package com.itheima.monitor;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.ProgressBar;
public class MainActivity extends Activity {
    private MyProgressBar pb;
    static{
        System.loadLibrary("hello");
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        pb = (MyProgressBar) findViewById(R.id.pb);//自定义进度条
        pb.setMax(100);
    }
   public void start(View v){
       new Thread(){
           public void run() {
               startMonitor();
           };
       }.start();
   }
   public void stop(View v){
       stopMonitor();
   }
    
   public native void startMonitor();
   public native void stopMonitor();
   
   public void show(int pressure){
       pb.setPressure(pressure);
   }
}

package com.itheima.monitor;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

/*界面：
<com.itheima.monitor.MyProgressBar
android:id="@+id/pb"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
/>*/

public class MyProgressBar extends View {

    private int pressure;
    private int max;
    public MyProgressBar(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public MyProgressBar(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public MyProgressBar(Context context) {
        super(context);
    }

    public void setPressure(int pressure) {
        this.pressure = pressure;
        //使当前组件MyProgressBar视图无效，如果当前视图是可见的，那么onDraw会调用，只能在主线程使用
//        invalidate();  主线程调用这个方法
        postInvalidate();//子线城用这个方法，这样进度条才会一直绘制进度条。
        
    }
    public void setMax(int max) {
        this.max = max;
    }
    
    //在自定义组件绘制内容
    @Override
    protected void onDraw(Canvas canvas) {
        //任何组件在显示在页面上的时候onDraw方法都会调用一次，
        Paint paint = new Paint();//画笔
        if(pressure < 50){
            paint.setColor(Color.GREEN);
        }
        else if(pressure < 80){
            paint.setColor(0xffff8800);
        }
        else {
            paint.setColor(Color.RED);
        }
        canvas.drawRect(10, 10 + max - pressure, 30, 10 + max, paint);//画矩形,也就是画进度条。
        canvas.drawText("dddd", 10, 10, paint);//写文字
    }
}

#include <jni.h>
#include <stdio.h>
#include <stdlib.h>

int getPressure(){
    //……监测电压……运算得到压力值
    return rand() % 101;
}

int monitor;
JNIEXPORT void JNICALL Java_com_itheima_monitor_MainActivity_startMonitor
  (JNIEnv * env, jobject obj){//obj是MainActivity，
    monitor = 1;
    while(monitor){
        //获取锅炉压力
        int pressure = getPressure();

//C中通过反射调用java的方法

        //jclass  (*FindClass)(JNIEnv*, const char*);
        jclass clazz = (*env)->FindClass(env, "com/itheima/monitor/MainActivity");
        //jmethodID  (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);
        jmethodID methodId = (*env)->GetMethodID(env, clazz, "show", "(I)V");//(I)V是方法的签名，返回值是void参数是int
        //void  (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);
        (*env)->CallVoidMethod(env, obj, methodId, pressure);//调用java的show方法
        sleep(1);
    }

}


JNIEXPORT void JNICALL Java_com_itheima_monitor_MainActivity_stopMonitor
 (JNIEnv * env, jobject obj){
    monitor = 0;
}

//进入工程的bin\classes目录，执行javap -s Mainactivity的全包名类名，就可以查看MainActivity的所有方法的签名。