Android Gallery是一个可以展示图片或者视频等多媒体内容的组件。它也是一个支持手势操作的滑动控件，用户可以通过滑动屏幕来切换图片等多媒体内容。在本文中，我们将从以下几个方面来对Android Gallery进行详细的阐述：
一、Gallery的基本使用
public class MainActivity extends Activity {
private Gallery mGallery;
private int[] mImageIds = new int[] {
R.drawable.img1,
R.drawable.img2,
R.drawable.img3,
R.drawable.img4,
R.drawable.img5
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mGallery = (Gallery) findViewById(R.id.gallery);
mGallery.setAdapter(new ImageAdapter(this));
}
private class ImageAdapter extends BaseAdapter {
private Context mContext;
public ImageAdapter(Context context) {
this.mContext = context;
}
@Override
public int getCount() {
return mImageIds.length;
}
@Override
public Object getItem(int position) {
return mImageIds[position];
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ImageView imageView = new ImageView(mContext);
imageView.setImageResource(mImageIds[position]);
imageView.setLayoutParams(new Gallery.LayoutParams(240, 180));
imageView.setScaleType(ImageView.ScaleType.FIT_XY);
return imageView;
}
}
}
以上代码展示了Gallery的基本使用方法，需要注意的是，我们需要为Gallery设置一个Adapter来为其提供数据，同时，我们也需要自定义Adapter来实现展示图片的效果。在这个例子中，我们创建了一个ImageAdapter类，重写了Adapter中的方法来实现图片展示，同时我们也为ImageView设置了LayoutParams和ScaleType。
二、Gallery的滑动特效
Android的Gallery控件具有多种滑动特效，包括平移、渐变、缩放等等。我们可以通过定义我们自己的Animation来实现Gallery的滑动特效。
public class MainActivity extends Activity {
private Gallery mGallery;
private int[] mImageIds = new int[] {
R.drawable.img1,
R.drawable.img2,
R.drawable.img3,
R.drawable.img4,
R.drawable.img5
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mGallery = (Gallery) findViewById(R.id.gallery);
mGallery.setAdapter(new ImageAdapter(this));
mGallery.setAnimationDuration(1000);
mGallery.setAnimation(new TranslateAnimation(0, 200, 0, 0));
}
private class ImageAdapter extends BaseAdapter {
private Context mContext;
public ImageAdapter(Context context) {
this.mContext = context;
}
@Override
public int getCount() {
return mImageIds.length;
}
@Override
public Object getItem(int position) {
return mImageIds[position];
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ImageView imageView = new ImageView(mContext);
imageView.setImageResource(mImageIds[position]);
imageView.setLayoutParams(new Gallery.LayoutParams(240, 180));
imageView.setScaleType(ImageView.ScaleType.FIT_XY);
return imageView;
}
}
}
在以上代码中，我们定义了一个TranslateAnimation对象，用来指定Gallery的滑动方向和距离。同时我们也通过setAnimationDuration方法来设置Gallery的滑动时间。
三、Gallery的点击事件
我们也可以为Gallery设置点击事件，当用户点击图片时可以进行特定操作。例如，在这个例子中，当用户点击图片时，我们将展示该图片的名称。
public class MainActivity extends Activity {
private Gallery mGallery;
private int[] mImageIds = new int[] {
R.drawable.img1,
R.drawable.img2,
R.drawable.img3,
R.drawable.img4,
R.drawable.img5
};
private String[] mImageNames = new String[] {
"图片1",
"图片2",
"图片3",
"图片4",
"图片5"
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mGallery = (Gallery) findViewById(R.id.gallery);
mGallery.setAdapter(new ImageAdapter(this));
mGallery.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView parent, View view, int position, long id) {
Toast.makeText(MainActivity.this, mImageNames[position], Toast.LENGTH_SHORT).show();
}
});
}
private class ImageAdapter extends BaseAdapter {
private Context mContext;
public ImageAdapter(Context context) {
this.mContext = context;
}
@Override
public int getCount() {
return mImageIds.length;
}
@Override
public Object getItem(int position) {
return mImageIds[position];
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ImageView imageView = new ImageView(mContext);
imageView.setImageResource(mImageIds[position]);
imageView.setLayoutParams(new Gallery.LayoutParams(240, 180));
imageView.setScaleType(ImageView.ScaleType.FIT_XY);
return imageView;
}
}
}
在以上代码中，我们重写了Gallery的OnItemClickListener方法，当用户点击某个图片时，我们通过Toast来展示该图片的名称。
四、Gallery的自定义布局
我们也可以为Gallery设置自定义布局，例如，在这个例子中，我们将为Gallery中每个图片添加一个TextView显示图片的名称。
public class MainActivity extends Activity {
private Gallery mGallery;
private int[] mImageIds = new int[] {
R.drawable.img1,
R.drawable.img2,
R.drawable.img3,
R.drawable.img4,
R.drawable.img5
};
private String[] mImageNames = new String[] {
"图片1",
"图片2",
"图片3",
"图片4",
"图片5"
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mGallery = (Gallery) findViewById(R.id.gallery);
mGallery.setAdapter(new ImageAdapter(this));
mGallery.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView parent, View view, int position, long id) {
Toast.makeText(MainActivity.this, mImageNames[position], Toast.LENGTH_SHORT).show();
}
});
}
private class ImageAdapter extends BaseAdapter {
private Context mContext;
public ImageAdapter(Context context) {
this.mContext = context;
}
@Override
public int getCount() {
return mImageIds.length;
}
@Override
public Object getItem(int position) {
return mImageIds[position];
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View view = LayoutInflater.from(mContext).inflate(R.layout.item_gallery, null);
ImageView imageView = (ImageView) view.findViewById(R.id.iv_image);
TextView textView = (TextView) view.findViewById(R.id.tv_name);
imageView.setImageResource(mImageIds[position]);
textView.setText(mImageNames[position]);
return view;
}
}
}
以上代码中，我们通过调用LayoutInflater的方法来加载自定义布局，并且在布局中添加了一个TextView来展示图片名称。
五、Gallery的性能优化
对于一些超大的图片或者视屏数据，在Gallery中进行展示可能会影响到应用的性能。在这种情况下，我们可以通过异步加载来进行性能优化。
public class MainActivity extends Activity {
private Gallery mGallery;
private int[] mImageIds = new int[] {
R.drawable.img1,
R.drawable.img2,
R.drawable.img3,
R.drawable.img4,
R.drawable.img5
};
private String[] mImageNames = new String[] {
"图片1",
"图片2",
"图片3",
"图片4",
"图片5"
};
private ImageLoader mImageLoader;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mGallery = (Gallery) findViewById(R.id.gallery);
mGallery.setAdapter(new ImageAdapter(this));
mGallery.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView parent, View view, int position, long id) {
Toast.makeText(MainActivity.this, mImageNames[position], Toast.LENGTH_SHORT).show();
}
});
mImageLoader = new ImageLoader();
}
private class ImageAdapter extends BaseAdapter {
private Context mContext;
public ImageAdapter(Context context) {
this.mContext = context;
}
@Override
public int getCount() {
return mImageIds.length;
}
@Override
public Object getItem(int position) {
return mImageIds[position];
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ImageView imageView;
if (convertView == null) {
imageView = new ImageView(mContext);
} else {
imageView = (ImageView) convertView;
}
imageView.setTag(mImageIds[position]);
mImageLoader.loadImage(mImageIds[position], imageView);
imageView.setLayoutParams(new Gallery.LayoutParams(240, 180));
imageView.setScaleType(ImageView.ScaleType.FIT_XY);
return imageView;
}
}
private class ImageLoader {
private SparseArray mBitmaps = new SparseArray<>();
public void loadImage(int resId, ImageView target) {
Bitmap bitmap = mBitmaps.get(resId);
if (bitmap != null) {
target.setImageBitmap(bitmap);
} else {
new LoadTask(resId, target).execute();
}
}
private class LoadTask extends AsyncTask
{
private int resId;
private ImageView target;
public LoadTask(int resId, ImageView target) {
this.resId = resId;
this.target = target;
}
@Override
protected Bitmap doInBackground(Void... params) {
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(getResources(), resId, options);
int width = options.outWidth;
int height = options.outHeight;
options.inSampleSize = Math.max(width / 240, height / 180);
options.inJustDecodeBounds = false;
Bitmap bitmap = BitmapFactory.decodeResource(getResources(), resId, options);
mBitmaps.put(resId, bitmap);
return bitmap;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
Object tag = target.getTag();
if (tag != null && tag instanceof Integer && (int) tag == resId) {
target.setImageBitmap(bitmap);
}
}
}
}
}
以上代码中，我们通过自定义ImageLoader类和LoadTask类来异步加载Gallery中的图片，同时也添加了一个缓存机制来提高性能。
