdapter adapter) {
    if(mAdapter != null) {
        mAdapter.unregisterDataSetObserver(mDataObserver);
    }
    mAdapter = adapter;
    mAdapter.registerDataSetObserver(mDataObserver);
    reset();
}

private synchronized void reset(){
    initView();
    removeAllViewsInLayout();
    requestLayout();
}

@Override
public void setSelection(int position) {
    //TODO: implement
}

private void addAndMeasureChild(final View child, int viewPos) {
    LayoutParams params = child.getLayoutParams();
    if(params == null) {
        params = new LayoutParams(LayoutParams.FILL_PARENT, 
        LayoutParams.FILL_PARENT);
    }

    addViewInLayout(child, viewPos, params, true);
    child.measure(MeasureSpec.makeMeasureSpec(getWidth(), MeasureSpec.AT_MOST),
            MeasureSpec.makeMeasureSpec(getHeight(), 
        MeasureSpec.AT_MOST));
}



@Override
protected synchronized void onLayout(boolean changed, int left, int top, int 
    right, int bottom) {
    super.onLayout(changed, left, top, right, bottom);

    if(mAdapter == null){
        return;
    }

    if(mDataChanged){
        int oldCurrentX = mCurrentX;
        initView();
        removeAllViewsInLayout();
        mNextX = oldCurrentX;
        mDataChanged = false;
    }

    if(mScroller.computeScrollOffset()){
        int scrollx = mScroller.getCurrX();
        mNextX = scrollx;
    }

    if(mNextX <= 0){
        mNextX = 0;
        mScroller.forceFinished(true);
    }
    if(mNextX >= mMaxX) {
        mNextX = mMaxX;
        mScroller.forceFinished(true);
    }

    int dx = mCurrentX - mNextX;

    removeNonVisibleItems(dx);
    fillList(dx);
    positionItems(dx);

    mCurrentX = mNextX;

    if(!mScroller.isFinished()){
        post(new Runnable(){
            @Override
            public void run() {
                requestLayout();
            }
        });

    }
}

private void fillList(final int dx) {
    int edge = 0;
    View child = getChildAt(getChildCount()-1);
    if(child != null) {
        edge = child.getRight();
    }
    fillListRight(edge, dx);

    edge = 0;
    child = getChildAt(0);
    if(child != null) {
        edge = child.getLeft();
    }
    fillListLeft(edge, dx);


}

 private void fillListRight(int rightEdge, final int dx) {
    while(rightEdge + dx < getWidth() && mRightViewIndex < 
         mAdapter.getCount()) {

        View child = mAdapter.getView(mRightViewIndex, 
            mRemovedViewQueue.poll(), this);
        addAndMeasureChild(child, -1);
        rightEdge += child.getMeasuredWidth();

        if(mRightViewIndex == mAdapter.getCount()-1) {
            mMaxX = mCurrentX + rightEdge - getWidth();
        }

        if (mMaxX < 0) {
            mMaxX = 0;
        }
        mRightViewIndex++;
    }

}

 private void fillListLeft(int leftEdge, final int dx) {
    while(leftEdge + dx > 0 && mLeftViewIndex >= 0) {
        View child = mAdapter.getView(mLeftViewIndex, 
             mRemovedViewQueue.poll(), this);
        addAndMeasureChild(child, 0);
        leftEdge -= child.getMeasuredWidth();
        mLeftViewIndex--;
        mDisplayOffset -= child.getMeasuredWidth();
    }
}

private void removeNonVisibleItems(final int dx) {
    View child = getChildAt(0);
    while(child != null && child.getRight() + dx <= 0) {
        mDisplayOffset += child.getMeasuredWidth();
        mRemovedViewQueue.offer(child);
        removeViewInLayout(child);
        mLeftViewIndex++;
        child = getChildAt(0);

    }

    child = getChildAt(getChildCount()-1);
    while(child != null && child.getLeft() + dx >= getWidth()) {
        mRemovedViewQueue.offer(child);
        removeViewInLayout(child);
        mRightViewIndex--;
        child = getChildAt(getChildCount()-1);
    }
}

private void positionItems(final int dx) {
    if(getChildCount() > 0){
        mDisplayOffset += dx;
        int left = mDisplayOffset;
        for(int i=0;i<getChildCount();i++){
            View child = getChildAt(i);
            int childWidth = child.getMeasuredWidth();
            child.layout(left, 0, left + childWidth, 
         child.getMeasuredHeight());
            left += childWidth + child.getPaddingRight();
        }
    }
}

public synchronized void scrollTo(int x) {
    mScroller.startScroll(mNextX, 0, x - mNextX, 0);
    requestLayout();
}

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
    boolean handled = super.dispatchTouchEvent(ev);
    handled |= mGesture.onTouchEvent(ev);
    return handled;
}

protected boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
            float velocityY) {
    synchronized(HorizontalListView.this){
        mScroller.fling(mNextX, 0, (int)-velocityX, 0, 0, mMaxX, 0, 0);
    }
    requestLayout();

    return true;
}

protected boolean onDown(MotionEvent e) {
    mScroller.forceFinished(true);
    return true;
}

private OnGestureListener mOnGesture = new 
         GestureDetector.SimpleOnGestureListener() {

    @Override
    public boolean onDown(MotionEvent e) {
        return HorizontalListView.this.onDown(e);
    }

    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
            float velocityY) {
        return HorizontalListView.this.onFling(e1, e2, velocityX, 
           velocityY);
    }

    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2,
            float distanceX, float distanceY) {

        synchronized(HorizontalListView.this){
            mNextX += (int)distanceX;
        }
        requestLayout();

        return true;
     }

    @Override
    public boolean onSingleTapConfirmed(MotionEvent e) {
        for(int i=0;i<getChildCount();i++){
            View child = getChildAt(i);
            if (isEventWithinView(e, child)) {
                if(mOnItemClicked != null){

      mOnItemClicked.onItemClick(HorizontalListView.this, child, mLeftViewIndex + 1 +  
        i, mAdapter.getItemId( mLeftViewIndex + 1 + i ));
                }
                if(mOnItemSelected != null){

     mOnItemSelected.onItemSelected(HorizontalListView.this, child, mLeftViewIndex + 
    1  + i, mAdapter.getItemId( mLeftViewIndex + 1 + i ));
                }
                break;
            }

        }
        return true;
    }

    @Override
    public void onLongPress(MotionEvent e) {
        int childCount = getChildCount();
        for (int i = 0; i < childCount; i++) {
            View child = getChildAt(i);
            if (isEventWithinView(e, child)) {
                if (mOnItemLongClicked != null) {

  mOnItemLongClicked.onItemLongClick(HorizontalListView.this, child, mLeftViewIndex + 
    1 + i, mAdapter.getItemId(mLeftViewIndex + 1 + i));
                }
                break;
            }

        }
    }

    private boolean isEventWithinView(MotionEvent e, View child) {
        Rect viewRect = new Rect();
        int[] childPosition = new int[2];
        child.getLocationOnScreen(childPosition);
        int left = childPosition[0];
        int right = left + child.getWidth();
        int top = childPosition[1];
        int bottom = top + child.getHeight();
        viewRect.set(left, top, right, bottom);
        return viewRect.contains((int) e.getRawX(), (int) e.getRawY());
    }
};

}

Answer 1

请看下面的链接。有人已经为它编写了一个库。

Android Universal Image Loader

我在最近的项目中使用了this库，它运行得很完美。

希望它会有所帮助。

Answer 2

以下是您正在寻找的内容..

Answer 3

正如@Varundroid所说，你可以使用Android通用图像加载器，它的工作效果非常好。但对于这么小的目的来说，这是一个巨大的图书馆。您可以考虑编写自己的Asynchronous Image Loader for Android ListView

您可以在适配器类中更改以下内容

public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;
        if (convertView == null) {
            convertView = layoutInflater.inflate(R.layout.list_row_layout, null);
            holder = new ViewHolder();            
            holder.imageView = (ImageView) convertView.findViewById(R.id.thumbImage);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        NewsItem newsItem = (NewsItem) listData.get(position); 
        if (holder.imageView != null) {
            new ImageDownloaderTask(holder.imageView).execute(newsItem.getUrl());
        } 
        return convertView;
    }

用于在单独的线程中下载图像

class ImageDownloaderTask extends AsyncTask<String, Void, Bitmap> {
    private final WeakReference imageViewReference;

    public ImageDownloaderTask(ImageView imageView) {
        imageViewReference = new WeakReference(imageView);
    }

    @Override
    // Actual download method, run in the task thread
    protected Bitmap doInBackground(String... params) {
        // params comes from the execute() call: params[0] is the url.
        return downloadBitmap(params[0]);
    }

    @Override
    // Once the image is downloaded, associates it to the imageView
    protected void onPostExecute(Bitmap bitmap) {
        if (isCancelled()) {
            bitmap = null;
        }

        if (imageViewReference != null) {
            ImageView imageView = imageViewReference.get();
            if (imageView != null) {

                if (bitmap != null) {
                    imageView.setImageBitmap(bitmap);
                } else {
                    imageView.setImageDrawable(imageView.getContext().getResources()
                            .getDrawable(R.drawable.list_placeholder));
                }
            }

        }
    }

}

上面的链接有完整的教程供您使用。

如何在自定义ListView中加载动态图像

3 个答案: