Android自定義控件制作顯示進度的Button

最近看到一些應用在下載文件的時候，並沒有額外彈出進度條，而是很炫的使用啟動下載任務的Button直接顯示文件的下載進度，通過改變其背景色，從左向右推進，直到填滿整個Button時，意味著下載任務的完成。

除了這種效果，還看到某酷的視頻客戶端，在觀看過的視頻對應的按鈕上，會給該按鈕添加一個描邊效果，4條邊，每條邊代表25%的進度，由上沿開始，順時針最終到左邊沿，則代表100%的進度，這種效果也很不錯。

自己也研究了一下，寫了個自定義的button，下面是效果， 

普通的填充效果： 

描邊的效果： 

自定義Button的主要實現就是繼承Button，並重寫onDraw()方法，填充的效果實現起來相對簡單一點：

 if(currentType == TYPE_FILL) {
      mPaint.setColor(getContext().getResources().getColor(R.color.green_yellow));
      mPaint.setAntiAlias(true);
      mPaint.setAlpha(128);
      mPaint.setStrokeWidth(1.0f);
      Rect rect = new Rect();
      //先獲取Button的邊框
      canvas.getClipBounds(rect);
      rect.left += getPaddingLeft();
      //填充條的右邊界根據當前進度來計算
      rect.top += getPaddingTop();
      rect.right = (rect.left - getPaddingLeft()) + (mProgress * getWidth() / 100) - getPaddingRight();
      rect.bottom -= getPaddingBottom();
      //繪制一個圓角的長條，這樣相對好看一點
      canvas.drawRoundRect(new RectF(rect), 8.0f, 8.0f, mPaint);
    } 

描邊效果實現起來相對復雜一點，確切說是繁瑣：

     else if(currentType == TYPE_STROKE) {
      //初始化畫筆
      mPaint.setAntiAlias(true);
      mPaint.setColor(getContext().getResources().getColor(R.color.green_yellow));
      mPaint.setAlpha(255);
      //獲取Button的邊框
      Rect rect = new Rect();
      canvas.getClipBounds(rect);
      Paint paint1, paint2, paint3, paint4;
      //根據當前進度，確定是繪制哪條邊，其實也是繪制一個矩形，只不過這個矩形比較扁或是比較窄而已，類似一條邊
      if(mProgress >= 0 && mProgress < 25) {
        paint1 = new Paint(mPaint);
        Rect temp = new Rect(rect.left + getPaddingLeft(),
            rect.top + getPaddingTop(),
            rect.left + mProgress * (getWidth() - getPaddingLeft() - getPaddingRight())
                / 25 - getPaddingRight(),
            rect.top + getPaddingTop() + 2);
        canvas.drawRect(temp, paint1);
      } else if(mProgress < 50) {
        paint1 = new Paint(mPaint);
        Rect rect1 = new Rect(rect.left + getPaddingLeft(),
            rect.top + getPaddingTop(), rect.right - getPaddingRight(),
            rect.top + getPaddingTop() + 2);
        canvas.drawRect(rect1, paint1);

        paint2 = new Paint(mPaint);
        Rect rect2 = new Rect(rect.right - getPaddingRight() - 2,
            rect.top + getPaddingTop(), rect.right - getPaddingRight(),
            rect.top + getPaddingTop() + (mProgress - 25) *
                (getHeight() - getPaddingTop() - getPaddingBottom()) / 25);
        canvas.drawRect(rect2, paint2);
      } else if(mProgress < 75) {
        paint1 = new Paint(mPaint);
        Rect rect1 = new Rect(rect.left + getPaddingLeft(),
            rect.top + getPaddingTop(), rect.right - getPaddingRight(),
            rect.top + getPaddingTop() + 2);
        canvas.drawRect(rect1, paint1);

        paint2 = new Paint(mPaint);
        Rect rect2 = new Rect(rect.right - getPaddingRight() - 2,
            rect.top + getPaddingTop(), rect.right - getPaddingRight(),
            rect.bottom - getPaddingBottom());
        canvas.drawRect(rect2, paint2);

        paint3 = new Paint(mPaint);
        Rect rect3 = new Rect(
            rect.right - getPaddingRight() - (mProgress - 50) *
                (getWidth() - getPaddingLeft() - getPaddingRight()) / 25,
            rect.bottom - getPaddingBottom() - 2,
            rect.right - getPaddingRight(),
            rect.bottom - getPaddingBottom());
        canvas.drawRect(rect3, paint3);
      } else if(mProgress <= 100) {
        paint1 = new Paint(mPaint);
        Rect rect1 = new Rect(
            rect.left + getPaddingLeft(),
            rect.top + getPaddingTop(), rect.right - getPaddingRight(),
            rect.top + getPaddingTop() + 2);
        canvas.drawRect(rect1, paint1);

        paint2 = new Paint(mPaint);
        Rect rect2 = new Rect(
            rect.right - getPaddingRight() - 2,
            rect.top + getPaddingTop(), rect.right - getPaddingRight(),
            rect.bottom - getPaddingBottom());
        canvas.drawRect(rect2, paint2);

        paint3 = new Paint(mPaint);
        Rect rect3 = new Rect(
            rect.left + getCompoundPaddingLeft(),
            rect.bottom - getPaddingBottom() - 2, rect.right - getPaddingRight(),
            rect.bottom - getPaddingRight());
        canvas.drawRect(rect3, paint3);

        paint4 = new Paint(mPaint);
        Rect rect4 = new Rect(
            rect.left + getCompoundPaddingLeft(),
            rect.bottom - getPaddingBottom() - (mProgress - 75) *
                (getHeight() - getPaddingTop() - getPaddingBottom()) / 25,
            rect.left + getPaddingLeft() + 2,
            rect.bottom - getPaddingBottom());
        canvas.drawRect(rect4, paint4);
      }
    } 

記得最後執行 super.onDraw(canvas);

這樣會讓填充或是描邊繪制在最底層，不會擋住Button原有的內容。

然後添加一個API，用於更新進度： 

  public void updateProgress(int progress) {
    if(progress >= 0 && progress <= 100) {
      mProgress = progress;
      invalidate();
    } else if(progress < 0) {
      mProgress = 0;
      invalidate();
    } else if(progress > 100) {
      mProgress = 100;
      invalidate();
    }
  } 

Demo的代碼上傳到了github上：https://github.com/YoungLeeForeverBoy/ProgressButton

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