Android JNI实现锅炉压力显示系统详解

//
// Created by DELL on 2023/8/13.
//
#include <stdio.h>
#include <stdlib.h>
#include <jni.h>
#include <unistd.h>
int pressure = 20;
int getPressure() {
    int increase = rand() % 25;
    pressure += increase;
    return pressure;
}
/**
 * 从锅炉感应器中得到锅炉压力值
 */
jint Java_com_example_guolu_MainActivity_getPressure(JNIEnv *env, jobject thiz) {
    int pressure = getPressure();
    return pressure;
}

plugins {
    id 'com.android.application'
}
android {
    compileSdkVersion 33
    buildToolsVersion "30.0.3"
    defaultConfig {
        applicationId "com.example.guolu"
        minSdkVersion 23
        targetSdkVersion 33
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        // 增加cmake控制属性
        externalNativeBuild {
            cmake {
                // 指定编译架构
                abiFilters 'arm64-v8a', 'armeabi-v7a', 'x86', 'x86_64'
            }
        }
    }
    // 在android节点下
    // 指定CMakeLists.txt路径
    externalNativeBuild {
        cmake {
            // 在该文件种设置所要编写的c源码位置，以及编译后so文件的名字
            path 'CMakeLists.txt'
        }
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}
dependencies {
    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'com.google.android.material:material:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}

public class MainActivity extends AppCompatActivity {
    {
        System.loadLibrary("GuoLu");
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        PressureView pressureView = new PressureView(this);
        setContentView(pressureView);
        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    SystemClock.sleep(1000);
                    int pressure = Math.round(getPressure());//0-250
                    pressureView.setPressure(pressure);
                    if (pressure > 220) {//如果压力大于220就要爆炸
                        break;
                    }
                }
            }
        }).start();
    }
    /**
     * native代码
     * 调用C代码中对应的方法
     *
     * @return
     */
    public native int getPressure();
}

/**
 * @Author: ly
 * @Date: 2023/8/13
 * @Description: 锅炉压力值显示自定义view
 */
public class PressureView extends View {
    /**
     * 锅炉压力值
     */
    private int pressure;
    /**
     * 画笔
     */
    private Paint paint;
    public PressureView(Context context) {
        this(context, null);
    }
    public PressureView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }
    public PressureView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }
    private void init() {
        paint = new Paint();
        paint.setAntiAlias(true);//设置抗锯齿
        paint.setTextSize(20);
    }
    public void setPressure(int pressure) {
        this.pressure = pressure;
//        invalidate(); 在主线程调用
        postInvalidate();//在子线程使用这个进行绘制 onDraw() 执行
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if (pressure > 220) {
            //1.如果压力值大于200，就绘制文本，显示锅炉爆炸了，快跑
            canvas.drawText("快跑！", 10, getHeight() / 2, paint);
        } else {
            //2.正常和提示的情况
            paint.setColor(Color.GRAY);
            canvas.drawRect(10, 10, 60, 260, paint);
            //设置背景颜色为灰色
            //2.1.如果小于200正常显示，并且设置画笔颜色，绿色
            if (pressure < 200) {
                paint.setColor(Color.GREEN);
                canvas.drawRect(10, 260 - pressure, 60, 260, paint);
            }
            //2.2.如果大于200警示显示，并且设置画笔颜色，红色
            if (pressure > 200) {
                paint.setColor(Color.RED);
                canvas.drawRect(10, 260 - pressure, 60, 260, paint);
            }
        }
    }
}