HelloGallery, using Gallery Widget.

Here is a exercise to implement a picture view using Gallery, a view that shows items in a center-locked, horizontally scrolling list.



Basically, this exercise follow the Android Tutorial, Hello Gallery. But in my practice, error is complained in building. I have to create a attrs.xml and modify some code to fix it.

Here is how I fix it to make it work.

Create a Android Application, HelloGallery. Copy some images, in .png format, into res/drawable/ directory. Named image_01..05.png in my case.

Android supports bitmap resource files in a few different formats: png (preferred), jpg (acceptable), gif (discouraged). The bitmap file itself is compiled and referenced by the file name without the extension (so res/drawable/my_picture.png would be referenced as R.drawable.my_picture).

Create res/values/attrs.xml to define Theme_android_galleryItemBackground.

<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="Theme">
<attr name="android:galleryItemBackground" />
</declare-styleable>
</resources>

Modify main.xml to have a Gallery in the screen.

<?xml version="1.0" encoding="utf-8"?>
<Gallery xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/gallery"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>

Finally, modify the HelloGallery.java

package com.exercise.HelloGallery;

import android.app.Activity;
import android.content.Context;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;

public class HelloGallery extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.main);

   Gallery g = (Gallery) findViewById(R.id.gallery);
   g.setAdapter(new ImageAdapter(this));

   g.setOnItemClickListener(new OnItemClickListener() {
       public void onItemClick(AdapterView<?> parent,
           View v, int position, long id) {
           Toast.makeText(HelloGallery.this, "" + position,
               Toast.LENGTH_SHORT).show();
       }
   });
}

public class ImageAdapter extends BaseAdapter {
   int mGalleryItemBackground;
   private Context mContext;

   private Integer[] mImageIds = {
           R.drawable.image_01,
           R.drawable.image_02,
           R.drawable.image_03,
           R.drawable.image_04,
           R.drawable.image_05
   };

   public ImageAdapter(Context c) {
       mContext = c;
       TypedArray a = obtainStyledAttributes(R.styleable.Theme);
       mGalleryItemBackground = a.getResourceId(
         R.styleable.Theme_android_galleryItemBackground,
                   0);
       a.recycle();
   }

   public int getCount() {
       return mImageIds.length;
   }

   public Object getItem(int position) {
       return position;
   }

   public long getItemId(int position) {
       return position;
   }

   public View getView(int position,
       View convertView, ViewGroup parent) {
       ImageView i = new ImageView(mContext);

       i.setImageResource(mImageIds[position]);
       i.setLayoutParams(new Gallery.LayoutParams(150, 100));
       i.setScaleType(ImageView.ScaleType.FIT_XY);
       i.setBackgroundResource(mGalleryItemBackground);

       return i;
   }
}
}

The project files, include some images for demo, can be downloaded here.

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