Android onDraw 画表盘实现
1. 简介
在Android上实现画表盘的功能，可以通过自定义View并重写onDraw方法来实现。本文将详细介绍整个实现过程，并提供相应的代码示例和注释。
2. 实现步骤
下面是画表盘的实现步骤：
| 步骤 | 描述 |
|---|---|
| 步骤1 | 创建自定义View类，继承自View |
| 步骤2 | 重写onMeasure方法，设置View的大小 |
| 步骤3 | 重写onDraw方法，绘制表盘 |
| 步骤4 | 在Activity中使用自定义View |
下面将详细介绍每个步骤的具体实现。
步骤1：创建自定义View类
public class DialView extends View {
// 构造方法
public DialView(Context context) {
super(context);
}
}
步骤2：重写onMeasure方法
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// 设置View的大小
int desiredWidth = 200; // 设置宽度
int desiredHeight = 200; // 设置高度
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
// 根据测量模式，设置宽高
int width;
int height;
if (widthMode == MeasureSpec.EXACTLY) {
width = widthSize;
} else if (widthMode == MeasureSpec.AT_MOST) {
width = Math.min(desiredWidth, widthSize);
} else {
width = desiredWidth;
}
if (heightMode == MeasureSpec.EXACTLY) {
height = heightSize;
} else if (heightMode == MeasureSpec.AT_MOST) {
height = Math.min(desiredHeight, heightSize);
} else {
height = desiredHeight;
}
setMeasuredDimension(width, height);
}
步骤3：重写onDraw方法
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
// 获取View的宽度和高度
int width = getWidth();
int height = getHeight();
// 设置表盘的半径
int radius = Math.min(width, height) / 2;
// 设置表盘的圆心
int centerX = width / 2;
int centerY = height / 2;
// 绘制表盘背景
Paint backgroundPaint = new Paint();
backgroundPaint.setColor(Color.WHITE);
canvas.drawCircle(centerX, centerY, radius, backgroundPaint);
// 绘制表盘刻度
Paint tickPaint = new Paint();
tickPaint.setColor(Color.BLACK);
tickPaint.setStrokeWidth(3);
tickPaint.setStyle(Paint.Style.STROKE);
int tickLength = 20; // 刻度的长度
for (int i = 0; i < 12; i++) {
float angle = (float) (i * Math.PI / 6); // 计算刻度的角度
float startX = (float) (centerX + (radius - tickLength) * Math.sin(angle));
float startY = (float) (centerY - (radius - tickLength) * Math.cos(angle));
float endX = (float) (centerX + radius * Math.sin(angle));
float endY = (float) (centerY - radius * Math.cos(angle));
canvas.drawLine(startX, startY, endX, endY, tickPaint);
}
// 绘制表盘指针
Paint handPaint = new Paint();
handPaint.setColor(Color.RED);
handPaint.setStrokeWidth(6);
handPaint.setStyle(Paint.Style.STROKE);
float hour = 3; // 小时
float minute = 30; // 分钟
// 绘制小时指针
float hourAngle = (float) ((hour + minute / 60) * Math.PI / 6); // 计算小时指针的角度
float hourX = (float) (centerX + radius * 0.5 * Math.sin(hourAngle));
float hourY = (float) (centerY - radius * 0.5 * Math.cos(hourAngle));
canvas.drawLine(centerX, centerY, hourX, hourY, handPaint);
// 绘制分钟指针
float minuteAngle = (float) (minute * Math.PI / 30); // 计算分钟指针的角度
