在一定范圍裡，按比例縮放圖片，優化展示效果

在listview中，每個條目有一張圖片，圖片的大小是隨機的，怎麼展示才能美觀。很多人用的方法是，在ImageView中，加屬性

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

用來限定ImageView的最大值和最小值。但是，這樣展示的圖片，很多時候會很丑。怎麼才能像微信一樣，有個范圍，超過那個范圍，就壓縮，而且是按比例壓縮。使得展示的很美觀呢？
我不知道微信怎麼寫的，但是盡可能的模仿了。我們項目用的是xUtils3，我這裡針對xUtils3寫。其他理論上類似

效果圖：

說明：
這裡是模仿了微信的展示效果。寬或者高的最大值，不超過屏幕寬度值的一半。我自己設定了寬或者高的最小值，不小於屏幕寬度值的1/6。如上圖的寶劍圖。高是寬的17倍之多，但是高顯示的最大值是屏幕寬的一半，如果此時寬還是它的17分之一，就沒法看了。再比如最下面的貓圖。寬高僅僅80像素。很小，如果按照原先的展示，也沒法看

代碼：
1、核心代碼：處理及展示的工具類：

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 {
            //寬高的計算結果
            final int width_result;
            final int height_result;
            //原始的寬高值
            final int width_src;
            final int height_src;

            int width = Integer.parseInt(w);
            width_src = width;
            int height = Integer.parseInt(h);
            height_src = height;


            //圖片寬或者高的最大值。以屏幕一半為例。
            int halfScreenSize = Utils.getScreenSize(act)[0] / 2;
            //最小值。避免圖片過小
            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);

            //寬高的比例
            float ratio = 0;

            if (width > halfScreenSize || height > halfScreenSize) {

                //需要限制大小
                if (width > height) {
                    //橫圖。得到寬高比例
                    ratio = 1.0f * height / width;

                    if (width > halfScreenSize) {
                        width = halfScreenSize;
                    }
                    height = (int) (width * ratio);
                    if (height < minSize) {
                        height = minSize;
                    }

                } else if (height >= width) {
                    //豎圖
                    ratio = 1.0f * width / height;
                    if (height > halfScreenSize) {
                        height = halfScreenSize;
                    }
                    width = (int) (height * ratio);
                    if (width < minSize) {
                        width = minSize;
                    }

                }

            } else {

                //長和寬都沒有超過屏幕的一半
                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("原寬=" + 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("結果寬=" + width_result);
            result_height_tv.setText("結果高=" + height_result);
            if (width_result > height_result) {
                result_ratio_tv.setText("結果-width / height=" + (1.0f * width_result / height_result));
            } else {
                result_ratio_tv.setText("結果-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() {
                @Override
                public void onSuccess(Drawable arg0) {

                    //寬是高的3倍，或者高是寬的3倍。就視為長圖
                    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、工具類：

package com.chen.demo;

import android.app.Activity;
import android.util.DisplayMetrics;


public class Utils {

    /**
     * 獲取屏幕尺寸
     *
     * @param activity Activity
     * @return 屏幕尺寸像素值，下標為0的值為寬，下標為1的值為高
     */
    public static int[] getScreenSize(Activity activity) {
        DisplayMetrics metrics = new DisplayMetrics();
        activity.getWindowManager().getDefaultDisplay().getMetrics(metrics);
        return new int[]{metrics.widthPixels, metrics.heightPixels};
    }

    /**
     * px轉換dp
     */
    public static int px2dp(Activity activity, int px) {
        final float scale = activity.getResources().getDisplayMetrics().density;
        return (int) (px / scale + 0.5f);
    }

    /**
     * dp轉換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 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("屏幕寬度為==="+Utils.getScreenSize(this)[0]);

        list=new ArrayList();
        myAdapter=new MyAdapter(list,this);


        //假裝數據是網絡請求，後台拿到的。網上找的一寫圖片
        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 list=new ArrayList<>();
    private Activity act;

    public MyAdapter(ArrayList 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();

        //盡可能的把處理交給工具。這樣，展示部分代碼就簡潔了
        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;
        //顯示長圖標記的textview
        TextView long_img_tv;
        //圖片原始寬度
        TextView src_width_tv;
        //圖片原始高度
        TextView src_height_tv;
        //原始寬高的比例
        TextView src_ratio_tv;
        //圖片處理過後的寬度
        TextView result_width_tv;
        //圖片處理過後的高度
        TextView result_height_tv;
        //圖片處理後的寬高的比例
        TextView result_ratio_tv;
    }
}