在一定范围里，按比例缩放图片，优化展示效果

在listview中，每个条目有一张图片，图片的大小是随机的，怎么展示才能美观。很多人用的方法是，在ImageView中，加属性

     android:adjustViewBounds="true"     android:maxHeight="300dp"     android:maxWidth="300dp"     android:minHeight="150dp"     android:minWidth="150dp"

用来限定ImageView的最大值和最小值。但是，这样展示的图片，很多时候会很丑。怎么才能像微信一样，有个范围，超过那个范围，就压缩，而且是按比例压缩。使得展示的很美观呢？
我不知道微信怎么写的，但是尽可能的模仿了。我们项目用的是xUtils3，我这里针对xUtils3写。其他理论上类似

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效果图：

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说明：
这里是模仿了微信的展示效果。宽或者高的最大值，不超过屏幕宽度值的一半。我自己设定了宽或者高的最小值，不小于屏幕宽度值的1/6。如上图的宝剑图。高是宽的17倍之多，但是高显示的最大值是屏幕宽的一半，如果此时宽还是它的17分之一，就没法看了。再比如最下面的猫图。宽高仅仅80像素。很小，如果按照原先的展示，也没法看

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代码：
1、核心代码：处理及展示的工具类：

package com.chen.demo;import android.app.Activity;import android.graphics.drawable.Drawable;import android.view.View;import android.widget.ImageView;import android.widget.LinearLayout;import android.widget.RelativeLayout;import android.widget.TextView;import org.xutils.common.Callback;import org.xutils.image.ImageOptions;import org.xutils.x;/** * Created by chen on 2016/10/20. */public class BitmapHelper {    public static void displayImg_Fit_XY(final ImageView imageView, String iconUrl, final RelativeLayout rl, final TextView longImgTv, String w, String h, final Activity act, TextView src_width_tv, TextView src_height_tv, TextView src_ratio_tv, TextView result_width_tv, TextView result_height_tv, TextView result_ratio_tv) {        if ("null".equals(iconUrl)) {            iconUrl = null;        }        try {            //宽高的计算结果            final int width_result;            final int height_result;            //原始的宽高值            final int width_src;            final int height_src;            int width = Integer.parseInt(w);            width_src = width;            int height = Integer.parseInt(h);            height_src = height;            //图片宽或者高的最大值。以屏幕一半为例。            int halfScreenSize = Utils.getScreenSize(act)[0] / 2;            //最小值。避免图片过小            int minSize = halfScreenSize / 3;            LinearLayout.LayoutParams rl_lp = new LinearLayout.LayoutParams(halfScreenSize / 2, halfScreenSize / 2);            /**             * Sets the margins, in pixels. A call to {@link android.view.View#requestLayout()} needs             * to be done so that the new margins are taken into account. Left and right margins may be             * overriden by {@link android.view.View#requestLayout()} depending on layout direction.             * Margin values should be positive.             *             * @param left the left margin size             * @param top the top margin size             * @param right the right margin size             * @param bottom the bottom margin size             *             * @attr ref android.R.styleable#ViewGroup_MarginLayout_layout_marginLeft             * @attr ref android.R.styleable#ViewGroup_MarginLayout_layout_marginTop             * @attr ref android.R.styleable#ViewGroup_MarginLayout_layout_marginRight             * @attr ref android.R.styleable#ViewGroup_MarginLayout_layout_marginBottom             */            rl_lp.setMargins(0, Utils.dp2px(act, 5), 0, 0);            rl.setLayoutParams(rl_lp);            RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams(halfScreenSize / 2, halfScreenSize / 2);            imageView.setLayoutParams(lp);            //宽高的比例            float ratio = 0;            if (width > halfScreenSize || height > halfScreenSize) {                //需要限制大小                if (width > height) {                    //横图。得到宽高比例                    ratio = 1.0f * height / width;                    if (width > halfScreenSize) {                        width = halfScreenSize;                    }                    height = (int) (width * ratio);                    if (height < minSize) {                        height = minSize;                    }                } else if (height >= width) {                    //竖图                    ratio = 1.0f * width / height;                    if (height > halfScreenSize) {                        height = halfScreenSize;                    }                    width = (int) (height * ratio);                    if (width < minSize) {                        width = minSize;                    }                }            } else {                //长和宽都没有超过屏幕的一半                if (width > height) {                    ratio = 1.0f * height / width;                    if (width < minSize) {                        width = minSize;                    }                    height = (int) (width * ratio);                    if (height < minSize) {                        height = minSize;                    }                } else {                    ratio = 1.0f * width / height;                    if (height < minSize) {                        height = minSize;                    }                    width = (int) (height * ratio);                    if (width < minSize) {                        width = minSize;                    }                }            }            width_result = width;            height_result = height;            src_width_tv.setText("原宽=" + width_src);            src_height_tv.setText("原高=" + height_src);            if (width_src > height_src) {                src_ratio_tv.setText("width / height=" + (1.0f * width_src / height_src));            } else {                src_ratio_tv.setText("height / width=" + (1.0f * height_src / width_src));            }            result_width_tv.setText("结果宽=" + width_result);            result_height_tv.setText("结果高=" + height_result);            if (width_result > height_result) {                result_ratio_tv.setText("结果-width / height=" + (1.0f * width_result / height_result));            } else {                result_ratio_tv.setText("结果-height / width=" + (1.0f * height_result / width_result));            }            ImageOptions imageOptions = new ImageOptions.Builder()                    .setIgnoreGif(true)                    .setImageScaleType(ImageView.ScaleType.FIT_XY)                    .setLoadingDrawableId(R.mipmap.loading)                    .setUseMemCache(true)                    .build();            x.image().bind(imageView, iconUrl, imageOptions, new Callback.CommonCallback<Drawable>() {                @Override                public void onSuccess(Drawable arg0) {                    //宽是高的3倍，或者高是宽的3倍。就视为长图                    if (width_src / height_src >= 3 || height_src / width_src >= 3) {                        longImgTv.setVisibility(View.VISIBLE);                    } else {                        longImgTv.setVisibility(View.GONE);                    }                    LinearLayout.LayoutParams rl_lp = new LinearLayout.LayoutParams(width_result, height_result);                    rl_lp.setMargins(0, Utils.dp2px(act, 5), 0, 0);                    rl.setLayoutParams(rl_lp);                    RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams(width_result, height_result);                    imageView.setLayoutParams(lp);                }                @Override                public void onFinished() {                }                @Override                public void onError(Throwable arg0, boolean arg1) {                    imageView.setBackgroundResource(R.mipmap.loadfailed);                }                @Override                public void onCancelled(CancelledException arg0) {                }            });        } catch (Exception e) {            //do something        }    }}

2、工具类：

package com.chen.demo;import android.app.Activity;import android.util.DisplayMetrics;public class Utils {    /**     * 获取屏幕尺寸     *     * @param activity Activity     * @return 屏幕尺寸像素值，下标为0的值为宽，下标为1的值为高     */    public static int[] getScreenSize(Activity activity) {        DisplayMetrics metrics = new DisplayMetrics();        activity.getWindowManager().getDefaultDisplay().getMetrics(metrics);        return new int[]{metrics.widthPixels, metrics.heightPixels};    }    /**     * px转换dp     */    public static int px2dp(Activity activity, int px) {        final float scale = activity.getResources().getDisplayMetrics().density;        return (int) (px / scale + 0.5f);    }    /**     * dp转换px     */    public static int dp2px(Activity activity, int dip) {        final float scale = activity.getResources().getDisplayMetrics().density;        return (int) (dip * scale + 0.5f);    }}

3、主activity

package com.chen.demo;import android.app.Activity;import android.os.Bundle;import android.widget.ListView;import android.widget.TextView;import java.util.ArrayList;public class MainActivity extends Activity {    ListView listView;    ArrayList<PicBean> list;    MyAdapter myAdapter;    TextView screen_width;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        listView= (ListView) findViewById(R.id.listView);        screen_width= (TextView) findViewById(R.id.screen_width);        screen_width.setText("屏幕宽度为==="+Utils.getScreenSize(this)[0]);        list=new ArrayList<PicBean>();        myAdapter=new MyAdapter(list,this);        //假装数据是网络请求，后台拿到的。网上找的一写图片        list.add(new PicBean("http://img1.3lian.com/2015/w7/98/d/22.jpg","1600","900"));        list.add(new PicBean("http://pic2.ooopic.com/11/79/98/31bOOOPICb1_1024.jpg","1024","989"));        list.add(new PicBean("http://qq.yh31.com/tp/ls/201204171232251847.jpg","300","5104"));        list.add(new PicBean("http://img3.3lian.com/2013/s1/74/d/82.jpg","500","682"));        list.add(new PicBean("http://ww3.sinaimg.cn/bmiddle/6d0258b4gw1f71lgzahmaj22p80b4npe.jpg","440","50"));        list.add(new PicBean("http://ww4.sinaimg.cn/square/006iaWqjjw1f8xiqrsp39j30ia0iagmr.jpg","80","80"));        listView.setAdapter(myAdapter);    }}

4、adapter

package com.chen.demo;import android.app.Activity;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.ImageView;import android.widget.RelativeLayout;import android.widget.TextView;import java.util.ArrayList;/** * Created by lenovo on 2016/10/20. */public class MyAdapter extends BaseAdapter {    private ArrayList<PicBean> list=new ArrayList<>();    private Activity act;    public MyAdapter(ArrayList<PicBean> list, Activity act) {        this.list = list;        this.act = act;    }    @Override    public int getCount() {        return list.size();    }    @Override    public Object getItem(int position) {        return list.get(position);    }    @Override    public long getItemId(int position) {        return position;    }    @Override    public View getView(int position, View convertView, ViewGroup parent) {        ViewHolder holder = null;        if (convertView == null) {            holder = new ViewHolder();            convertView = LayoutInflater.from(act).inflate(R.layout.pic_item_layout, null);            holder.img_rl = (RelativeLayout) convertView.findViewById(R.id.img_rl);            holder.img = (ImageView) convertView.findViewById(R.id.img);            holder.long_img_tv= (TextView) convertView.findViewById(R.id.long_img_tv);            holder.src_width_tv= (TextView) convertView.findViewById(R.id.src_width_tv);            holder.src_height_tv= (TextView) convertView.findViewById(R.id.src_height_tv);            holder.src_ratio_tv= (TextView) convertView.findViewById(R.id.src_ratio_tv);            holder.result_width_tv= (TextView) convertView.findViewById(R.id.result_width_tv);            holder.result_height_tv= (TextView) convertView.findViewById(R.id.result_height_tv);            holder.result_ratio_tv= (TextView) convertView.findViewById(R.id.result_ratio_tv);            convertView.setTag(holder);        } else {            holder = (ViewHolder) convertView.getTag();        }        PicBean picBean = list.get(position);        String img_url=picBean.getImgUrl();        String widith = picBean.getWidth();        String height = picBean.getHeight();        //尽可能的把处理交给工具。这样，展示部分代码就简洁了        BitmapHelper.displayImg_Fit_XY(holder.img,img_url,holder.img_rl,holder.long_img_tv,widith,height,act, holder.src_width_tv,holder.src_height_tv,holder.src_ratio_tv,holder.result_width_tv,holder.result_height_tv,holder.result_ratio_tv);        return convertView;    }    class ViewHolder {        RelativeLayout img_rl;        ImageView img;        //显示长图标记的textview        TextView long_img_tv;        //图片原始宽度        TextView src_width_tv;        //图片原始高度        TextView src_height_tv;        //原始宽高的比例        TextView src_ratio_tv;        //图片处理过后的宽度        TextView result_width_tv;        //图片处理过后的高度        TextView result_height_tv;        //图片处理后的宽高的比例        TextView result_ratio_tv;    }}