Android多媒体学习十一：实现仿百度图片查看功能

我们知道，进入百度图片后，输入一个关键字后，首先看到的是很多缩略图，当我们点击某张缩略图时，我们就可以进入到大图显示页面，在

大图显示页面，中包含了一个图片画廊，同时当前大图为刚刚我们点击的那张图片。现在我们看看在Android中如何实现类似的效果：

首先，我们需要有一个控件来显示缩略图，这里没有什么比GridView更加合适了。

配置文件如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<GridView
android:id="@+id/view_photos"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_marginTop="10dp"
android:columnWidth="100dp"
android:numColumns="auto_fit"
android:horizontalSpacing="5dp"
android:verticalSpacing="5dp"
android:listSelector="@drawable/frame_select" />
</LinearLayout>

对于GridView中每一项是一张缩略图，我们需要继承BaseAdapter，实现自己的一个GridImageAdapter，代码：

package com.liner.manager;
import java.util.List;
import com.liner.manager.adapter.GridImageAdapter;
import android.app.Activity;
import android.graphics.Bitmap;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Gallery;
import android.widget.ImageButton;
import android.widget.AdapterView.OnItemClickListener;
public class GalleryActivity extends Activity{

private ImageButton currentImage;
private Gallery gallery;

private int[] thumbIds;
private int currentPos;

private Bitmap currentBitmap;

private List<Bitmap> bitmapCache;

public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.gallery);

currentImage = (ImageButton)this.findViewById(R.id.image_current);
gallery = (Gallery)this.findViewById(R.id.image_gallery);
gallery.setOnItemClickListener(galleryItemClickListener);
init();
}

private OnItemClickListener galleryItemClickListener = new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> p, View v, int position,
long id) {
// 点击事件
showCurrentImage(position);
}
};

private void init(){
thumbIds = this.getIntent().getIntArrayExtra("thumbIds");
currentPos = this.getIntent().getIntExtra("currentPos",0);
//galleryIds = this.getThumbnailIds(currentPos); //当前的gallery里的图片信息
bitmapCache = BitmapUtils.queryThumbnailListByIds(this, thumbIds);
GridImageAdapter adapter = new GridImageAdapter(this.getApplication(), bitmapCache);
gallery.setAdapter(adapter);
gallery.setSelection(currentPos);

showCurrentImage(currentPos);

}

private void showCurrentImage(int position){

if(currentBitmap != null){
currentBitmap.recycle();
}

currentBitmap = BitmapUtils.queryImageByThumbnailId(GalleryActivity.this, thumbIds[position]);
if(currentBitmap != null){
currentImage.setImageBitmap(currentBitmap);
}else{
//什么都不做
}

//releaseBitmaps();
}

/**
* 将Gallery当前可见的显示之前的3张，后3张缓存起来，其余的释放掉，这样是为了放置内存不够用
* 之所以前三张后三张，是为了Gallery可以滑动的更加顺畅
*/
private void releaseBitmaps(){
int start = gallery.getFirstVisiblePosition()-3; //缓存的起始位置
int end = gallery.getLastVisiblePosition()+3; //缓存的结束位置

Bitmap delBitmap;
for(int i=0; i<start; i++){
delBitmap = bitmapCache.get(i);
if(delBitmap != null){
bitmapCache.remove(i);
delBitmap.recycle();
}
}
for(int i=end+1; i<bitmapCache.size(); i++){
delBitmap = bitmapCache.get(i);
if(delBitmap != null){
bitmapCache.remove(i);
delBitmap.recycle();
}
}
}

/**
* 获取当前位置的前三个Id和后三个Id
* @param position
* @return
*/
private Integer[] getThumbnailIds(int position){
Integer[] ids = new Integer[]{0,0,0,0,0,0,0};
int currPos = 0;
//关于这里的处理，比较复杂
for(int i=3; i>0; i--){
if(position - i >= 0){
currPos = 3-i;
ids[currPos] = thumbIds[position-i];
}
}
ids[++currPos] = thumbIds[position]; //当前Id
//currGallerySelection = currPos;
//这样右边剩下的位置数就是7-currPos-1
for(int i=1; i<=6-currPos;i++){
if(position+i < thumbIds.length){
ids[currPos+i] = thumbIds[position+i];
}
}
return ids;
}
}

然后，我们就可以在Activity中通过查询MediaStore的多媒体图片库来查询所有的图片的缩略图，缩略图所在的位置是：

MediaStore.Images.Thumbnails。Activity代码如下：

package com.liner.manager;
import java.util.ArrayList;
import java.util.List;
import com.liner.manager.adapter.GridImageAdapter;
import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore;
import android.view.View;
import android.widget.Adapter;
import android.widget.AdapterView;
import android.widget.GridView;
import android.widget.Toast;
public class MainActivity extends Activity {
private GridView photoView;
private GridImageAdapter imageAdapter;

private Cursor cursor;
private int[] thumbIds;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

photoView = (GridView)this.findViewById(R.id.view_photos);
photoView.setOnItemClickListener(photoClickListener);

//showImages();
showThumbnails();
}

private void showThumbnails(){

cursor = BitmapUtils.queryThumbnails(this);
if(cursor.moveToFirst()){
List<Bitmap> bitmaps = new ArrayList<Bitmap>();
thumbIds = new int[cursor.getCount()];
for(int i=0; i<cursor.getCount();i++){
cursor.moveToPosition(i);
String currPath = cursor.getString(cursor.getColumnIndexOrThrow(MediaStore.Images.Thumbnails.DATA));
thumbIds[i] = cursor.getInt(cursor.getColumnIndexOrThrow(MediaStore.Images.Thumbnails._ID));
Bitmap b = BitmapUtils.decodeBitmap(currPath,100,100);
bitmaps.add(b);
}
imageAdapter = new GridImageAdapter(this.getApplication(), bitmaps);
photoView.setAdapter(imageAdapter);
}
}

private AdapterView.OnItemClickListener photoClickListener = new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> p, View v, int position,
long id) {
//点击某张缩略图时，转到图片显示界面
Intent intent = new Intent();
intent.setClass(MainActivity.this, GalleryActivity.class);
intent.putExtra("thumbIds", thumbIds);
intent.putExtra("currentPos", position);
startActivity(intent);
}
};
}

注意到，我们记录了，所有缩略图对应的id号，和当前的用户选择的位置，然后通过Intent传递到第二个展示界面。第二个界面的布局文件如下：我们用了一个Gallery和一个ImageButton来实现

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical">
<Gallery
android:id="@+id/image_gallery"
android:layout_width="fill_parent"
android:layout_height="100dp"
/>
<ImageButton
android:id="@+id/image_current"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="10dp"
android:layout_marginTop="10dp"
/>
</LinearLayout>

然后，对应的Activity如下：

package com.liner.manager;
import java.util.List;
import com.liner.manager.adapter.GridImageAdapter;
import android.app.Activity;
import android.graphics.Bitmap;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Gallery;
import android.widget.ImageButton;
import android.widget.AdapterView.OnItemClickListener;
public class GalleryActivity extends Activity{

private ImageButton currentImage;
private Gallery gallery;

private int[] thumbIds;
private int currentPos;

private Bitmap currentBitmap;

private List<Bitmap> bitmapCache;

public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.gallery);

currentImage = (ImageButton)this.findViewById(R.id.image_current);
gallery = (Gallery)this.findViewById(R.id.image_gallery);
gallery.setOnItemClickListener(galleryItemClickListener);
init();
}

private OnItemClickListener galleryItemClickListener = new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> p, View v, int position,
long id) {
// 点击事件
showCurrentImage(position);
}
};

private void init(){
thumbIds = this.getIntent().getIntArrayExtra("thumbIds");
currentPos = this.getIntent().getIntExtra("currentPos",0);
//galleryIds = this.getThumbnailIds(currentPos); //当前的gallery里的图片信息
bitmapCache = BitmapUtils.queryThumbnailListByIds(this, thumbIds);
GridImageAdapter adapter = new GridImageAdapter(this.getApplication(), bitmapCache);
gallery.setAdapter(adapter);
gallery.setSelection(currentPos);

showCurrentImage(currentPos);

}

private void showCurrentImage(int position){

if(currentBitmap != null){
currentBitmap.recycle();
}

currentBitmap = BitmapUtils.queryImageByThumbnailId(GalleryActivity.this, thumbIds[position]);
if(currentBitmap != null){
currentImage.setImageBitmap(currentBitmap);
}else{
//什么都不做
}

//releaseBitmaps();
}
}

可以看到，当用户点击Gallery中某一项时，触发onItemClick事件，在其中，我们通过根据该缩略图对应的Image_ID来从MediaStore.Images.Media中查询该缩略图对应的大图。并在ImageButton中显示。

这里当图片很多时，可能会出现内存溢出，为了避免这种情况，可以更加Gallery的特点，使用缓存。保存当前可见的缩略图的前三个到后三个。其余的全部recycle。当用户点击Gallery的时候，在判断当前的位置，如果大于或小于某个值时，则重新更新缓存。这样保证内存中的缩略图的个数总是6+Gallery.getLastVisiblePosition-Gallery.getFirstVisiblePosition个。其实这就是浮动缓存窗口，一个固定大小窗口在整个坐标（全部缩略图）上游动。这里没有实现，以后待续。

同时，你可能已经注意到，程序中使用到了一个BitmapUtils类，这个类是封装了一系列对查询图片，并将其解析为Bitmap的类。

代码如下：

package com.liner.manager;
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.provider.MediaStore;
import android.util.Log;
public final class BitmapUtils {

public static Bitmap decodeBitmap(String path, int displayWidth, int displayHeight){
BitmapFactory.Options op = new BitmapFactory.Options();
op.inJustDecodeBounds = true;
Bitmap bmp = BitmapFactory.decodeFile(path, op); //获取尺寸信息
//获取比例大小
int wRatio = (int)Math.ceil(op.outWidth/(float)displayWidth);
int hRatio = (int)Math.ceil(op.outHeight/(float)displayHeight);
//如果超出指定大小，则缩小相应的比例
if(wRatio > 1 && hRatio > 1){
if(wRatio > hRatio){
op.inSampleSize = wRatio;
}else{
op.inSampleSize = hRatio;
}
}
op.inJustDecodeBounds = false;
bmp = BitmapFactory.decodeFile(path, op);
return Bitmap.createScaledBitmap(bmp, displayWidth, displayHeight, true);
}

/**
* 采用复杂计算来决定缩放
* @param path
* @param maxImageSize
* @return
*/
public static Bitmap decodeBitmap(String path, int maxImageSize){
BitmapFactory.Options op = new BitmapFactory.Options();
op.inJustDecodeBounds = true;
Bitmap bmp = BitmapFactory.decodeFile(path, op); //获取尺寸信息
int scale = 1;
if(op.outWidth > maxImageSize || op.outHeight > maxImageSize){
scale = (int)Math.pow(2, (int)Math.round(Math.log(maxImageSize/(double)Math.max(op.outWidth, op.outHeight))/Math.log(0.5)));
}
op.inJustDecodeBounds = false;
op.inSampleSize = scale;
bmp = BitmapFactory.decodeFile(path, op);
return bmp;
}

public static Cursor queryThumbnails(Activity context){
String[] columns = new String[]{
MediaStore.Images.Thumbnails.DATA,
MediaStore.Images.Thumbnails._ID,
MediaStore.Images.Thumbnails.IMAGE_ID
};
return context.managedQuery(MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI, columns, null, null, MediaStore.Images.Thumbnails.DEFAULT_SORT_ORDER);
}

public static Cursor queryThumbnails(Activity context, String selection, String[] selectionArgs){
String[] columns = new String[]{
MediaStore.Images.Thumbnails.DATA,
MediaStore.Images.Thumbnails._ID,
MediaStore.Images.Thumbnails.IMAGE_ID
};
return context.managedQuery(MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI, columns, selection, selectionArgs, MediaStore.Images.Thumbnails.DEFAULT_SORT_ORDER);
}

public static Bitmap queryThumbnailById(Activity context, int thumbId){
String selection = MediaStore.Images.Thumbnails._ID + " = ?";
String[] selectionArgs = new String[]{
thumbId+""
};
Cursor cursor = BitmapUtils.queryThumbnails(context,selection,selectionArgs);

if(cursor.moveToFirst()){
String path = cursor.getString(cursor.getColumnIndexOrThrow(MediaStore.Images.Thumbnails.DATA));
cursor.close();
return BitmapUtils.decodeBitmap(path, 100, 100);
}else{
cursor.close();
return null;
}
}

public static Bitmap[] queryThumbnailsByIds(Activity context, Integer[] thumbIds){
Bitmap[] bitmaps = new Bitmap[thumbIds.length];
for(int i=0; i<bitmaps.length; i++){
bitmaps[i] = BitmapUtils.queryThumbnailById(context, thumbIds[i]);
}

return bitmaps;
}

/**
* 获取全部
* @param context
* @return
*/
public static List<Bitmap> queryThumbnailList(Activity context){
List<Bitmap> bitmaps = new ArrayList<Bitmap>();
Cursor cursor = BitmapUtils.queryThumbnails(context);
for(int i=0; i<cursor.getCount(); i++){
cursor.moveToPosition(i);
String path = cursor.getString(cursor.getColumnIndexOrThrow(MediaStore.Images.Thumbnails.DATA));
Bitmap b = BitmapUtils.decodeBitmap(path, 100, 100);
bitmaps.add(b);
}
cursor.close();
return bitmaps;
}

public static List<Bitmap> queryThumbnailListByIds(Activity context, int[] thumbIds){
List<Bitmap> bitmaps = new ArrayList<Bitmap>();
for(int i=0; i<thumbIds.length; i++){
Bitmap b = BitmapUtils.queryThumbnailById(context, thumbIds[i]);
bitmaps.add(b);
}

return bitmaps;
}

public static Cursor queryImages(Activity context){
String[] columns = new String[]{
MediaStore.Images.Media._ID,
MediaStore.Images.Media.DATA,
MediaStore.Images.Media.DISPLAY_NAME
};
return context.managedQuery(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, columns, null, null, MediaStore.Images.Media.DEFAULT_SORT_ORDER);
}

public static Cursor queryImages(Activity context, String selection, String[] selectionArgs){
String[] columns = new String[]{
MediaStore.Images.Media._ID,
MediaStore.Images.Media.DATA,
MediaStore.Images.Media.DISPLAY_NAME
};
return context.managedQuery(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, columns, selection, selectionArgs, MediaStore.Images.Media.DEFAULT_SORT_ORDER);
}

public static Bitmap queryImageById(Activity context, int imageId){
String selection = MediaStore.Images.Media._ID + "=?";
String[] selectionArgs = new String[]{
imageId + ""
};
Cursor cursor = BitmapUtils.queryImages(context, selection, selectionArgs);
if(cursor.moveToFirst()){
String path = cursor.getString(cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA));
cursor.close();
//return BitmapUtils.decodeBitmap(path, 260, 260);
return BitmapUtils.decodeBitmap(path, 220); //看看和上面这种方式的差别,看了，差不多
}else{
cursor.close();
return null;
}
}

/**
* 根据缩略图的Id获取对应的大图
* @param context
* @param thumbId
* @return
*/
public static Bitmap queryImageByThumbnailId(Activity context, Integer thumbId){

String selection = MediaStore.Images.Thumbnails._ID + " = ?";
String[] selectionArgs = new String[]{
thumbId+""
};
Cursor cursor = BitmapUtils.queryThumbnails(context, selection, selectionArgs);

if(cursor.moveToFirst()){
int imageId = cursor.getInt(cursor.getColumnIndexOrThrow(MediaStore.Images.Thumbnails.IMAGE_ID));
cursor.close();
return BitmapUtils.queryImageById(context, imageId);
}else{
cursor.close();
return null;
}
}
}

这样就实现了，类似百度图片浏览的效果。效果图如下：