listview的条目上的图片按照宽高比例进行缩放设置

 

   

package com.itheima.googleplay2.view;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.widget.ImageView;
public class SubjectImageView extends ImageView {
    public SubjectImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        // TODO Auto-generated constructor stub
    }
    
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
 //获取真实的图片
        Drawable drawable = getDrawable();
        
        if(drawable!=null){
            //获取真实的宽
            int width = drawable.getMinimumWidth();
            //获取真实的高 
            int height = drawable.getMinimumHeight();
            //计算宽和高的比例 
            float scale = (float)width/height;
            //获取测量宽的规则
            int withsize = MeasureSpec.getSize(widthMeasureSpec);
            //按照比例计算高的测量规则 
            int heightsize = (int) (withsize/scale);
            //设置高的测量规则 第一个值是按照比例计算的高 第二个参数是测量模式 精确
            heightMeasureSpec = MeasureSpec.makeMeasureSpec(heightsize, MeasureSpec.EXACTLY);
            
        }
        
        
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }