Android JNI实现锅炉压力显示系统详解

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第一步创建GuoLu.c文件

//
// 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;
}

第二步在build.gradle文件中，进行相关配置

plugins {id 'com.android.application'
}android {compileSdkVersion 33buildToolsVersion "30.0.3"defaultConfig {applicationId "com.example.guolu"minSdkVersion 23targetSdkVersion 33versionCode 1versionName "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 falseproguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'}}compileOptions {sourceCompatibility JavaVersion.VERSION_1_8targetCompatibility 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'
}

第三步实现在MainActivity中，调用相关的C代码，显示锅炉压力值，根据压力值显示不同的UI在Android设备上

public class MainActivity extends AppCompatActivity {{System.loadLibrary("GuoLu");}@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);PressureView pressureView = new PressureView(this);setContentView(pressureView);new Thread(new Runnable() {@Overridepublic void run() {while (true) {SystemClock.sleep(1000);int pressure = Math.round(getPressure());//0-250pressureView.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();
}

第四步实现自定义View，PressureView

/*** @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}@Overrideprotected 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);}}}
}