Android 图片预览器加载微博长图，大图

通常图片预览的做法是ViewPager+PhotoView，但是遇到很长的图（比如微博长图），在设置

 android:scaleType="centerCrop"

这个属性的前提下

用ImageLoader 加载会比较模糊（应该是压缩的比较厉害），不设置这个属性，长图不能放大。用Glide加载，虽然就能清楚加载，但是不能滑动。那怎么办呢？

好在GitHub上又大神给我提供了subsampling-scale-image-view，上面介绍了基本用法，这个View能很好的加载长图的问题，在配合Glide的使用，完美的展现一个高效的图片预览，首先添加依赖：

compile 'com.github.bumptech.glide:glide:3.6.1'

 compile 'com.davemorrissey.labs:subsampling-scale-image-view:3.5.0'

创建一个包含此View的布局：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:background="#ff000000">

    <uk.co.senab.photoview.PhotoView
        android:id="@+id/zoom_image_view"
        android:layout_width="match_parent"
        android:scaleType="centerCrop"
        android:visibility="gone"
        android:layout_height="match_parent" />

    <com.davemorrissey.labs.subscaleview.SubsamplingScaleImageView
        android:id="@+id/imageView"
        android:layout_width="match_parent"
        app:quickScaleEnabled="true"
        android:layout_height="match_parent"/>

    <ProgressBar
        android:id="@+id/loading"
        android:layout_width="30dp"
        android:layout_height="30dp"
        android:visibility="gone"
        android:layout_gravity="center" />
</FrameLayout>

核心代码：

 View view = inflater.inflate(R.layout.content_picture_preview,container,false);
            //View view = inflater.inflate(R.layout.content_picture_preview, container, false);
            //final PhotoView photoView = (PhotoView) view.findViewById(R.id.zoom_image_view) ;
           // photoView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            //final ProgressBar spinner = (ProgressBar) view.findViewById(R.id.loading);
            //photoView.setBackgroundColor(0xff000000);
            String imagePath = mPaths.get(position);
            final SubsamplingScaleImageView imageView =  (SubsamplingScaleImageView)view.findViewById(R.id.imageView);
            //手势回调
            gestureDetector = new GestureDetector(PicturePreviewActivity.this, new GestureDetector.SimpleOnGestureListener() {
                @Override
                public boolean onSingleTapConfirmed(MotionEvent e) {
                    if (imageView.isReady()) {
                        PointF sCoord = imageView.viewToSourceCoord(e.getX(), e.getY());
                        Toast.makeText(getApplicationContext(), "单击: " + ((int) sCoord.x) + ", " + ((int) sCoord.y),
                                Toast.LENGTH_SHORT).show();
                    } else {
                       // Toast.makeText(getApplicationContext(), fail_tips, Toast.LENGTH_SHORT).show();
                    }

                    return false;
                }

                @Override
                public void onLongPress(MotionEvent e) {
                    if (imageView.isReady()) {
                        PointF sCoord = imageView.viewToSourceCoord(e.getX(), e.getY());
                        Toast.makeText(getApplicationContext(), "长按: " + ((int) sCoord.x) + ", " + ((int) sCoord.y),
                                Toast.LENGTH_SHORT).show();
                    } else {
                        //Toast.makeText(getApplicationContext(), fail_tips, Toast.LENGTH_SHORT).show();
                    }
                }

                @Override
                public boolean onDoubleTap(MotionEvent e) {
                    if (imageView.isReady()) {
                        PointF sCoord = imageView.viewToSourceCoord(e.getX(), e.getY());
                        Toast.makeText(getApplicationContext(), "双击: " + ((int) sCoord.x) + ", " + ((int) sCoord.y),
                                Toast.LENGTH_SHORT).show();
                    } else {
                        Toast.makeText(getApplicationContext(), "", Toast.LENGTH_SHORT).show();
                    }

                    return false;
                }
            });

            imageView.setOnTouchListener(new View.OnTouchListener() {
                @Override
                public boolean onTouch(View view, MotionEvent motionEvent) {
                    return gestureDetector.onTouchEvent(motionEvent);
                }
            });

           final int pos = position;
           // imageView.setMinimumScaleType(SubsamplingScaleImageView.SCALE_TYPE_CUSTOM);
            imageView.setMaxScale(15);
            imageView.setZoomEnabled(true);
           // spinner.setVisibility(View.GONE);
            imageView.setMinimumScaleType(SubsamplingScaleImageView.SCALE_TYPE_CUSTOM);
            Glide.with(mContext)
                    .load(imagePath).downloadOnly(new SimpleTarget<File>() {
                @Override
                public void onResourceReady(File resource, GlideAnimation<? super File> glideAnimation) {
                    // 将保存的图片地址给SubsamplingScaleImageView,这里注意设置ImageViewState设置初始显示比例
                    ImageSource imageSource = ImageSource.uri(Uri.fromFile(resource));
                   int  sWidth = BitmapFactory.decodeFile(resource.getAbsolutePath()).getWidth();
                    int sHeight = BitmapFactory.decodeFile(resource.getAbsolutePath()).getHeight();
                    WindowManager wm = (WindowManager) mContext
                            .getSystemService(Context.WINDOW_SERVICE);
                    int width = wm.getDefaultDisplay().getWidth();
                    int height = wm.getDefaultDisplay().getHeight();
                    float scale = SystemUtil.displaySize.x / (float) sWidth;
                    //float centerX = SystemUtil.displaySize.x / 2;
                   // imageView.setImage(ImageSource.uri(Uri.fromFile(resource)), new ImageViewState(2.0F, new PointF(0, 0), 0));
                    //imageView.setImage(ImageSource.uri(Uri.fromFile(resource)), new ImageViewState(2.0F, new PointF(0, 0), 0));
                  if (sHeight >= height
                            && sHeight / sWidth >=3) {
                        imageView.setMinimumScaleType(SubsamplingScaleImageView.SCALE_TYPE_CENTER_CROP);
                        imageView.setImage(ImageSource.uri(Uri.fromFile(resource)), new ImageViewState(2.0F, new PointF(0, 0), 0));
                    }else {
                       imageView.setMinimumScaleType(SubsamplingScaleImageView.SCALE_TYPE_CUSTOM);
                       imageView.setImage(ImageSource.uri(Uri.fromFile(resource)));
                       imageView.setDoubleTapZoomStyle(ZOOM_FOCUS_CENTER_IMMEDIATE);
                    }
                }});

Glide加载图片判断图片的宽高比例，来做相应的逻辑处理。通过

GestureDetector

来控制单击，双击，长按的逻辑控制。这样就能完美加载长图了，赶紧加入到的项目中吧！