高仿微信6.0底部切换标签设置Alpha渐变效果解析

本文参考:【张鸿洋的博客】http://blog.csdn.net/lmj623565791/article/details/41087219

先上关键的代码

<span style="color:#333333;">public class ChangeColorIconWithTextView extends View
{

	private Bitmap mBitmap;
	private Canvas mCanvas;
	private Paint mPaint;
	/**
	 * 颜色
	 */
	private int mColor = 0xFF45C01A;
	/**
	 * 透明度 0.0-1.0
	 */
	private float mAlpha = 0f;
	/**
	 * 图标
	 */
	private Bitmap mIconBitmap;
	/**
	 * 限制绘制icon的范围
	 */
	private Rect mIconRect;
	/**
	 * icon底部文本
	 */
	private String mText = "微信";
	private int mTextSize = (int) TypedValue.applyDimension(
			TypedValue.COMPLEX_UNIT_SP, 10, getResources().getDisplayMetrics());
	private Paint mTextPaint;
	private Rect mTextBound = new Rect();

	public ChangeColorIconWithTextView(Context context)
	{
		super(context);
	}

	/**
	 * 初始化自定义属性值
	 * 
	 * @param context
	 * @param attrs
	 */
	public ChangeColorIconWithTextView(Context context, AttributeSet attrs)
	{
		super(context, attrs);

		// 获取设置的图标
		TypedArray a = context.obtainStyledAttributes(attrs,
				R.styleable.ChangeColorIconView);

		int n = a.getIndexCount();
		for (int i = 0; i < n; i++)
		{

			int attr = a.getIndex(i);
			switch (attr)
			{
			case R.styleable.ChangeColorIconView_icon:
				BitmapDrawable drawable = (BitmapDrawable) a.getDrawable(attr);
				mIconBitmap = drawable.getBitmap();
				break;
			case R.styleable.ChangeColorIconView_color:
				mColor = a.getColor(attr, 0x45C01A);
				break;
			case R.styleable.ChangeColorIconView_text:
				mText = a.getString(attr);
				break;
			case R.styleable.ChangeColorIconView_text_size:
				</span><span style="color:#ff0000;">//这个方法是转变为标准尺寸的一个函数,这里COMPLEX_UNIT_SP是单位,10是数值,也就是10sp</span><span style="color:#333333;">
				mTextSize = (int) a.getDimension(attr, TypedValue
						.applyDimension(TypedValue.COMPLEX_UNIT_SP, 10,
								getResources().getDisplayMetrics()));
				break;

			}
		}

		a.recycle();

		mTextPaint = new Paint();
		mTextPaint.setTextSize(mTextSize);
		mTextPaint.setColor(0xff555555);
		</span><span style="color:#ff0000;">// 得到text绘制范围,设给这个mTextBound值,ps这个mTextPaint仅仅是普通的Paint,但是传了mText值获得rect返回给mTextBound</span><span style="color:#333333;">
		mTextPaint.getTextBounds(mText, 0, mText.length(), mTextBound);

	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
	{
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);

		// 得到绘制icon的宽
		int bitmapWidth = Math.min(getMeasuredWidth() - getPaddingLeft()
				- getPaddingRight(), getMeasuredHeight() - getPaddingTop()
				- getPaddingBottom() - mTextBound.height());

		int left = getMeasuredWidth() / 2 - bitmapWidth / 2;
		int top = (getMeasuredHeight() - mTextBound.height()) / 2 - bitmapWidth
				/ 2;
		// 设置icon的绘制范围
		mIconRect = new Rect(left, top, left + bitmapWidth, top + bitmapWidth);

	}

	@Override
	protected void onDraw(Canvas canvas)
	{

		</span><span style="color:#ff0000;">//Round是四舍五入的。。。Ceil是向上取整。。float是向下取整</span><span style="color:#333333;">
		int alpha = (int) Math.ceil((255 * mAlpha));
		canvas.drawBitmap(mIconBitmap, null, mIconRect, null);
		setupTargetBitmap(alpha);
		drawSourceText(canvas, alpha);
		drawTargetText(canvas, alpha);
		canvas.drawBitmap(mBitmap, 0, 0, null);

	}
	
	</span><span style="color:#cc0000;">private void setupTargetBitmap(int alpha)
	{
		mBitmap = Bitmap.createBitmap(getMeasuredWidth(), getMeasuredHeight(),
				Config.ARGB_8888);
		mCanvas = new Canvas(mBitmap);
		mPaint = new Paint();
		mPaint.setColor(mColor);
		mPaint.setAntiAlias(true);
		mPaint.setDither(true);
		mPaint.setAlpha(alpha);
		mCanvas.drawRect(mIconRect, mPaint);</span>
<span style="color:#cc0000;">		mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
		mPaint.setAlpha(255);
		mCanvas.drawBitmap(mIconBitmap, null, mIconRect, mPaint);
	}</span><span style="color:#333333;">

	private void drawSourceText(Canvas canvas, int alpha)
	{
		mTextPaint.setTextSize(mTextSize);
		mTextPaint.setColor(0xff333333);
		mTextPaint.setAlpha(255 - alpha);
		canvas.drawText(mText, mIconRect.left + mIconRect.width() / 2
				- mTextBound.width() / 2,
				mIconRect.bottom + mTextBound.height(), mTextPaint);
	}
	
	private void drawTargetText(Canvas canvas, int alpha)
	{
		mTextPaint.setColor(mColor);
		mTextPaint.setAlpha(alpha);
		canvas.drawText(mText, mIconRect.left + mIconRect.width() / 2
				- mTextBound.width() / 2,
				mIconRect.bottom + mTextBound.height(), mTextPaint);
		
	}

	

	

	public void setIconAlpha(float alpha)
	{
		this.mAlpha = alpha;
		invalidateView();
	}

	private void invalidateView()
	{
		if (Looper.getMainLooper() == Looper.myLooper())
		{
			invalidate();
		} else
		{
			postInvalidate();
		}
	}

	public void setIconColor(int color)
	{
		mColor = color;
	}

	public void setIcon(int resId)
	{
		this.mIconBitmap = BitmapFactory.decodeResource(getResources(), resId);
		if (mIconRect != null)
			invalidateView();
	}

	public void setIcon(Bitmap iconBitmap)
	{
		this.mIconBitmap = iconBitmap;
		if (mIconRect != null)
			invalidateView();
	}

	private static final String INSTANCE_STATE = "instance_state";
	private static final String STATE_ALPHA = "state_alpha";

	@Override
	protected Parcelable onSaveInstanceState()
	{
		Bundle bundle = new Bundle();
		bundle.putParcelable(INSTANCE_STATE, super.onSaveInstanceState());
		bundle.putFloat(STATE_ALPHA, mAlpha);
		return bundle;
	}

	@Override
	protected void onRestoreInstanceState(Parcelable state)
	{
		if (state instanceof Bundle)
		{
			Bundle bundle = (Bundle) state;
			mAlpha = bundle.getFloat(STATE_ALPHA);
			super.onRestoreInstanceState(bundle.getParcelable(INSTANCE_STATE));
		} else
		{
			super.onRestoreInstanceState(state);
		}

	}

}</span>

上面标红的地方是实现自定义控件实现渐变切换的关键代码

private void setupTargetBitmap(int alpha)
	{
		mBitmap = Bitmap.createBitmap(getMeasuredWidth(), getMeasuredHeight(),
				Config.ARGB_8888);
		mCanvas = new Canvas(mBitmap);
		mPaint = new Paint();
		mPaint.setColor(mColor);
		mPaint.setAntiAlias(true);
		mPaint.setDither(true);
		mPaint.setAlpha(alpha);
		mCanvas.drawRect(mIconRect, mPaint);
		mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
		mPaint.setAlpha(255);
		mCanvas.drawBitmap(mIconBitmap, null, mIconRect, mPaint);
	}

这个方法的

mBitmap = Bitmap.createBitmap(getMeasuredWidth(), getMeasuredHeight(),
				Config.ARGB_8888);
		mCanvas = new Canvas(mBitmap);
		mPaint = new Paint();
		mPaint.setColor(mColor);
		mPaint.setAntiAlias(true);
		mPaint.setDither(true);
		mPaint.setAlpha(alpha);
		mCanvas.drawRect(mIconRect, mPaint);

先绘制了需要渐变显示的背景颜色,画布mCanvas绘制了一个rect区域,这个区域设置了颜色,alpha值

然后

mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));

这里摘抄一段网上的说明讲解:

Adnroid上的简单图像合成类——PorterDuffXfermode

图像合成,是将两幅退昂放在一起的动作,它使得我们能够同时看到两幅图像的特征。

我们可以首先在Canvas对象上绘制一个位图对象,然后再相同的Canvas对象上绘制第二个位图对象的方式来实现合成。不过这里在绘制第二幅图像的时候,需要在Paint对象上指定一个过渡模式(Xfermode)。

可用作过渡模式的类集合都继承自Xfermode基类,而其中包括一个成为PorterDuffXfermode的类。PorterDuffXfermode因Thomas Porter和Tom Duff而得名,他们于1984年在ACM SIGGRAPH计算机图形学出版物上发表了题为“Compositing digital images”(合成数字图像)的文章,详细介绍了一系列不同的规则,用于彼此重叠的绘制图像。

在Android的PorterDuff.Mode类中列举了他们制定的规则:

android.graphics.PorterDuff.Mode.SRC:只绘制源图像

android.graphics.PorterDuff.Mode.DST:只绘制目标图像

android.graphics.PorterDuff.Mode.DST_OVER:在源图像的顶部绘制目标图像

android.graphics.PorterDuff.Mode.DST_IN:只在源图像和目标图像相交的地方绘制目标图像

android.graphics.PorterDuff.Mode.DST_OUT:只在源图像和目标图像不相交的地方绘制目标图像

android.graphics.PorterDuff.Mode.DST_ATOP:在源图像和目标图像相交的地方绘制目标图像,在不相交的地方绘制源图像

android.graphics.PorterDuff.Mode.SRC_OVER:在目标图像的顶部绘制源图像

android.graphics.PorterDuff.Mode.SRC_IN:只在源图像和目标图像相交的地方绘制源图像

android.graphics.PorterDuff.Mode.SRC_OUT:只在源图像和目标图像不相交的地方绘制源图像

android.graphics.PorterDuff.Mode.SRC_ATOP:在源图像和目标图像相交的地方绘制源图像,在不相交的地方绘制目标图像

android.graphics.PorterDuff.Mode.XOR:在源图像和目标图像重叠之外的任何地方绘制他们,而在不重叠的地方不绘制任何内容

android.graphics.PorterDuff.Mode.LIGHTEN:获得每个位置上两幅图像中最亮的像素并显示

android.graphics.PorterDuff.Mode.DARKEN:获得每个位置上两幅图像中最暗的像素并显示

android.graphics.PorterDuff.Mode.MULTIPLY:将每个位置的两个像素相乘,除以255,然后使用该值创建一个新的像素进行显示。结果颜色=顶部颜色*底部颜色/255

android.graphics.PorterDuff.Mode.SCREEN:反转每个颜色,执行相同的操作(将他们相乘并除以255),然后再次反转。结果颜色=255-(((255-顶部颜色)*(255-底部颜色))/255)

相信通过上面的解释可以明白为什么底部标签就是一张没有颜色的图片确能实现好像有两张图在切换的效果了,原来是图片合成。。。。。。

然后

mPaint.setAlpha(255);
		mCanvas.drawBitmap(mIconBitmap, null, mIconRect, mPaint);

重新设置了alpha值最大,不透明,但是颜色没设置,会导致美工给我们切的图标的线框也显示我们设置的颜色值

然后再把图片画上去


好了,这个自定义的渐变切换标签写好了,不过大牛就是大牛,demo写的都这么严谨,比如说新手不会注意的

<span style="color:#333333;">if </span><span style="color:#ff0000;">(Looper.getMainLooper() == Looper.myLooper())</span><span style="color:#333333;">
		{
			invalidate();
		} else
		{
			postInvalidate();
		}</span>

想要了解见链接:http://leochin.com/android-looper-mainlooper/  ;

还有

private static final String INSTANCE_STATE = "instance_state";
	private static final String STATE_ALPHA = "state_alpha";

	@Override
	protected Parcelable onSaveInstanceState()
	{
		Bundle bundle = new Bundle();
		bundle.putParcelable(INSTANCE_STATE, super.onSaveInstanceState());
		bundle.putFloat(STATE_ALPHA, mAlpha);
		return bundle;
	}

	@Override
	protected void onRestoreInstanceState(Parcelable state)
	{
		if (state instanceof Bundle)
		{
			Bundle bundle = (Bundle) state;
			mAlpha = bundle.getFloat(STATE_ALPHA);
			super.onRestoreInstanceState(bundle.getParcelable(INSTANCE_STATE));
		} else
		{
			super.onRestoreInstanceState(state);
		}
	}

这个就能看出高手低手的区别了

最后关键的地方是通过OnPageChangeListener接口里的onPageScrolled方法实现渐变效果了

<span style="color:#333333;">@Override
	public void onPageScrolled</span><span style="color:#cc0000;">(int position, float positionOffset,
			int positionOffsetPixels)</span><span style="color:#333333;">
	{
		// Log.e("TAG", "position = " + position + " , positionOffset = "
		// + positionOffset);

		if (positionOffset > 0)
		{
			ChangeColorIconWithTextView left = mTabIndicator.get(position);
			ChangeColorIconWithTextView right = mTabIndicator.get(position + 1);

			left.setIconAlpha(1 - positionOffset);
			right.setIconAlpha(positionOffset);
		}

	}</span>
</pre><p></p><p><span style="font-family:Arial; color:#333333"><span style="font-size:14px; line-height:26px">positionOffset这个参数是一个左滑从0到1最后置0的值,右滑从1到0的值,通过log数据可以分析出来,正是因为这个特性,所以可以很方便实现自定义view的重绘</span></span></p><p><span style="font-family:Arial; color:#333333"><span style="font-size:14px; line-height:26px">再附网上的一段代码</span></span></p><p></p><pre name="code" class="java"> @Override
 71         public void onPageScrolled(int arg0, float arg1, int arg2) {
 72             if (isScrolling) {
 73                 if (lastValue > arg2) {
 74                     // 递减,向右侧滑动
 75                     right = true;
 76                     left = false;
 77                 } else if (lastValue < arg2) {
 78                     // 递减,向右侧滑动
 79                     right = false;
 80                     left = true;
 81                 } else if (lastValue == arg2) {
 82                     right = left = false;
 83                 }
 84             }
 85             Log.i("meityitianViewPager",
 86                     "meityitianViewPager onPageScrolled  last :arg2  ,"
 87                             + lastValue + ":" + arg2);
 88             lastValue = arg2;
 89         }

由于上面讲解的都是对网上大牛博客进行学习的,如果有冒犯之处见谅,有疑问留言

高仿微信6.0底部切换标签设置Alpha渐变效果解析

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