Android位图(图片)加载引入的内存溢出问题详细解析

package com.itbird.BitmapOOM;

import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.widget.ImageView;

import androidx.appcompat.app.AppCompatActivity;

import com.itbird.R;

public class ImageViewLoadBitmapTestActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.imageviewl_load_bitmap_test);
        ImageView imageView =  findViewById(R.id.imageview);
        imageView.setImageResource(R.drawable.bigpic);
        imageView.setBackgroundResource(R.drawable.bigpic);
        imageView.setImageBitmap(BitmapFactory.decodeFile("path/big.jpg"));
        imageView.setImageBitmap(BitmapFactory.decodeResource(getResources(), R.drawable.bigpic));
    }
}

public final class Bitmap implements Parcelable {
    private static final String TAG = "Bitmap";
     ...
    private byte[] mBuffer;
     ...
    }

public final class Bitmap implements Parcelable {
    ...
    // Convenience for JNI access
    private final long mNativePtr;
    ...
 }

 /**
     * 以最省内存的方式读取本地资源的图片
     */
    public static Bitmap readBitMap(String path, BitmapFactory.Options opt, InputStream is) {
        opt.inPreferredConfig = Bitmap.Config.RGB_565;
        if (Build.VERSION.SDK_INT <=android.os.Build.VERSION_CODES.KITKAT ) {
            opt.inPurgeable = true;
            opt.inInputShareable = true;
        }
        opt.inSampleSize = 2;//二分之一缩放，可写1即100%显示
        //获取资源图片
        try {
            is = new FileInputStream(path);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        return BitmapFactory.decodeStream(is, null, opt);
    }

Bitmap(long nativeBitmap, int width, int height, int density,
        boolean isMutable, boolean requestPremultiplied,
        byte[] ninePatchChunk, NinePatch.InsetStruct ninePatchInsets) {
    ...
    mNativePtr = nativeBitmap;
    long nativeSize = NATIVE_ALLOCATION_SIZE + getAllocationByteCount();
    <!--辅助回收native内存-->
    NativeAllocationRegistry registry = new NativeAllocationRegistry(
        Bitmap.class.getClassLoader(), nativeGetNativeFinalizer(), nativeSize);
    registry.registerNativeAllocation(this, nativeBitmap);
   if (ResourcesImpl.TRACE_FOR_DETAILED_PRELOAD) {
        sPreloadTracingNumInstantiatedBitmaps++;
        sPreloadTracingTotalBitmapsSize += nativeSize;
    }
}

    /**
     * 以计算的压缩比例加载大图片
     *
     * @param res
     * @param resId
     * @param reqWidth
     * @param reqHeight
     * @return
     */
    public static Bitmap decodeCalSampledBitmapFromResource(Resources res, int resId, int reqWidth, int reqHeight) {
        // 检查bitmap的大小
        final BitmapFactory.Options options = new BitmapFactory.Options();
        // 设置为true，BitmapFactory会解析图片的原始宽高信息，并不会加载图片
        options.inJustDecodeBounds = true;
        options.inPreferredConfig = Bitmap.Config.RGB_565;

        BitmapFactory.decodeResource(res, resId, options);

        // 计算采样率
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

        // 设置为false，加载bitmap
        options.inJustDecodeBounds = false;

        return BitmapFactory.decodeResource(res, resId, options);
    }

    /*********************************
     * @function: 计算出合适的图片倍率
     * @options: 图片bitmapFactory选项
     * @reqWidth: 需要的图片宽
     * @reqHeight: 需要的图片长
     * @return: 成功返回倍率, 异常-1
     ********************************/
    private static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth,
                                             int reqHeight) {
        // 设置初始压缩率为1
        int inSampleSize = 1;
        try {
            // 获取原图片长宽
            int width = options.outWidth;
            int height = options.outHeight;
            // reqWidth/width,reqHeight/height两者中最大值作为压缩比
            int w_size = width / reqWidth;
            int h_size = height / reqHeight;
            inSampleSize = w_size > h_size ? w_size : h_size;  // 取w_size和h_size两者中最大值作为压缩比
            Log.e("inSampleSize", String.valueOf(inSampleSize));
        } catch (Exception e) {
            return -1;
        }
        return inSampleSize;
    }

 /**
     * 回收bitmap
     */
    private static void recycleBitmap(ImageView iv) {
        if (iv != null && iv.getDrawable() != null) {
            BitmapDrawable bitmapDrawable = (BitmapDrawable) iv.getDrawable();
            iv.setImageDrawable(null);
            if (bitmapDrawable != null) {
                Bitmap bitmap = bitmapDrawable.getBitmap();
                if (bitmap != null) {
                    bitmap.recycle();
                }
            }
        }
    }

    /**
     * 在Activity或Fragment的onDestory方法中进行回收(必须确保bitmap不在使用)
     */
    public static void recycleBitmap(Bitmap bitmap) {
        // 先判断是否已经回收
        if (bitmap != null && !bitmap.isRecycled()) {
            // 回收并且置为null
            bitmap.recycle();
            bitmap = null;
        }
    }