1.系統(tǒng)ProgressBar樣式實(shí)現(xiàn)原理分析

普通的一直圓形轉(zhuǎn)的ProgressBar

<style name="Widget.ProgressBar">
    <item name="indeterminateOnly">true</item>
    <item name="indeterminateDrawable">@drawable/progress_medium_white</item>
    <item name="indeterminateBehavior">repeat</item>
    <item name="indeterminateDuration">3500</item>
    <item name="minWidth">48dip</item>
    <item name="maxWidth">48dip</item>
    <item name="minHeight">48dip</item>
    <item name="maxHeight">48dip</item>
    <item name="mirrorForRtl">false</item>
</style> 

上面的“@drawable/progress_medium_white” 是一個(gè)幀動(dòng)畫(huà)

水平的ProgressBar

<style name="Widget.ProgressBar.Horizontal">
    <item name="indeterminateOnly">false</item>
    <item name="progressDrawable">@drawable/progress_horizontal</item>
    <item name="indeterminateDrawable">@drawable/progress_indeterminate_horizontal</item>
    <item name="minHeight">20dip</item>
    <item name="maxHeight">20dip</item>
    <item name="mirrorForRtl">true</item>
</style>

@drawable/progress_indeterminate_horizontal：是一個(gè)幀動(dòng)畫(huà)

@drawable/progress_horizontal：是一個(gè)LayerDrawable，主要由一個(gè)表示底色的Drawable，和表示Progress的ClipDrawable組成

<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:id="@android:id/background">
        <shape>
            <corners android:radius="5dip" />
            <gradient
                .....................
            />
        </shape>
    </item>
....................
<item android:id="@android:id/progress">
        <clip>
            <shape>
                <corners android:radius="5dip" />
                <gradient
                    .....................
                />
            </shape>
        </clip>
    </item>
</layer-list>

小結(jié)：
一直旋轉(zhuǎn)的系統(tǒng)ProgressBar，其實(shí)只是一直播放的幀動(dòng)畫(huà)
水平的ProgressBar，是由于ClipDrawable根據(jù)Progress，從而改變ClipDrawable的Level

2.方案選擇

1. 參考系統(tǒng)水平ProgressBar的樣式實(shí)現(xiàn)，自定義特殊的Drawable，傳入ProgressBar（由于是系統(tǒng)實(shí)現(xiàn)，優(yōu)先考慮）
2. 繼承ProgressBar，重寫(xiě)里面的Draw方法

3.方案一

1. 自定義一個(gè)Drawable，重寫(xiě)里面的Draw方法，繪制一個(gè)圓角矩形作為底色
2. 再自定義一個(gè)Drawable，重寫(xiě)里面的Draw方法，根據(jù)Level值，繪制一個(gè)當(dāng)前的進(jìn)度
3. 通過(guò)LayerDrawable把這兩個(gè)Drawable層疊起來(lái)，得到最后的LayerDrawable
4. 調(diào)用ProgressBar的setProgressDrawable，設(shè)置該LayerDrawable

結(jié)果：失敗。通過(guò)代碼調(diào)用ProgressBar的setProgressDrawable發(fā)現(xiàn)調(diào)用無(wú)效，不解。

4.方案二

1. 生成一個(gè)矩形：RectF rectF = new RectF(mPathWidth,mPathWidth,getWidth()-mPathWidth,getHeight()-mPathWidth);
   注意：因?yàn)槭侵灰吙颍陨傻木匦我獪p去邊框的寬度
2. 生成圓角矩形的Path
3. 利用PathMeasure，獲取Path的某一部分，并繪制到Canvas

具體代碼：https://github.com/yinfork/Android-Dev-Demos/blob/master/app/src/main/java/com/inkenka/devdemos/processbar/RoundCornerProgressBar.java

public class RoundCornerProgressBar extends ProgressBar {
    private Paint mBackgroundPaint = new Paint();
    private Paint mProgressPaint = new Paint();
    private float mRadius;
    private int mPathWidth;
    private float mStartOffsetPercent;

構(gòu)造函數(shù)（略）
 
    @Override
    public void onDraw(Canvas canvas) {
        drawBackground(canvas);
        drawProgress(canvas);
    }

    private void drawBackground(Canvas canvas){
        RectF rectF = new RectF(mPathWidth,mPathWidth,getWidth()-mPathWidth,getHeight()-mPathWidth);
        canvas.drawRoundRect(rectF, mRadius, mRadius, mBackgroundPaint);
    }

    private void drawProgress(Canvas canvas){
        RectF rectF = new RectF(mPathWidth,mPathWidth,getWidth()-mPathWidth,getHeight()-mPathWidth);
        Path path = new Path();

        path.addRoundRect(rectF, mRadius, mRadius, Path.Direction.CW);

        Path mRenderPaths = new Path();
        PathMeasure mPathMeasure = new PathMeasure(path, false);

        float pathOffset = mPathMeasure.getLength() * (getProgress()/100f);
        float startOffset = mPathMeasure.getLength() * mStartOffsetPercent;

        if(pathOffset + startOffset < mPathMeasure.getLength()){
            if (mPathMeasure.getSegment(startOffset, startOffset + pathOffset, mRenderPaths, true)) {
                canvas.drawPath(mRenderPaths, mProgressPaint);
            }
        } else {
            if (mPathMeasure.getSegment(startOffset, mPathMeasure.getLength(), mRenderPaths, true)) {
                canvas.drawPath(mRenderPaths, mProgressPaint);
            }
            if (mPathMeasure.getSegment(0, pathOffset + startOffset - mPathMeasure.getLength(), mRenderPaths, true)) {
                canvas.drawPath(mRenderPaths, mProgressPaint);
            }
        }
    }
}