坑爹的ViewPager

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Android开发中，常会遇到侧滑翻页的效果，android.support.v4.view.ViewPager让这种实现变得简单易用，但是通常使用时，都是让ViewPager的宽和高去match_parent，或者布局时制定了ViewPager的高度，所以一切正常。偶然的一次布局改变，着实一头雾水了半天。

场景：页面某个区域显示ViewPager用来翻页，但是ViewPager中的试图并不是设计期加上去的，所以希望ViewPager可以wrap_content自适应child的高度，布局设计好后，感觉一切良好，因为最常用的各种layout设置wrap_content都能很好的工作，ViewPager也是容器，所以认为理所当然运行正常。

真正的运行app后发现，始终无法显示我动态添加进去的child，跟踪代码也未发现异常。好吧，那我们改一下布局，设定ViewPager的高度为100dp，再次运行，靠，啥都能看见了！

这会大家应该明白了吧，ViewPager设定wrap_content无效，他不会根据child视图去计算自己的高度，网上找到了ViewPager的onMeasure的代码，如下：

     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
         // For simple implementation, or internal size is always 0.
         // We depend on the container to specify the layout size of
         // our view.  We can‘t really know what it is since we will be
         // adding and removing different arbitrary views and do not
         // want the layout to change as this happens.
         setMeasuredDimension(getDefaultSize(0, widthMeasureSpec),
                 getDefaultSize(0, heightMeasureSpec));
 
         // Children are just made to fill our space.
         mChildWidthMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredWidth() -
                 getPaddingLeft() - getPaddingRight(), MeasureSpec.EXACTLY);
         mChildHeightMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredHeight() -
                 getPaddingTop() - getPaddingBottom(), MeasureSpec.EXACTLY);
 
         // Make sure we have created all fragments that we need to have shown.
         mInLayout = true;
         populate();
         mInLayout = false;
 
         // Make sure all children have been properly measured.
         final int size = getChildCount();
         for (int i = 0; i < size; ++i) {
             final View child = getChildAt(i);
             if (child.getVisibility() != GONE) {
                 if (DEBUG) Log.v(TAG, "Measuring #" + i + " " + child
 		        + ": " + mChildWidthMeasureSpec);
                 child.measure(mChildWidthMeasureSpec, mChildHeightMeasureSpec);
             }
         }
     }

既然知道了这个原因，那如果我们需要让他适应我们自己的高度呢（假如我们添加的视图都是一样的），那么我们就继承ViewPager，然后重写onMeasure

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

	    int height = 0;
	    for(int i = 0; i < getChildCount(); i++) {
	      View child = getChildAt(i);
	      child.measure(widthMeasureSpec, MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));
	      int h = child.getMeasuredHeight();
	      if(h > height) height = h;
	    }

	    heightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY);

	    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
	  }

坑爹的ViewPager

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原文地址：http://blog.csdn.net/bdmh/article/details/48243081