Android加载大图不OOM

  首先,我们试着往sdcard里放一张400k的图片,但是分辨率是2560*1600

  布局简单

 

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.dell.myapplication.MainActivity">


    <Button

        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="loading ima"
        android:id="@+id/button"

        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"/>

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/imageView"
        android:layout_below="@+id/button"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="213dp"/>
</RelativeLayout>

 

 

  MainActivity

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {
    Button mbutton;
    ImageView mImageView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mbutton= (Button) findViewById(R.id.button);
        mImageView= (ImageView) findViewById(R.id.imageView);
        mbutton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
            Bitmap bitmap= BitmapFactory.decodeFile("/storage/sdcard/test.JPG");//将图片转换为bitmap
                mImageView.setImageBitmap(bitmap);
            }
        });
    }
}

  很简单,设置点击按钮开始加载图片

 

  结果:

 

 

  报的错误:

    08-16 21:17:08.410 2947-2947/com.example.dell.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
                java.lang.OutOfMemoryError
                at android.graphics.BitmapFactory.nativeDecodeStream(Native Method)
              at android.graphics.BitmapFactory.decodeStream(BitmapFactory.java:530)
                at android.graphics.BitmapFactory.decodeFile(BitmapFactory.java:303)
                at android.graphics.BitmapFactory.decodeFile(BitmapFactory.java:329)
                at com.example.dell.myapplication.MainActivity$1.onClick(MainActivity.java:23)
                at android.view.View.performClick(View.java:4240)
                at android.view.View$PerformClick.run(View.java:17721)
                at android.os.Handler.handleCallback(Handler.java:730)
                at android.os.Handler.dispatchMessage(Handler.java:92)
                at android.os.Looper.loop(Looper.java:137)
                at android.app.ActivityThread.main(ActivityThread.java:5103)
                at java.lang.reflect.Method.invokeNative(Native Method)
                at java.lang.reflect.Method.invoke(Method.java:525)
                at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
                at dalvik.system.NativeStart.main(Native Method)

 

  这时候,你可能会想,天呐,我的图片明明只有400Kb啊,怎么可能会OutOfMemoryError!!是我的虚拟机太腊鸡了吗?

 

  其实不是这样

  在Android下采用ARGB来表示颜色  每个像素占4byte。
 
  那么这张图片在Android虚拟机中实际占用内存:2560*1600*4byte=15.6M而我们的虚拟机创建时,Dalvik默认堆得大小是16M,所以这时基本就OOM了。(因为堆上还  有别的东西)
 
  这时候就要对我们的图片进行缩放
 
  那么,如何缩放?当然是根据分辨率缩放。我们将图片和我们的虚拟机进行对比
 
  图片:2560*1600
  手机:320*480
 
  宽缩放: 8
  高缩放: 3
 
  按照大的比例来缩放,这样缩放后的尺寸肯定宽高都小于等于手机的尺寸。
 
  具体方法:
  1 得到图片的分辨率
  2 得到手机的分辨率
  3缩放
 
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {
    Button mbutton;
    ImageView mImageView;
    int screenWidth;
    int screenHeight;

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

        WindowManager wm= (WindowManager) getSystemService(WINDOW_SERVICE);
       screenWidth= wm.getDefaultDisplay().getWidth();
        screenHeight=wm.getDefaultDisplay().getHeight();
    System.out.print("手机宽"+screenWidth+"手机高"+screenHeight);

        mbutton= (Button) findViewById(R.id.button);
        mImageView= (ImageView) findViewById(R.id.imageView);
        mbutton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //创建bitmap工厂的配置参数
                BitmapFactory.Options options=new BitmapFactory.Options();
                //返回null,不去真正解析位图,只是得到宽高等信息
                options.inJustDecodeBounds=true;
               BitmapFactory.decodeFile("/storage/sdcard/test.JPG",options);
                int imgWidth=options.outWidth;
                int imgHeight=options.outHeight;
                System.out.print("图片宽"+imgWidth+"图片高"+imgHeight);

               // 计算缩放比
                int scale=1;
                int scalex=imgWidth/screenWidth;
                int scaley=imgHeight/screenHeight;
                scale=scalex>scaley?scalex:scaley;
                //按照缩放比显示图片
                options.inSampleSize=scale;
                //开始真正解析位图
                options.inJustDecodeBounds=false;
                Bitmap bitmap=BitmapFactory.decodeFile("/storage/sdcard/test.JPG",options);
                mImageView.setImageBitmap(bitmap);
            }
        });
    }
}

 

  结果:

 

  打印结果:

  08-16 22:03:22.542 9790-9790/com.example.dell.myapplication I/System.out: 手机宽320手机高480
  08-16 22:03:38.432 9790-9790/com.example.dell.myapplication I/System.out: 图片宽2560图片高1600

 

posted @ 2016-08-17 10:05  zerocoin  阅读(3576)  评论(0编辑  收藏  举报