详解Android如何自定义view实现圆形进度条

Android中实现进度条有很多种方式，自定义进度条一般是继承progressBar或继承view来实现，本篇中讲解的是第二种方式。

先上效果图：

实现圆形进度条总体来说并不难，还是跟往常一样继承view，初始化画笔，按下面的步骤一步步来就好了。对初学者来说动画效果可能比较陌生，我们可以使用属性动画中的valueAnimator来实现动画效果。

实现步骤：

1、画出一个灰色的圆环作为背景。

2、画出上层的圆环覆盖下方的圆环。

3、加入动画效果

值得注意的是怎么设置圆环和文字的位置。

画出矩形只需要传入矩形对角线的坐标即可，如果不加以处理的话画出来的圆环的边缘是不完整的，刚开始接触自定义view的同学们一定要先好好看看Android坐标系相关内容，不然很难理解位置参数为什么这样设置。

完整代码：

package com.example.floatingwindow.widget;
 
import android.animation.ValueAnimator;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.View;
import android.view.animation.DecelerateInterpolator;
 
import androidx.annotation.Nullable;
 
import com.example.floatingwindow.R;
 
public class ProgressBarView extends View {
 
    private Paint mPaintBack;
    private Paint mPaint;
    private Paint mPaintText;
    private float process;
    private int strokeWidth = 15;
    private int textSize = 20;
    private long duration = 3000;
    private float startDegree = 0;
    private float endDegree = 360;
    private String text = "完成";
    private String defaultText = "0%";
 
 
    public ProgressBarView(Context context) {
        super(context);
        init();
    }
 
    public ProgressBarView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }
 
    public ProgressBarView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }
 
    private void init() {
        mPaintBack = new Paint();
        mPaintBack.setColor(getResources().getColor(R.color.gray));
        mPaintBack.setStyle(Paint.Style.STROKE);
        mPaintBack.setAntiAlias(true);
        mPaintBack.setStrokeCap(Paint.Cap.ROUND);
        mPaintBack.setStrokeWidth(strokeWidth);
 
        mPaint = new Paint();
        mPaint.setColor(getResources().getColor(R.color.purple_200));
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setAntiAlias(true);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(strokeWidth);
 
        mPaintText = new Paint();
        mPaintText.setAntiAlias(true);
        mPaintText.setStyle(Paint.Style.STROKE);
        mPaintText.setColor(Color.BLACK);
        mPaintBack.setStrokeCap(Paint.Cap.ROUND);
        mPaintText.setTextSize(sp2px(textSize));
    }
 
    public void setStrokeWidth(int width) {
        strokeWidth = width;
    }
 
    public void setTextSize(int textSize) {
        this.textSize = textSize;
    }
 
    public void setDuration(long duration) {
        this.duration = duration;
    }
 
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //创建圆环矩形
        RectF rectF = new RectF(strokeWidth, strokeWidth, getWidth() - strokeWidth, getHeight() - strokeWidth);
        //画出灰色进度条作为背景
        canvas.drawArc(rectF, 0, 360, false, mPaintBack);
        //画进度条
        canvas.drawArc(rectF, 0, process, false, mPaint);
        //计算进度
        int percent = (int) (process / 360 * 100);
        //设置文字在canvas中的位置
        Paint.FontMetrics fm = mPaintText.getFontMetrics();
        int mTxtWidth = (int) mPaintText.measureText(text, 0, defaultText.length());
        int mTxtHeight = (int) Math.ceil(fm.descent - fm.ascent);
        int x = getWidth() / 2 - mTxtWidth / 2;
        int y = getHeight() / 2 + mTxtHeight / 4;
        if (percent < 100) {
            canvas.drawText(percent + "%", x, y, mPaintText);
        } else {
            canvas.drawText(text, x, y, mPaintText);
        }
    }
 
    /**
     * 设置动画效果
     */
    public void start() {
        ValueAnimator valueAnimator = ValueAnimator.ofFloat(startDegree, endDegree);
        valueAnimator.setDuration(duration);
        valueAnimator.setInterpolator(new DecelerateInterpolator());
        valueAnimator.addUpdateListener(animation -> {
            process = (float) animation.getAnimatedValue();
            invalidate();
        });
        valueAnimator.start();
    }
 
    private int sp2px(int sp) {
        return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, sp,
                getResources().getDisplayMetrics());
    }
}

最后就是动画效果了，使用valueanimator，传入开始和结束的进度以及执行时间。然后每次进度发生变化时做UI刷新。

xml布局：

MainActivity：

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
 
        progressBar.start()
 
        progressBar.setOnClickListener { progressBar.start()}
    }

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