詳細可參考：http://blog.csdn.net/Beyond0525/article/details/48181345

最近專案上有一些需求，需要繪製圓形的進度條滿足設計上和互動上的需求： 

實現思路

在畫布上直接繪製View，需要了解一下幾點 
1.需要畫一個圓 
2.圓圈上有不同進度的顏色 
3.圓圈中有進度數字的展示 
4.圓圈中間還有可以自定義不同文案提示

一、畫圓

需要使用Canvas的該方法

 public void drawArc(@NonNull RectF oval, float startAngle, float sweepAngle, boolean useCenter,
            @NonNull Paint paint) {
        drawArc(oval.left, oval.top, oval.right, oval.bottom, startAngle, sweepAngle, useCenter,
                paint);
    }
 

如下：

 // 設定畫筆相關屬性
 mPaint.setAntiAlias(true);
 mPaint.setColor(Color.rgb(0xe9, 0xe9, 0xe9));
 canvas.drawColor(Color.TRANSPARENT);
 mPaint.setStrokeWidth(mCircleLineStrokeWidth);
 mPaint.setStyle(Style.STROKE);
 // 位置
 mRectF.left = mCircleLineStrokeWidth / 2; // 左上角x
 mRectF.top = mCircleLineStrokeWidth / 2; // 左上角y
 

 mRectF.right = width - mCircleLineStrokeWidth / 2; // 左下角x
 mRectF.bottom = height - mCircleLineStrokeWidth / 2; // 右下角y

 // 繪製圓圈，進度條背景
 canvas.drawArc(mRectF, -90, 360, false, mPaint);

此時畫出了預設的背景圓圈： 

二、畫進度圓弧

其實實現很簡單，換另外一種顏色同樣在畫布上畫出即可，支援此時畫的不是360°，而是通過進度計算出來的一個圓弧。

mPaint.setColor(Color.rgb(0xf8, 0x60, 0x30));
canvas.drawArc
 
(mRectF, -90, ((float) mProgress / mMaxProgress) * 360, false, mPaint);

如上即可，此時mProgress / mMaxProgress = 80/100；即可繪製出如下效果 

三、畫中間進度百分比

其實要用到Canvas中繪製文字的方法：

public void drawText(@NonNull String text, float x, float y, @NonNull Paint paint) {
   native_drawText(mNativeCanvasWrapper, text, 0, text.length(), x, y, paint.mBidiFlags,
           paint.mNativePaint, paint.mNativeTypeface);
}

如下：

// 繪製進度文案顯示
mPaint.setStrokeWidth(mTxtStrokeWidth);
String text = mProgress + "%";
int textHeight = height / 4;
mPaint.setTextSize(textHeight);
int textWidth = (int) mPaint.measureText(text, 0, text.length());
mPaint.setStyle(Style.FILL);
canvas.drawText(text, width / 2 - textWidth / 2, height / 2 + textHeight / 2, mPaint);

主要要計算好畫的位置，drawText中對應就是相關的位置，相當於居中顯示進度百分比文案。效果如下： 

四、畫圓圈中間提示文案

方法同三，只不過要計算出畫的位置即可，效果圖如下： 

五、總結

其實很多自定義的View都可以用Canvas直接畫出來，如果專案上有類似這樣的需求，可以先研究Canvas的使用和原理。 
最後附上原始碼：

public class CircleProgressView extends View {

    private static final String TAG = "CircleProgressBar";

    private int mMaxProgress = 100;

    private int mProgress = 30;

    private final int mCircleLineStrokeWidth = 8;

    private final int mTxtStrokeWidth = 2;

    // 畫圓所在的距形區域
    private final RectF mRectF;

    private final Paint mPaint;

    private final Context mContext;

    private String mTxtHint1;

    private String mTxtHint2;

    public CircleProgressView(Context context, AttributeSet attrs) {
        super(context, attrs);

        mContext = context;
        mRectF = new RectF();
        mPaint = new Paint();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int width = this.getWidth();
        int height = this.getHeight();

        if (width != height) {
            int min = Math.min(width, height);
            width = min;
            height = min;
        }

        // 設定畫筆相關屬性
        mPaint.setAntiAlias(true);
        mPaint.setColor(Color.rgb(0xe9, 0xe9, 0xe9));
        canvas.drawColor(Color.TRANSPARENT);
        mPaint.setStrokeWidth(mCircleLineStrokeWidth);
        mPaint.setStyle(Style.STROKE);
        // 位置
        mRectF.left = mCircleLineStrokeWidth / 2; // 左上角x
        mRectF.top = mCircleLineStrokeWidth / 2; // 左上角y
        mRectF.right = width - mCircleLineStrokeWidth / 2; // 左下角x
        mRectF.bottom = height - mCircleLineStrokeWidth / 2; // 右下角y

        // 繪製圓圈，進度條背景
        canvas.drawArc(mRectF, -90, 360, false, mPaint);
        mPaint.setColor(Color.rgb(0xf8, 0x60, 0x30));
        canvas.drawArc(mRectF, -90, ((float) mProgress / mMaxProgress) * 360, false, mPaint);

        // 繪製進度文案顯示
        mPaint.setStrokeWidth(mTxtStrokeWidth);
        String text = mProgress + "%";
        int textHeight = height / 4;
        mPaint.setTextSize(textHeight);
        int textWidth = (int) mPaint.measureText(text, 0, text.length());
        mPaint.setStyle(Style.FILL);
        canvas.drawText(text, width / 2 - textWidth / 2, height / 2 + textHeight / 2, mPaint);

        if (!TextUtils.isEmpty(mTxtHint1)) {
            mPaint.setStrokeWidth(mTxtStrokeWidth);
            text = mTxtHint1;
            textHeight = height / 8;
            mPaint.setTextSize(textHeight);
            mPaint.setColor(Color.rgb(0x99, 0x99, 0x99));
            textWidth = (int) mPaint.measureText(text, 0, text.length());
            mPaint.setStyle(Style.FILL);
            canvas.drawText(text, width / 2 - textWidth / 2, height / 4 + textHeight / 2, mPaint);
        }

        if (!TextUtils.isEmpty(mTxtHint2)) {
            mPaint.setStrokeWidth(mTxtStrokeWidth);
            text = mTxtHint2;
            textHeight = height / 8;
            mPaint.setTextSize(textHeight);
            textWidth = (int) mPaint.measureText(text, 0, text.length());
            mPaint.setStyle(Style.FILL);
            canvas.drawText(text, width / 2 - textWidth / 2, 3 * height / 4 + textHeight / 2, mPaint);
        }
    }

    public int getMaxProgress() {
        return mMaxProgress;
    }

    public void setMaxProgress(int maxProgress) {
        this.mMaxProgress = maxProgress;
    }

    public void setProgress(int progress) {
        this.mProgress = progress;
        this.invalidate();
    }

    public void setProgressNotInUiThread(int progress) {
        this.mProgress = progress;
        this.postInvalidate();
    }

    public String getmTxtHint1() {
        return mTxtHint1;
    }

    public void setmTxtHint1(String mTxtHint1) {
        this.mTxtHint1 = mTxtHint1;
    }

    public String getmTxtHint2() {
        return mTxtHint2;
    }

    public void setmTxtHint2(String mTxtHint2) {
        this.mTxtHint2 = mTxtHint2;
    }
}

Xml中配置：

  <com.jackshy.demo.view.CircleProgressBar
        android:id="@+id/circleProgressbar"
        android:layout_width="74dp"
        android:layout_height="74dp"
        android:layout_centerInParent="true" />

MainActivity中使用：

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;

import com.jackshy.demo.view.CircleProgressBar;

public class MainActivity extends Activity {

    private CircleProgressBar mCircleBar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initViews();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    private void initViews() {

        mCircleBar = (CircleProgressBar) findViewById(R.id.circleProgressbar);

        mCircleBar.setProgress(80);

    }

}

上述還可以做成進度條的形式，這時候需要啟動非UI執行緒呼叫此方法即可：

 public void setProgressNotInUiThread(int progress) {
        this.mProgress = progress;
        this.postInvalidate();
    }