android中加载大图片到内存

在android中，要明确一点，图片占用的内存大小与图片的实际大小无关，只与图片的分辨率有关，图片占用的内存空间为  图片分辨率 （高*宽）*4byte。

布局文件 

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              xmlns:tools="http://schemas.android.com/tools"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:orientation="vertical"
              tools:context=".MainActivity">

    <Button
        android:id="@+id/bt"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="加载大图片"/>

    <ImageView
        android:id="@+id/iv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</LinearLayout>

实现代码 

package cn.test.ning.imagedemo;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.view.View;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends Activity {
    private ImageView iv;
    private Button bt;

    private int screenWidth;
    private int screenHight;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_bigimage);

        //获取屏幕信息
        WindowManager windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
        //获取屏幕宽度
        screenWidth = windowManager.getDefaultDisplay().getWidth();
        //获取屏幕高度
        screenHight = windowManager.getDefaultDisplay().getHeight();

        iv = (ImageView) this.findViewById(R.id.iv);
        // Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher);
        // iv.setImageBitmap(bitmap);

        bt = (Button) this.findViewById(R.id.bt);


        bt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
               // Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.very_large_photo);

                BitmapFactory.Options opts = new BitmapFactory.Options();
                //不真实的解析位图，只是返回位图的相关信息
                opts.inJustDecodeBounds = true;
                Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.very_large_photo,opts);
                int width = opts.outWidth;//图片的宽度
                int higth = opts.outHeight;//图片的高度

                //计算缩放比
                int scale = 1;
                int scaleX = width /screenWidth;
                int scaleY = higth /screenHight;
                scale = (scaleX>scaleY?scaleX:scaleY);
                if (scale<1){
                    scale = 1;
                }
                //设置图片的缩放比
                opts.inSampleSize = scale;
                //真实解析位图
                opts.inJustDecodeBounds = false;
                //加载图片 重要的步骤
                bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.very_large_photo,opts);
                iv.setImageBitmap(bitmap);
            }
        });

    }

}

使用到的图片