How to refresh a GridView?

问题:

I have a GridView which is pretty similar to the Google tutorial, except that I want to add the ImageViews on runtime (via a subactivity). The results are okay, but the layout of the View is messed up: The GridView doesn't fill the content of its parent, what do I have to do to design it properly?

Here the code of adding the children:

public void initializeWorkbench(GridView gv, Vector<String> items) {
        Prototype.workbench.setDimension(screenWidth, divider.height()+workbenchArea.height());
        Prototype.workbench.activateWorkbench();
        // this measures the workbench correctly
        Log.d(Prototype.TAG, "workbench width: "+Prototype.workbench.getMeasuredWidth());
        // 320
        Log.d(Prototype.TAG, "workbench height: "+Prototype.workbench.getMeasuredHeight());
        // 30
        ImageAdapter imgAdapter = new ImageAdapter(this.getContext(), items);
        gv.setAdapter(imgAdapter);
        gv.measure(screenWidth, screenHeight);
        gv.requestLayout();
        gv.forceLayout();
        Log.d(Prototype.TAG, "gv width: "+gv.getMeasuredWidth());
        // 22
        Log.d(Prototype.TAG, "gv height: "+gv.getMeasuredHeight());
        // 119
        Prototype.workbench.setDimension(screenWidth, divider.height()+workbenchArea.height());
    }
}

activateWorkbench, setDimension and measure in the workbench (LinearLayout above the GridView):

public void activateWorkbench() {
    if(this.equals(Prototype.workbench)) {
        this.setOrientation(VERTICAL);
        show = true;
        measure();
    }
}

public void setDimension(int w, int h) {
    width = w;
    height = h;
    this.setLayoutParams(new LinearLayout.LayoutParams(width, height));
    this.invalidate();
}

private void measure() {
    if (this.getOrientation() == LinearLayout.VERTICAL) {
        int h = 0;
        int w = 0;
        this.measureChildren(0, 0);
        for (int i = 0; i < this.getChildCount(); i++) {
            View v = this.getChildAt(i);
            h += v.getMeasuredHeight();
            w = (w < v.getMeasuredWidth()) ? v.getMeasuredWidth() : w;
        }
        if (this.equals(Prototype.tagarea))
            height = (h < height) ? height : h;
        if (this.equals(Prototype.tagarea))
            width = (w < width) ? width : w;
    }
    this.setMeasuredDimension(width, height);
}

The ImageAdapter constructor:

public ImageAdapter(Context c, Vector<String> items) {
    mContext = c;

    boolean mExternalStorageAvailable = false;
    boolean mExternalStorageWriteable = false;
    String state = Environment.getExternalStorageState();

    if (Environment.MEDIA_MOUNTED.equals(state)) {
        // We can read and write the media
        mExternalStorageAvailable = mExternalStorageWriteable = true;
    } else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
        // We can only read the media
        mExternalStorageAvailable = true;
        mExternalStorageWriteable = false;
    } else {
        // Something else is wrong. It may be one of many other states, but
        // all we need
        // to know is we can neither read nor write
        mExternalStorageAvailable = mExternalStorageWriteable = false;
    }

    if (mExternalStorageAvailable && mExternalStorageWriteable) {
        for (String item : items) {
            File f = new File(item);
            if (f.exists()) {
                try {
                    FileInputStream fis = new FileInputStream(f);
                    Bitmap b = BitmapFactory.decodeStream(fis);
                    bitmaps.add(b);
                    files.add(f);
                } catch (FileNotFoundException e) {
                    Log.e(Prototype.TAG, "", e);
                }
            }
        }
    }
}

And the xml layout:

<LinearLayout   xmlns:android="http://schemas.android.com/apk/res/android" 
            android:layout_width="fill_parent" 
            android:layout_height="fill_parent"
                android:orientation="vertical"
                android:gravity="bottom"

                android:paddingLeft="0px"
                android:paddingTop="0px"
                android:paddingRight="0px">

    <com.unimelb.pt3.ui.TransparentPanel
            android:id="@+id/workbench" 
            android:layout_width="fill_parent"
            android:layout_height="10px"
            android:paddingTop="0px"
            android:paddingLeft="0px"
            android:paddingBottom="0px"
            android:paddingRight="0px">

        <GridView xmlns:android="http://schemas.android.com/apk/res/android" 
            android:id="@+id/gridview"
            android:layout_width="fill_parent" 
            android:layout_height="fill_parent"
            android:columnWidth="90dp"
            android:numColumns="auto_fit"
            android:verticalSpacing="10dp"
            android:horizontalSpacing="10dp"
            android:stretchMode="columnWidth"
            android:gravity="center" />

    </com.unimelb.pt3.ui.TransparentPanel>

</LinearLayout>

回答1:

the GridView has an invalidateViews() method.

when you call this method: "all the views to be rebuilt and redrawn." http://developer.android.com/reference/android/widget/GridView.html

i think this is what you need:)

回答2:

You must, first tell the adapter to notify that the data has changed and set the adapter again to the grid

adapter.notifyDataChanged();
grid.setAdapter(adapter);

回答3:

This may be helpful. I refresh a gridview of book image thumbnails after a delete is executed on an item. Using adapter.notifyDataChanged(); as mentioned above didn't work for me as it's called in my adapter.

//this is a call that retrieves cached data.
//your constructor can be designed and used without it.
final Object data = getLastNonConfigurationInstance();

I essentially just reload the adapter and bind it to the same view.

//reload the adapter
adapter = new BooksAdapter(MyBooks.this, MyBooks.this, data, show_collection );
grid.invalidateViews();
grid.setAdapter(adapter);

回答4:

@flyerz @snagnever

Together you guys have got it. It should be:

adapter.notifyDataChanged();
grid.invalidateViews();

This will flag the adapter that its data has changed, which will then be propagated to the grid whenever after the invalidateViews() method is called.

Glad I found this question because I could not figure out how to add items to the grid after its been rendered.

回答5:

None of these answers actually worked for me and I had to mash all of them together. To actually get the GridView to update, you need to do this:

 adapter.notifyDataChanged();
 grid.invalidateViews();
 grid.setAdapter(adapter);

Hope this helps anyone who couldn't get the other solutions to work.

回答6:

You should not call invalidateViews and setAdapter to refresh your grid view. This is not a good idea to keep your grid view updated, if you update in that way it would cost a lot of time and memory.

If you have a chance to look at getView method you will see that convertView is created just once. When you call notifyDataChanged, it will update this view. Whereas if you call invalidateViews, previously created views will be recreated. This is not a good solution.

Your getView method is called when you call notifyDataChanged. So your getView method should look something like the code below.

public List list;

public class SimpleItemViewHolder extends Object
{
    public TextView textView;
    public ImageView imageView;
}

public View getView(int position, View convertView, ViewGroup parent){

    View itemView = convertView;
    SimpleItemViewHolder viewHolder;

    if(convertView==null)
    {
        viewHolder = (SimpleItemViewHolder)itemView.getTag();

    }else{
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        itemView = inflater.inflate(R.layout.layout_name, null);
        TextView labelField = (TextView) itemView.findViewById(R.id.label_field);
        labelField.setText(list.get(position).Name);
        //Typeface boldFont = Typeface.createFromAsset(context.getAssets(), "fonts/Font-Bold.ttf");
        //labelField.setTypeface(boldFont);

        ImageView imageView = (ImageView) itemView.findViewById(R.id.image_view);
        //Bitmap bitmap = init your bitmap here;
        //imageView.setImageBitmap(bitmap);  

        viewHolder = new SimpleItemViewHolder();
        viewHolder.imageView = imageView;
        viewHolder.textView = labelField;
        itemView.setTag(viewHolder);

    }

    //don't create new views, instead use previous ones and update them.
    viewHolder.textView.setText(list.get(position).Name);
    //viewHolder.imageView.setImageBitmap(your_bitmap);  
    return itemView;
}

回答7:

adapter.notifyDataChanged();

may not works just because data for the adapter is stale (if Activity or fragment was not destroyed and have been sitting in the back stack for instance).

So, if firstly refresh data, then after it will be working.

回答8:

You are placing the GridView inside com.unimelb.pt3.ui.TransparentPanel which is 10px tall.

• You shouldn't use px, you should use dp.
• Change com.unimelb.pt3.ui.TransparentPanel's android:layout_height="10px" to android:layout_height="fill_parent"

回答9:

In your adapter :

class MAdapter extends BaseAdapter{
   List<Objects> mObjects;
...

 public void clearAdapter(){
        mObjects.clear();
    }

 public void addNewValues(List<Objects> mObjects){
        this.mObjects = mObjects;
    }

...

}


adapter.clearAdapter(); // clear old values
adapter.addNewValues(MObjects);
adapter.notifyDataChanged();