1.在电脑端使用ncnn实现分类(alexnet)

s1，安装g++，cmake，protobuf，opencv

s2，对源码进行编译

git clone https://github.com/Tencent/ncnn
$ cd <ncnn-root-dir>
$ mkdir -p build
$ cd build
$ cmake ..
$ make -j4

s3，准备caffe模型文件(alexnet)

deploy.prototxt 
snapshot_10000.caffemodel 

alexnet deploy.prototxt， caffemodel

s4，使用ncnn转换工具将旧caffe版本的prototxt和caffemodel转新版本

将旧caffe版本的prototxt和caffemodel存放在caffe/build/tools目录下，执行如下命令完成转换

./upgrade_net_proto_text [old prototxt] [new prototxt]
./upgrade_net_proto_binary [old caffemodel] [new caffemodel]

s5，将deploy.prototxt中输入层替换成input层(如果只读取一张图片将dim设置为1)

layer {
  name: "data"
  type: "Input"
  top: "data"
  input_param { shape: { dim: 1 dim: 3 dim: 227 dim: 227 } }
}

s6，使用caffe2ncnn工具将caffe model转成ncnn model

./caffe2ncnn deploy.prototxt bvlc_alexnet.caffemodel alexnet.param alexnet.bin

在ncnn/build/tools目录下生成param和bin文件。

s7，对模型参数进行加密

./ncnn2mem alexnet.param alexnet.bin alexnet.id.h alexnet.mem.h

在ncnn/build/tools目录下生成.param、.bin和.h文件。

alexnet.param 网络的模型参数

alexnet.bin 网络的权重

alexnet.id.h 在预测图片的时候使用到

s8，编写pc端代码(参考https://blog.csdn.net/qq_36982160/article/details/79929869)

#include <stdio.h>
#include <algorithm>
#include <vector>
#include"gesture.id.h"
#include "net.h"
//使用ncnn，传入的参数第一个是你需要预测的数据，第二个参数是各个类别的得分vector，注意传入的是地址，这样才能在这个函数中改变其值
static int detect_squeezenet( float *data, std::vector<float>& cls_scores) {
    //实例化ncnn：Net，注意include "net.h"，不要在意这时候因为找不到net.h文件而include<net.h>报错，后文会介绍正确的打开方式
    ncnn::Net squeezenet;

    //加载二进制文件，也是照写，后面会介绍对应文件应该放的正确位置
    int a=squeezenet.load_param("demo.param");
    int b=squeezenet.load_param_bin("demo.bin");

    //实例化Mat，前三个参数是维度，第四个参数是传入的data，维度的设置根据你自己的数据进行设置，顺序是w、h、c
    ncnn::Mat in = ncnn::Mat(550, 8, 2, data);

    //实例化Extractor
    ncnn::Extractor ex = squeezenet.create_extractor();
    ex.set_light_mode(true);
    //注意把"data"换成你deploy中的数据层名字
    int d= ex.input("data", in);

    ncnn::Mat out;
    //这里是真正的终点，不多说了，只能仰天膜拜nihui大牛，重点是将prob换成你deploy中最后一层的名字
    int c=ex.extract("prob", out);

    //将out中的值转化为我们的cls_scores，这样就可以返回不同类别的得分了
    cls_scores.resize(out.w);
    for (int j=0; j<out.w; j++) {
        cls_scores[j] = out[j];
        }
        return 0;
    }

int main(int argc, char** argv) {
    //注意，这里的argv是之后从终端输入的参数，我这里是数据源的路径,因为我是从两个文件中生成一个总的数据，所以用了argv[1]和argv[2]，你也可以自己根据需求改变
    const char* imagepath1 = argv[1];
    const char* imagepath2=argv[2];

    FILE *fopeni=NULL;
    FILE *fopenq=NULL;

    fopeni=fopen(imagepath1,"r");
    fopenq=fopen(imagepath2,"r");

    //这是我的数据，i和q相当于图片的两个通道
    float i[4400];
    float q[4400];
    float data[8800];

    int count=4400;
    for (int j = 0; j < count; ++j) {
        fscanf(fopeni,"%f",&i[j]);
        fscanf(fopenq,"%f",&q[j]);
    }

    //这是将iq（相当于图片的两个通道的数据）转化为一个一维向量，需要特别注意的是数据维度的顺序
    for (int j = 0; j < 8800; ++j) {
        if (j<4400) {
            data[j]=i[j];
        }
        else{
            data[j]=q[j-4400];
        }
    }

    char a[13]={'A','B','C','F','G','H','I','J','K','L','M','N','O'};

    //注意，这里是调用ncnn的代码
    std::vector<float> cls_scores;  //用来存储最终各类别的得分
    //这个函数的实现在上面，快去看
    detect_squeezenet(data, cls_scores);
    for (int i = 0; i < cls_scores.size(); ++i) {
        printf("%c : %f\n", a[i],cls_scores[i]);
    }

    return 0;
}

代码是最简单的ncnn使用场景，可以根据自己需求加入代码。

s9，编译代码

(1) 编写CMakeLists.txt

在CMakeLists.txt增加如下两行代码

add_executable(demo demo.cpp)
target_link_libraries(demo ncnn)

CMakeLists.txt如下

find_package(OpenCV QUIET COMPONENTS core highgui imgproc imgcodecs)
if(NOT OpenCV_FOUND)
    find_package(OpenCV REQUIRED COMPONENTS core highgui imgproc)
endif()

include_directories(${CMAKE_CURRENT_SOURCE_DIR}/../src)
include_directories(${CMAKE_CURRENT_BINARY_DIR}/../src)

add_executable(squeezenet squeezenet.cpp)

target_link_libraries(squeezenet ncnn ${OpenCV_LIBS})

add_executable(fasterrcnn fasterrcnn.cpp)
target_link_libraries(fasterrcnn ncnn ${OpenCV_LIBS})

add_executable(demo demo.cpp)
target_link_libraries(demo ncnn)

add_subdirectory(ssd)

(2) 在ncnn根目录下CMakeLists.txt中编译examples语句的注释去掉

##############################################

# add_subdirectory(examples)
# add_subdirectory(benchmark)
add_subdirectory(src)
if(NOT ANDROID AND NOT IOS)
add_subdirectory(tools)
endif()

(3)ncnn/build目录下进行编译，生成demo可执行文件

make

s10，执行

将生成的.param和.bin文件复制到ncnn/build/examples目录下，然后终端cd到ncnn/build/examples，执行：

./demo data_path1 data_path2

2. Win x64 (Visual Studio Community 2017)

s1，安装Visual Studio Community 2017

download Visual Studio Community 2017 from https://visualstudio.microsoft.com/vs/community/
install it
Start → Programs → Visual Studio 2017 → Visual Studio Tools → x64 Native Tools Command Prompt for VS 2017

s2，编译protobuf

download protobuf-3.4.0 from https://github.com/google/protobuf/archive/v3.4.0.zip
> cd <protobuf-root-dir>
> mkdir build-vs2017
> cd build-vs2017
> cmake -G"NMake Makefiles" -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=%cd%/install -Dprotobuf_BUILD_TESTS=OFF -Dprotobuf_MSVC_STATIC_RUNTIME=OFF ../cmake
> nmake
> nmake install

s3，编译ncnn库

> cd <ncnn-root-dir>
> mkdir -p build-vs2017
> cd build-vs2017
> cmake -G"NMake Makefiles" -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=%cd%/install -DProtobuf_INCLUDE_DIR=<protobuf-root-dir>/build-vs2017/install/include -DProtobuf_LIBRARIES=<protobuf-root-dir>/build-vs2017/install/lib/libprotobuf.lib -DProtobuf_PROTOC_EXECUTABLE=<protobuf-root-dir>/build-vs2017/install/bin/protoc.exe ..
> nmake
> nmake install

pick build-vs2017/install folder for further usage

3. Android端使用ncnn

参考：

https://blog.csdn.net/qq_33200967/article/details/82421089

https://blog.csdn.net/qq_36982160/article/details/79931741

s1，使用Android Studio安装ndk

1）打开Android Studio，依次点击File->Settings->Appearance&Behavior->System Settings->Android SDK->SDK Tool，选中NDK，点击apply自动下载安装(如果安装成功会在SDK目录下生成ndk-bundle文件夹)；

2）配置ndk的环境变量

• 打开profile

  sudo vim /etc/profile

• 在profile文件末尾添加ndk路径

  export NDK_HOME=sdkroot/ndk-bundle
  PATH=$NDK_HOME:$PATH

• 保存退出，使用source命令使环境变量生效

  source /etc/profile

• 验证ndk是否配置成功

  ndk-build -v

s2，编译ncnn sdk

通过如下命令编译ncnn sdk，会在ncnn/build-android下生成install文件夹，其中包括：include(调用ncnn所需的头文件)和lib(编译得到的ncnn库libncnn.a)

mkdir build-android
cd build-android
cmake -DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK/build/cmake/android.toolchain.cmake \
    -DANDROID_ABI="armeabi-v7a" -DANDROID_ARM_NEON=ON \
    -DANDROID_PLATFORM=android-14 ..
make
make install
make package

参数设置请参考：https://github.com/Tencent/ncnn/wiki/cmake-打包-android-sdk

ANDROID_ABI 是架构名字，"armeabi-v7a" 支持绝大部分手机硬件
ANDROID_ARM_NEON 是否使用 NEON 指令集，设为 ON 支持绝大部分手机硬件
ANDROID_PLATFORM 指定最低系统版本，"android-14" 就是 android-4.0

s3，对源码进行编译

git clone https://github.com/Tencent/ncnn
$ cd <ncnn-root-dir>
$ mkdir -p build
$ cd build
$ cmake ..
$ make -j4

s4，准备caffe模型文件(alexnet)

deploy.prototxt 
snapshot_10000.caffemodel 

alexnet deploy.prototxt， caffemodel

s5，使用ncnn转换工具将旧caffe版本的prototxt和caffemodel转新版本

将旧caffe版本的prototxt和caffemodel存放在caffe/build/tools目录下，执行如下命令完成转换

./upgrade_net_proto_text [old prototxt] [new prototxt]
./upgrade_net_proto_binary [old caffemodel] [new caffemodel]

s6，将deploy.prototxt中输入层替换成input层(如果只读取一张图片将dim设置为1)

layer {
  name: "data"
  type: "Input"
  top: "data"
  input_param { shape: { dim: 1 dim: 3 dim: 227 dim: 227 } }
}

s7，使用caffe2ncnn工具将caffe model转成ncnn model

./caffe2ncnn deploy.prototxt bvlc_alexnet.caffemodel alexnet.param alexnet.bin

在ncnn/build/tools目录下生成param和bin文件。

s8，对模型参数进行加密

./ncnn2mem alexnet.param alexnet.bin alexnet.id.h alexnet.mem.h

在ncnn/build/tools目录下生成.param、.bin和.h文件。

alexnet.param 网络的模型参数

alexnet.bin 网络的权重

alexnet.id.h 在预测图片的时候使用到

s9，开发安卓项目

(1)在Android Studio上创建一个NCNN1，并选择Include C++ support

(2)在main目录下创建assets目录，并将alexnet.param、alexnet.bin、label.txt拷贝其中

(3)将include文件夹和 alexnet.id.h拷贝到cpp目录下

(4)在main目录下创建jniLibs/armeabi-v7a/目录，并将alexnet.id.h 拷贝其中

(5)在cpp文件夹下创建C++文件，用于加载模型和预测图片

#include <android/bitmap.h>
#include <android/log.h>
#include <jni.h>
#include <string>
#include <vector>
// ncnn
#include "include/net.h"
#include "alexnet.id.h"
#include <sys/time.h>
#include <unistd.h>
static ncnn::UnlockedPoolAllocator g_blob_pool_allocator;
static ncnn::PoolAllocator g_workspace_pool_allocator;
static ncnn::Mat ncnn_param;
static ncnn::Mat ncnn_bin;
static ncnn::Net ncnn_net;
extern "C" {
// public native boolean Init(byte[] param, byte[] bin, byte[] words); JNIEXPORT jboolean JNICALL
Java_com_example_ncnn1_NcnnJni_Init(JNIEnv *env, jobject thiz, jbyteArray param, jbyteArray bin) {
    // init param
    {
        int len = env->GetArrayLength(param);
        ncnn_param.create(len, (size_t) 1u);
        env->GetByteArrayRegion(param, 0, len, (jbyte *) ncnn_param); int ret = ncnn_net.load_param((const unsigned char *) ncnn_param);
        __android_log_print(ANDROID_LOG_DEBUG, "NcnnJni", "load_param %d %d", ret, len);
    }

    // init bin
    {
        int len = env->GetArrayLength(bin);
        ncnn_bin.create(len, (size_t) 1u);
        env->GetByteArrayRegion(bin, 0, len, (jbyte *) ncnn_bin);
        int ret = ncnn_net.load_model((const unsigned char *) ncnn_bin);
        __android_log_print(ANDROID_LOG_DEBUG, "NcnnJni", "load_model %d %d", ret, len);
    }

    ncnn::Option opt;
    opt.lightmode = true;
    opt.num_threads = 4;
    opt.blob_allocator = &g_blob_pool_allocator;
    opt.workspace_allocator = &g_workspace_pool_allocator;

    ncnn::set_default_option(opt);

    return JNI_TRUE;
}

// public native String Detect(Bitmap bitmap);
JNIEXPORT jfloatArray JNICALL Java_com_example_ncnn1_NcnnJni_Detect(JNIEnv* env, jobject thiz, jobject bitmap)
{
    // ncnn from bitmap
    ncnn::Mat in;
    {
        AndroidBitmapInfo info;
        AndroidBitmap_getInfo(env, bitmap, &info);
        int width = info.width; int height = info.height;
        if (info.format != ANDROID_BITMAP_FORMAT_RGBA_8888)
            return NULL;

        void* indata;
        AndroidBitmap_lockPixels(env, bitmap, &indata);
        // 把像素转换成data，并指定通道顺序
        in = ncnn::Mat::from_pixels((const unsigned char*)indata, ncnn::Mat::PIXEL_RGBA2BGR, width, height);
        AndroidBitmap_unlockPixels(env, bitmap);
    }

    // ncnn_net
    std::vector<float> cls_scores;
    {
        // 减去均值和乘上比例
        const float mean_vals[3] = {103.94f, 116.78f, 123.68f};
        const float scale[3] = {0.017f, 0.017f, 0.017f};

        in.substract_mean_normalize(mean_vals, scale);

        ncnn::Extractor ex = ncnn_net.create_extractor();
        // 如果时不加密是使用ex.input("data", in);
        ex.input(mobilenet_v2_param_id::BLOB_data, in);

        ncnn::Mat out;
        // 如果时不加密是使用ex.extract("prob", out);
        ex.extract(mobilenet_v2_param_id::BLOB_prob, out);

        int output_size = out.w;
        jfloat *output[output_size];
        for (int j = 0; j < out.w; j++) {
            output[j] = &out[j];
        }

        jfloatArray jOutputData = env->NewFloatArray(output_size);
        if (jOutputData == nullptr) return nullptr;

        env->SetFloatArrayRegion(jOutputData, 0, output_size, reinterpret_cast<const jfloat *>(*output)); // copy
        return jOutputData;
    }
}
}

(6)在项目包com.example.ncnn1下，修改MainActivity.java中的代码

package com.example.ncnn1;
import android.Manifest;
import android.app.Activity;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.content.res.AssetManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.text.method.ScrollingMovementMethod;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import com.bumptech.glide.Glide;
import com.bumptech.glide.load.engine.DiskCacheStrategy;
import com.bumptech.glide.request.RequestOptions;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class MainActivity extends Activity {
    private static final String TAG = MainActivity.class.getName();
    private static final int USE_PHOTO = 1001;
    private String camera_image_path;
    private ImageView show_image;
    private TextView result_text;
    private boolean load_result = false; private int[] ddims = {1, 3, 224, 224};
    private int model_index = 1;
    private List<String> resultLabel = new ArrayList<>();
    private NcnnJni squeezencnn = new NcnnJni();

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

        try {
            initSqueezeNcnn();
        } catch (IOException e) {
            Log.e("MainActivity", "initSqueezeNcnn error");
        }

        init_view();
        readCacheLabelFromLocalFile();
    }

    private void initSqueezeNcnn() throws IOException {
        byte[] param = null;
        byte[] bin = null;

        {
            InputStream assetsInputStream = getAssets().open("mobilenet_v2.param.bin");
            int available = assetsInputStream.available();
            param = new byte[available];
            int byteCode = assetsInputStream.read(param);
            assetsInputStream.close();
        }

        {
            InputStream assetsInputStream = getAssets().open("mobilenet_v2.bin");
            int available = assetsInputStream.available();
            bin = new byte[available];
            int byteCode = assetsInputStream.read(bin);
            assetsInputStream.close();
        }

        load_result = squeezencnn.Init(param, bin);
        Log.d("load model", "result:" + load_result);
    }

    // initialize view
    private void init_view() {
        request_permissions();
        show_image = (ImageView) findViewById(R.id.show_image);
        result_text = (TextView) findViewById(R.id.result_text);
        result_text.setMovementMethod(ScrollingMovementMethod.getInstance());
        Button use_photo = (Button) findViewById(R.id.use_photo);

        // use photo click
        use_photo.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (!load_result) {
                    Toast.makeText(MainActivity.this, "never load model", Toast.LENGTH_SHORT).show();
                    return;
                }
                PhotoUtil.use_photo(MainActivity.this, USE_PHOTO);
            }
        });
    }

    // load label's name
    private void readCacheLabelFromLocalFile() {
        try {
            AssetManager assetManager = getApplicationContext().getAssets();
            BufferedReader reader = new BufferedReader(new InputStreamReader(assetManager.open("synset.txt")));
            String readLine = null;
            while ((readLine = reader.readLine()) != null) {
                resultLabel.add(readLine);
            }
            reader.close();
        } catch (Exception e) {
            Log.e("labelCache", "error " + e);
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        String image_path;
        RequestOptions options = new RequestOptions().skipMemoryCache(true).diskCacheStrategy(DiskCacheStrategy.NONE);
        if (resultCode == Activity.RESULT_OK) {
            switch (requestCode) {
                case USE_PHOTO:
                    if (data == null) {
                        Log.w(TAG, "user photo data is null");
                        return;
                    }
                    Uri image_uri = data.getData();
                    Glide.with(MainActivity.this).load(image_uri).apply(options).into(show_image);
                    // get image path from uri
                    image_path = PhotoUtil.get_path_from_URI(MainActivity.this, image_uri);
                    // predict image
                    predict_image(image_path);
                    break;
            }
        }
    }

    //  predict image
    private void predict_image(String image_path) {
        // picture to float array
        Bitmap bmp = PhotoUtil.getScaleBitmap(image_path);
        Bitmap rgba = bmp.copy(Bitmap.Config.ARGB_8888, true);

        // resize to 227x227
        Bitmap input_bmp = Bitmap.createScaledBitmap(rgba, ddims[2], ddims[3], false);
        try {
            // Data format conversion takes too long
            // Log.d("inputData", Arrays.toString(inputData));
            long start = System.currentTimeMillis();
            // get predict result
            float[] result = squeezencnn.Detect(input_bmp);
            long end = System.currentTimeMillis();
            Log.d(TAG, "origin predict result:" + Arrays.toString(result));
            long time = end - start; Log.d("result length", String.valueOf(result.length));
            // show predict result and time
            int r = get_max_result(result);
            String show_text = "result：" + r + "\nname：" + resultLabel.get(r) + "\nprobability：" + result[r] + "\ntime：" + time + "ms";
            result_text.setText(show_text);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // get max probability label
    private int get_max_result(float[] result) {
        float probability = result[0];
        int r = 0;
        for (int i = 0; i < result.length; i++) {
            if (probability < result[i]) {
                probability = result[i];
                r = i;
            }
        }
        return r;
    }

    // request permissions
    private void request_permissions() {
        List<String> permissionList = new ArrayList<>();
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
            permissionList.add(Manifest.permission.CAMERA);
        }

        if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            permissionList.add(Manifest.permission.WRITE_EXTERNAL_STORAGE);
        }

        if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            permissionList.add(Manifest.permission.READ_EXTERNAL_STORAGE);
        }

        // if list is not empty will request permissions
        if (!permissionList.isEmpty()) {
            ActivityCompat.requestPermissions(this, permissionList.toArray(new String[permissionList.size()]), 1);
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        switch (requestCode) {
            case 1:
                if (grantResults.length > 0) {
                    for (int i = 0; i < grantResults.length; i++) {
                        int grantResult = grantResults[i];
                        if (grantResult == PackageManager.PERMISSION_DENIED) {
                            String s = permissions[i];
                            Toast.makeText(this, s + " permission was denied", Toast.LENGTH_SHORT).show();
                        }
                    }
                }
                break;
        }
    }
}

(7)在项目的包com.example.ncnn1下，创建一个NcnnJni.java类，用于提供JNI接口，代码如下：

package com.example.ncnn1;

import android.graphics.Bitmap;

public class NcnnJni {
    public native boolean Init(byte[] param, byte[] bin);
    public native float[] Detect(Bitmap bitmap);

    static {
        System.loadLibrary("ncnn_jni");
    }
}

(8)在项目的包com.example.ncnn1下，创建一个PhotoUtil.java类，这个是图片的工具类，代码如下：

package com.example.ncnn1;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.provider.MediaStore;
import java.nio.FloatBuffer;

public class PhotoUtil {
    // get picture in photo
    public static void use_photo(Activity activity, int requestCode) {
        Intent intent = new Intent(Intent.ACTION_PICK);
        intent.setType("image/*");
        activity.startActivityForResult(intent, requestCode);
    }

    // get photo from Uri
    public static String get_path_from_URI(Context context, Uri uri) {
        String result;
        Cursor cursor = context.getContentResolver().query(uri, null, null, null, null);
        if (cursor == null) {
            result = uri.getPath();
        } else {
            cursor.moveToFirst();
            int idx = cursor.getColumnIndex(MediaStore.Images.ImageColumns.DATA);
            result = cursor.getString(idx);
            cursor.close();
        }
        return result;
    }

    // compress picture
    public static Bitmap getScaleBitmap(String filePath) {
        BitmapFactory.Options opt = new BitmapFactory.Options();
        opt.inJustDecodeBounds = true;
        BitmapFactory.decodeFile(filePath, opt);

        int bmpWidth = opt.outWidth;
        int bmpHeight = opt.outHeight;

        int maxSize = 500;

        // compress picture with inSampleSize
        opt.inSampleSize = 1;
        while (true) {
            if (bmpWidth / opt.inSampleSize < maxSize || bmpHeight / opt.inSampleSize < maxSize) {
                break;
            }
            opt.inSampleSize *= 2;
        }
        opt.inJustDecodeBounds = false;
        return BitmapFactory.decodeFile(filePath, opt);
    }
}

(9)修改启动页面的布局，修改如下：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <LinearLayout
        android:id="@+id/btn_ll"
        android:layout_alignParentBottom="true"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/use_photo"
            android:layout_weight="1"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:text="相册" />

    </LinearLayout>

    <TextView
        android:layout_above="@id/btn_ll"
        android:id="@+id/result_text"
        android:textSize="16sp"
        android:layout_width="match_parent"
        android:hint="预测结果会在这里显示"
        android:layout_height="100dp" />
    <ImageView
        android:layout_alignParentTop="true"
        android:layout_above="@id/result_text"
        android:id="@+id/show_image"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</RelativeLayout>

(10)修改APP目录下的CMakeLists.txt文件，修改如下：

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.4.1)

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.
set(ncnn_lib ${CMAKE_SOURCE_DIR}/src/main/jniLibs/armeabi-v7a/libncnn.a)
add_library (ncnn_lib STATIC IMPORTED)
set_target_properties(ncnn_lib PROPERTIES IMPORTED_LOCATION ${ncnn_lib})

add_library( # Sets the name of the library.
            ncnn_jni
            # Sets the library as a shared library.
            SHARED

            # Provides a relative path to your source file(s).
            src/main/cpp/ncnn_jni.cpp )

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

find_library( # Sets the name of the path variable.
                log-lib

                # Specifies the name of the NDK library that
                # you want CMake to locate.
                log )

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( # Specifies the target library.
                        ncnn_jni
                        ncnn_lib
                        jnigraphics

                        # Links the target library to the log library
                        # included in the NDK.
                        ${log-lib} )

(11)修改APP目录下的build.gradle文件，修改如下：

apply plugin: 'com.android.application'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.example.ncnn1"
        minSdkVersion 21
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags "-std=c++11 -fopenmp"
                abiFilters "armeabi-v7a"
            }
        }
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }

    sourceSets {
        main {
            jniLibs.srcDirs = ["src/main/jniLibs"]
            jni.srcDirs = ['src/cpp']
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:28.0.0-rc02'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    testImplementation 'junit:junit:4.12'
    implementation 'com.github.bumptech.glide:glide:4.3.1'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}

(12)最后在配置文件中添加权限

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

(13)编译完成

4. 最后