Android：H2-20:水平仪

1. 任务描述

这里介绍的水平仪就是那种比较传统的水平仪，在一个透明的圆盘中充满某种液体，液体中留有一个气泡，当一端翘起时，该气泡将会浮向翘起的一端。

该程序用了一个自定义View，该自定义View很简单，就是绘制透明圆盘和气泡——其中气泡的位置会动态改变。

在真机中测试该程序，可看到下图展示的结果：

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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">
    <com.keven.android.waterlevel.WaterLevel
        android:id="@+id/WaterLevelView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />
</LinearLayout>

WaterLevel.java

package com.keven.android.waterlevel;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.Shader;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.view.Display;
import android.view.View;
import android.view.WindowManager;
import androidx.annotation.Nullable;
public class WaterLevel extends View {
    public Bitmap back;
    public Bitmap bubble;
    private WindowManager windowsMannager;
    private Paint paint;
    public int bubbleX = 0;
    public int bubbleY = 0;
    public WaterLevel(Context context) {
        this(context, null);
    }

    public WaterLevel(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }
    public WaterLevel(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        Settings(context);
        initView();
    }
    private void initView() {
        Display windowDisplay = windowsMannager.getDefaultDisplay();
        DisplayMetrics metrics = new DisplayMetrics();
        windowDisplay.getMetrics(metrics);
        int ScreenWidth = metrics.widthPixels;
        back = Bitmap.createBitmap(ScreenWidth, ScreenWidth, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(back);
        paint = new Paint();
        paint.setAntiAlias(true);
        paint.setStyle(Paint.Style.STROKE);

        LinearGradient linearGradient = new LinearGradient(0f, ScreenWidth, ScreenWidth * 0.8f, ScreenWidth * 0.2f, Color.YELLOW, Color.WHITE, Shader.TileMode.MIRROR);
        // 设置渐变笔刷
        paint.setShader(linearGradient);
        // 绘制圆形
        canvas.drawCircle(ScreenWidth / 2, ScreenWidth / 2, ScreenWidth / 2, paint);
        Paint paint1 = new Paint();
        paint1.setAntiAlias(true);
        paint1.setStrokeWidth(5F);
        paint1.setColor(Color.BLACK);
// 绘制边框
        canvas.drawCircle(ScreenWidth / 2, ScreenWidth / 2, ScreenWidth / 2, paint1);
        //绘制 水平线
        canvas.drawLine(0f, ScreenWidth / 2, ScreenWidth, ScreenWidth / 2, paint1);
        //绘制垂直线
        canvas.drawLine(ScreenWidth / 2, 0f, ScreenWidth / 2, ScreenWidth, paint1);
        paint1.setStrokeWidth(10f);
        paint1.setColor(Color.RED);
//        canvas.drawLine(ScreenWidth/2 - 30  , ScreenWidth/ 2 , ScreenWidth/2+30  , ScreenWidth /2  , paint1 );
//        canvas.drawLine(ScreenWidth/2  , ScreenWidth/ 2- 30  , ScreenWidth/2 , ScreenWidth /2 +30  , paint1 );
        canvas.drawLine(ScreenWidth / 2, 0, ScreenWidth / 2, ScreenWidth, paint1);
        canvas.drawLine(0, ScreenWidth / 2, ScreenWidth, ScreenWidth / 2, paint1);
        bubble = BitmapFactory.decodeResource(getResources(), R.drawable.ball);

    }
    private void Settings(Context context) {
        windowsMannager = (WindowManager) context.getSystemService(
                Context.WINDOW_SERVICE
        );
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        // 绘制表
        canvas.drawBitmap(back, 0, 0, paint);
        canvas.drawBitmap(bubble, bubbleX, bubbleY, paint);
    }
}

MainActivity.java

package com.keven.android.waterlevel;

import androidx.appcompat.app.AppCompatActivity;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity implements SensorEventListener {
    private SensorManager sensorMannager;
    private WaterLevel waterLevelView;
    private int MAX_Angle = 30;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initData();
        initView();
        initEvent();
    }
    private void initData() {
        sensorMannager = (SensorManager) getSystemService(SENSOR_SERVICE);

        sensorMannager.registerListener(this, sensorMannager.getDefaultSensor(Sensor.TYPE_ORIENTATION), SensorManager.SENSOR_DELAY_GAME);

    }

    private void initView() {
        waterLevelView = findViewById(R.id.WaterLevelView);
    }

    private void initEvent() {

    }

    // 注册床传感器回调
    @Override
    public void onSensorChanged(SensorEvent sensorEvent) {
        float[] values = sensorEvent.values;
        int type = sensorEvent.sensor.getType();
        switch (type) {
            case Sensor.TYPE_ORIENTATION:
                float yAngle = values[1];
                float zAngle = values[2];

                int x = (waterLevelView.back.getWidth() - waterLevelView.bubble.getWidth()) / 2;
                int y = (waterLevelView.back.getHeight() - waterLevelView.bubble.getHeight()) / 2;

                if (Math.abs(zAngle) <= MAX_Angle) {
                    int deltax = (int) ((waterLevelView.back.getWidth() - waterLevelView.bubble.getWidth()) / 2 * zAngle / MAX_Angle);
                    x += deltax;
                } else if (zAngle > MAX_Angle) {
                    x = 0;
                } else {
                    x = waterLevelView.back.getWidth() - waterLevelView.bubble.getWidth();
                }

                if (Math.abs(yAngle) < MAX_Angle) {
                    int deltay = (int) ((waterLevelView.back.getHeight() - waterLevelView.bubble.getHeight()) / 2 * yAngle / MAX_Angle);
                    y += deltay;
                } else if (yAngle > MAX_Angle) {
                    y = waterLevelView.back.getHeight() - waterLevelView.bubble.getHeight();
                } else {
                    y = 0;
                }

                if (isContaint(x, y)) {
                    waterLevelView.bubbleX = x;
                    waterLevelView.bubbleY = y;
                    waterLevelView.postInvalidate();
                    break;
                }

        }
    }

    private boolean isContaint(int x, int y) {

        int Cy = y + waterLevelView.bubble.getHeight() / 2;
        int Cx = x + waterLevelView.bubble.getWidth() / 2;

        int Bcy = waterLevelView.back.getHeight() / 2;
        int Bcx = waterLevelView.back.getWidth() / 2;

        double distance = Math.sqrt((Cx - Bcx) * (Cy - Bcy) + (Cy - Bcy) * (Cx - Bcx));

        return distance < (waterLevelView.back.getWidth() - waterLevelView.bubble.getWidth()) / 2;
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int i) {

    }
}