安卓NDK开发案列二：模仿压力表

前言：今天我们通过JNI来模仿一个压力表的变化！

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效果如图所示：

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MainActivity.java:

package com.fly.demo6;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;public class MainActivity extends AppCompatActivity {    MyView pb;    private JNI jni;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        pb = (MyView) findViewById(R.id.pb);        jni = new JNI(pb);    }    public void start(View v) {        new Thread(new Runnable() {            @Override            public void run() {                jni.startMoniter();            }        }).start();    }    public void stop(View v) {        jni.stopMoniter();    }}

JNI.java:

package com.fly.demo6;import static com.fly.demo6.R.id.pb;/** * Created by Fly on 2017/7/6. */public class JNI {    static {        System.loadLibrary("native-lib");    }    MyView pb;    public JNI(MyView pb) {        this.pb = pb;    }    public native void startMoniter();    public native void stopMoniter();    public void setPressure(int pressure) {        //pb.setProgress(pressure);        pb.setPressure(pressure);    }}

MyView.java:

package com.fly.demo6;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.util.AttributeSet;import android.view.View;/** * Created by Fly on 2017/7/16. */public class MyView extends View {    Paint paint;    int pressure = 0;    public MyView(Context context, AttributeSet attrs, int defStyle) {        super(context, attrs, defStyle);        paint = new Paint();    }    public MyView(Context context, AttributeSet attrs) {        super(context, attrs);        paint = new Paint();    }    public MyView(Context context) {        super(context);        paint = new Paint();    }    @Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        if (pressure < 40) {            paint.setColor(Color.GREEN);        } else if (pressure < 80) {            paint.setColor(Color.YELLOW);        } else {            paint.setColor(Color.RED);        }        canvas.drawRect(50, 200 - pressure, 100, 200, paint);        canvas.drawText("当前压力值" + pressure, 50, 50, paint);        paint.setTextSize(25);    }    public void setPressure(int pressure) {        this.pressure = pressure;        //invalidate只能在主线程调用 子线程用postInvalidate()        //invalidate();        postInvalidate();    }}

简单的布局：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    tools:context=".MainActivity">    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:onClick="start"        android:text="开始检测" />    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:onClick="stop"        android:text="停止检测" />    <com.fly.demo6.MyView        android:id="@+id/pb"        android:layout_width="match_parent"        android:layout_height="match_parent" /></LinearLayout>

C代码：

//// Created by Fly on 2017/7/16.//#include <jni.h>#include <stdlib.h>#include <unistd.h>int getPressure() {    return rand() % 100;}int flag = 0;/* * Class:     com_fly_demo6_JNI * Method:    startMoniter * Signature: ()V */JNIEXPORT void JNICALL Java_com_fly_demo6_JNI_startMoniter        (JNIEnv *env, jobject obj) {    flag = 1;    while (flag) {        //①拿到字节码对象        sleep(1);        jclass clazz = (*env)->FindClass(env, "com/fly/demo6/JNI");        jmethodID methodID = (*env)->GetMethodID(env, clazz, "setPressure", "(I)V");        (*env)->CallVoidMethod(env, obj, methodID, getPressure());    }}/* * Class:     com_fly_demo6_JNI * Method:    stopMoniter * Signature: ()V */JNIEXPORT void JNICALL Java_com_fly_demo6_JNI_stopMoniter        (JNIEnv *env, jobject obj) {    flag = 0;}

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