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大图查看器是许多app的常用功能,主要使用场景是用户点击图片,然后启动一个新界面来展示完整尺寸的图片,并能通过手势移动图片以及放大缩小。当然,上面说的是最基本的功能,实际使用中还要包括:如果是本地图片应该可以移除,如果是网络图片,应提供一个保存到本地的功能等。
本文为什么叫封装一个大图查看器,而不是叫做编写一个大图查看器呢?因为大图查看器的最核心功能,展示图片以及手势操控我们使用了一个开源库来完成,这个开源库叫做subsampling-scale-image-view,sciv非常靠谱,使用也非常简单,我记得知乎的Android app也是使用了它。这个库的Github地址是:。
我先把我做出来的效果图展示出来:
首先第一张是:
然后来看第二张:
两张界面截图展示的是同一张图片,但区别在于,第一张图片右下角有一个下载的图标,对应的是查看网络图片这种方式(大家都需要保存网络图片到本地这个功能);而第二张图片右下角没有了图标,而右上角有一个垃圾桶的图标,用来进行移除操作,想象一下,本来查看的就是本地图片,那用户也就不用再保存它一次了,而移除操作在很多实际使用场景中有效,比如说在微信中,你想发朋友圈,你选择了几张本地照片以后进行大图查看,而这时候你发现其中几张不太好,想移除它,于是为了用户方便,应该给用户提供一个在大图查看器中进行移除的方法。
代码很简单,唯一值得说的地方就是,里面放置了三个ImageView,分别作为:关闭Dialog,移除图片,保存图片到本地三个功能的按钮。
public class ScaleImageView { private static final byte URLS = 0;//网络查看状态 private static final byte FILES = 1;//本地查看状态 private byte status;//用来表示当前大图查看器的状态 private Activity activity; private List首先,我们关注一下最上面三行定义的几个变量,URLS和FILES两个常量分别表示网络查看模式和本地查看模式,而status则用来标示现在查看器处于哪个模式下。urls;//网络查看状态中传入的要查看的图片的Url的List private List files;//本地查看状态中传入的要查看的图片对应的file对象的List private List downloadFiles;//网络查看状态中从Url下载下来的图片对应的Url的List private int selectedPosition;//表示当前被选中的ViewPager的item的位置 private Dialog dialog;//用于承载整个大图查看器的Dialog private ImageView delete;//删除图片的按钮 private ImageView download;//保存图片到本地的按钮 private TextView imageCount;//用于显示当前正在查看第几张图片的TextView private ViewPager viewPager; private List views;//ViewPager适配器的数据源 private MyPagerAdapter adapter; private OnDeleteItemListener listener; private int startPosition;//打开大图查看器时,想要查看的ViewPager的item的位置 public ScaleImageView(Activity activity) { this.activity = activity; init(); } public void setOnDeleteItemListener(OnDeleteItemListener listener) { this.listener = listener; } private void init() { RelativeLayout relativeLayout = (RelativeLayout) activity.getLayoutInflater().inflate(R.layout.dialog_scale_image, null); ImageView close = (ImageView) relativeLayout.findViewById(R.id.scale_image_close); delete = (ImageView) relativeLayout.findViewById(R.id.scale_image_delete); download = (ImageView) relativeLayout.findViewById(R.id.scale_image_save); imageCount = (TextView) relativeLayout.findViewById(R.id.scale_image_count); viewPager = (ViewPager) relativeLayout.findViewById(R.id.scale_image_view_pager); dialog = new Dialog(activity, R.style.Dialog_Fullscreen); dialog.setContentView(relativeLayout); close.setOnClickListener(v -> dialog.dismiss()); delete.setOnClickListener(v -> { int size = views.size(); files.remove(selectedPosition); if (listener != null) { listener.onDelete(selectedPosition); } viewPager.removeView(views.remove(selectedPosition)); if (selectedPosition != size) { int position = selectedPosition + 1; String text = position + "/" + views.size(); imageCount.setText(text); } adapter.notifyDataSetChanged(); }); download.setOnClickListener(v -> { try { MediaStore.Images.Media.insertImage(activity.getContentResolver(), downloadFiles.get(selectedPosition).getAbsolutePath(), downloadFiles.get(selectedPosition).getName(), null); } catch (FileNotFoundException e) { e.printStackTrace(); } Snackbar.make(viewPager, "图片保存成功", Snackbar.LENGTH_SHORT).show(); }); viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() { @Override public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { } @Override public void onPageSelected(int position) { selectedPosition = position; String text = ++position + "/" + views.size(); imageCount.setText(text); } @Override public void onPageScrollStateChanged(int state) { } }); }}
public interface OnDeleteItemListener { void onDelete(int position); }这个接口的作用在于,当调用者在移除了某张图片后,还需要做的事情就应该写在接口的onDelete方法中。举个例子,假如你用了一个GridView来展示9张图片,当用户在大图查看器中将第3张图片移除的时候,这个时候你的GridView应该和大图查看器保持一致,也把第三张图片移除掉,而GridView的移除逻辑,就应该写在onDelete方法中。
public void setUrls(List当调用者想使用网络查看模式的时候,应该使用第一个方法——setUrls。调用者需要传入想要查看的这组图片的url并传入起始查看位置,举例来说,当调用者使用GridView来为用户展示图片的时候,用户可能点击了GridView的第三张图片,他想从第三张开始看起,而这第二个参数就是指的这个。后面的逻辑包括给类设置状态,即给status的值设置为URLS,然后清空或者初始化下载的图片,并给imageCount设置正确的显示内容。而setFiles也是类似的,我就不展开讲了,大致就是,要查看本地图片,调用者应该拿到本地图片的File对象并装入一个List然后传入。urls, int startPosition) { if (this.urls == null) { this.urls = new ArrayList<>(); } else { this.urls.clear(); } this.urls.addAll(urls); status = URLS; delete.setVisibility(View.GONE); if (downloadFiles == null) { downloadFiles = new ArrayList<>(); } else { downloadFiles.clear(); } this.startPosition = startPosition++; String text = startPosition + "/" + urls.size(); imageCount.setText(text); } public void setFiles(List files, int startPosition) { if (this.files == null) { this.files = new LinkedList<>(); } else { this.files.clear(); } this.files.addAll(files); status = FILES; download.setVisibility(View.GONE); this.startPosition = startPosition++; String text = startPosition + "/" + files.size(); imageCount.setText(text); }
public void create() { dialog.show(); views = new ArrayList<>(); adapter = new MyPagerAdapter(views, dialog); if (status == URLS) { for (String url : urls) { FrameLayout frameLayout = (FrameLayout) activity.getLayoutInflater().inflate(R.layout.view_scale_image, null); SubsamplingScaleImageView imageView = (SubsamplingScaleImageView) frameLayout.findViewById(R.id.scale_image_view); views.add(frameLayout); IOThread.getSingleThread().execute(() -> { File downLoadFile; try { downLoadFile = Glide.with(activity).load(url).downloadOnly(Target.SIZE_ORIGINAL, Target.SIZE_ORIGINAL).get(); downloadFiles.add(downLoadFile); activity.runOnUiThread(() -> imageView.setImage(ImageSource.uri(Uri.fromFile(downLoadFile)))); } catch (Exception e) { e.printStackTrace(); } }); } viewPager.setAdapter(adapter); } else if (status == FILES) { for (File file : files) { FrameLayout frameLayout = (FrameLayout) activity.getLayoutInflater().inflate(R.layout.view_scale_image, null); SubsamplingScaleImageView imageView = (SubsamplingScaleImageView) frameLayout.findViewById(R.id.scale_image_view); views.add(frameLayout); imageView.setImage(ImageSource.uri(Uri.fromFile(file))); } viewPager.setAdapter(adapter); } viewPager.setCurrentItem(startPosition); }首先,这里要将Dialog显示出来,然后初始化ViewPager的Adapter,Adapter的代码如下所示:
private static class MyPagerAdapter extends PagerAdapter { private List这是一个很简单的ViewPager适配器,唯一要说明的就是复写的destroyItem这个方法,它里面对应了多种情况,例如,当图片只有一张的时候,当移除的图片是一组图片的最后一张的时候,这些都要做相映的判断,否则使用的时候都会发生异常。views; private Dialog dialog; MyPagerAdapter(List views, Dialog dialog) { this.views = views; this.dialog = dialog; } @Override public Object instantiateItem(ViewGroup container, int position) { container.addView(views.get(position)); return views.get(position); } @Override public void destroyItem(ViewGroup container, int position, Object object) { if (position == 0 && views.size() == 0) { dialog.dismiss(); return; } if (position == views.size()) { container.removeView(views.get(--position)); } else { container.removeView(views.get(position)); } } @Override public int getCount() { return views.size(); } @Override public boolean isViewFromObject(View view, Object object) { return view == object; } @Override public int getItemPosition(Object object) { return POSITION_NONE; } }
ScaleImageView scaleImageView = new ScaleImageView(activity);scaleImageView.setUrls(urls, position);scaleImageView.create();如果查看本地图片:
ScaleImageView scaleImageView = new ScaleImageView(activity);scaleImageView.setFiles(files, position);scaleImageView.setOnDeleteItemListener(deletePosition -> adapter.removeItem(deletePosition));scaleImageView.create();最后附上完整的java代码,一共也就两百多行,很简单:
public class ScaleImageView { private static final byte URLS = 0; private static final byte FILES = 1; private byte status; private Activity activity; private Listurls; private List files; private List downloadFiles; private int selectedPosition; private Dialog dialog; private ImageView delete; private ImageView download; private TextView imageCount; private ViewPager viewPager; private List views; private MyPagerAdapter adapter; private OnDeleteItemListener listener; private int startPosition; public ScaleImageView(Activity activity) { this.activity = activity; init(); } public void setUrls(List urls, int startPosition) { if (this.urls == null) { this.urls = new ArrayList<>(); } else { this.urls.clear(); } this.urls.addAll(urls); status = URLS; delete.setVisibility(View.GONE); if (downloadFiles == null) { downloadFiles = new ArrayList<>(); } else { downloadFiles.clear(); } this.startPosition = startPosition++; String text = startPosition + "/" + urls.size(); imageCount.setText(text); } public void setFiles(List files, int startPosition) { if (this.files == null) { this.files = new LinkedList<>(); } else { this.files.clear(); } this.files.addAll(files); status = FILES; download.setVisibility(View.GONE); this.startPosition = startPosition++; String text = startPosition + "/" + files.size(); imageCount.setText(text); } public void setOnDeleteItemListener(OnDeleteItemListener listener) { this.listener = listener; } private void init() { RelativeLayout relativeLayout = (RelativeLayout) activity.getLayoutInflater().inflate(R.layout.dialog_scale_image, null); ImageView close = (ImageView) relativeLayout.findViewById(R.id.scale_image_close); delete = (ImageView) relativeLayout.findViewById(R.id.scale_image_delete); download = (ImageView) relativeLayout.findViewById(R.id.scale_image_save); imageCount = (TextView) relativeLayout.findViewById(R.id.scale_image_count); viewPager = (ViewPager) relativeLayout.findViewById(R.id.scale_image_view_pager); dialog = new Dialog(activity, R.style.Dialog_Fullscreen); dialog.setContentView(relativeLayout); close.setOnClickListener(v -> dialog.dismiss()); delete.setOnClickListener(v -> { int size = views.size(); files.remove(selectedPosition); if (listener != null) { listener.onDelete(selectedPosition); } viewPager.removeView(views.remove(selectedPosition)); if (selectedPosition != size) { int position = selectedPosition + 1; String text = position + "/" + views.size(); imageCount.setText(text); } adapter.notifyDataSetChanged(); }); download.setOnClickListener(v -> { try { MediaStore.Images.Media.insertImage(activity.getContentResolver(), downloadFiles.get(selectedPosition).getAbsolutePath(), downloadFiles.get(selectedPosition).getName(), null); } catch (FileNotFoundException e) { e.printStackTrace(); } Snackbar.make(viewPager, "图片保存成功", Snackbar.LENGTH_SHORT).show(); }); viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() { @Override public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { } @Override public void onPageSelected(int position) { selectedPosition = position; String text = ++position + "/" + views.size(); imageCount.setText(text); } @Override public void onPageScrollStateChanged(int state) { } }); } public void create() { dialog.show(); views = new ArrayList<>(); adapter = new MyPagerAdapter(views, dialog); if (status == URLS) { for (String url : urls) { FrameLayout frameLayout = (FrameLayout) activity.getLayoutInflater().inflate(R.layout.view_scale_image, null); SubsamplingScaleImageView imageView = (SubsamplingScaleImageView) frameLayout.findViewById(R.id.scale_image_view); views.add(frameLayout); IOThread.getSingleThread().execute(() -> { File downLoadFile; try { downLoadFile = Glide.with(activity).load(url).downloadOnly(Target.SIZE_ORIGINAL, Target.SIZE_ORIGINAL).get(); downloadFiles.add(downLoadFile); activity.runOnUiThread(() -> imageView.setImage(ImageSource.uri(Uri.fromFile(downLoadFile)))); } catch (Exception e) { e.printStackTrace(); } }); } viewPager.setAdapter(adapter); } else if (status == FILES) { for (File file : files) { FrameLayout frameLayout = (FrameLayout) activity.getLayoutInflater().inflate(R.layout.view_scale_image, null); SubsamplingScaleImageView imageView = (SubsamplingScaleImageView) frameLayout.findViewById(R.id.scale_image_view); views.add(frameLayout); imageView.setImage(ImageSource.uri(Uri.fromFile(file))); } viewPager.setAdapter(adapter); } viewPager.setCurrentItem(startPosition); } private static class MyPagerAdapter extends PagerAdapter { private List views; private Dialog dialog; MyPagerAdapter(List views, Dialog dialog) { this.views = views; this.dialog = dialog; } @Override public Object instantiateItem(ViewGroup container, int position) { container.addView(views.get(position)); return views.get(position); } @Override public void destroyItem(ViewGroup container, int position, Object object) { if (position == 0 && views.size() == 0) { dialog.dismiss(); return; } if (position == views.size()) { container.removeView(views.get(--position)); } else { container.removeView(views.get(position)); } } @Override public int getCount() { return views.size(); } @Override public boolean isViewFromObject(View view, Object object) { return view == object; } @Override public int getItemPosition(Object object) { return POSITION_NONE; } } public interface OnDeleteItemListener { void onDelete(int position); }}