Android自定义控件制作显示进度的Button

最近看到一些应用在下载文件的时候，并没有额外弹出进度条，而是很炫的使用启动下载任务的Button直接显示文件的下载进度，通过改变其背景色，从左向右推进，直到填满整个Button时，意味着下载任务的完成。

除了这种效果，还看到某酷的视频客户端，在观看过的视频对应的按钮上，会给该按钮添加一个描边效果，4条边，每条边代表25%的进度，由上沿开始，顺时针最终到左边沿，则代表100%的进度，这种效果也很不错。

自己也研究了一下，写了个自定义的button，下面是效果，

普通的填充效果：

描边的效果：

自定义Button的主要实现就是继承Button，并重写onDraw()方法，填充的效果实现起来相对简单一点：

 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();
      //先获取Button的边框
      canvas.getClipBounds(rect);
      rect.left += getPaddingLeft();
      //填充条的右边界根据当前进度来计算
      rect.top += getPaddingTop();
      rect.right = (rect.left - getPaddingLeft()) + (mProgress * getWidth() / 100) - getPaddingRight();
      rect.bottom -= getPaddingBottom();
      //绘制一个圆角的长条，这样相对好看一点
      canvas.drawRoundRect(new RectF(rect), 8.0f, 8.0f, mPaint);
    } 

描边效果实现起来相对复杂一点，确切说是繁琐：

     else if(currentType == TYPE_STROKE) {
      //初始化画笔
      mPaint.setAntiAlias(true);
      mPaint.setColor(getContext().getResources().getColor(R.color.green_yellow));
      mPaint.setAlpha(255);
      //获取Button的边框
      Rect rect = new Rect();
      canvas.getClipBounds(rect);
      Paint paint1, paint2, paint3, paint4;
      //根据当前进度，确定是绘制哪条边，其实也是绘制一个矩形，只不过这个矩形比较扁或是比较窄而已，类似一条边
      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);
      }
    }

记得最后执行 super.onDraw(canvas);

这样会让填充或是描边绘制在最底层，不会挡住Button原有的内容。

然后添加一个API，用于更新进度：

  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的代码上传到了github上：https://github.com/YoungLeeForeverBoy/ProgressButton

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