oncreate 获取控件大小

//------------------------------------------------方法一
int w = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
int h = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
imageView.measure(w, h);
int height =imageView.getMeasuredHeight();
int width =imageView.getMeasuredWidth();
textView.append("\n"+height+","+width);

//-----------------------------------------------方法二
ViewTreeObserver vto = imageView.getViewTreeObserver();
vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
public boolean onPreDraw() {
int height = imageView.getMeasuredHeight();
int width = imageView.getMeasuredWidth();
textView.append("\n"+height+","+width);
return true;
}
});
//-----------------------------------------------方法三
ViewTreeObserver vto2 = imageView.getViewTreeObserver();
vto2.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
@Override
public void onGlobalLayout() {
imageView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
textView.append("\n\n"+imageView.getHeight()+","+imageView.getWidth());
}
});

方法一: 比其他的两个方法多了一次计算,也就是多调用了一次onMeasure()方法,该方法虽然看上去简单,但是如果要目标控件计算耗时比较大的话(如listView等),不建议使用.

方法二,它的回调方法会调用很多次,并且滑动TextView的时候任然会调用,所以不建议使用.

方法三,比较合适.

当然,实际应用的时候需要根据实际情况而定.

view.getMeasuredHeight() - 20 <= getScrollY()+ getHeight() 

判断 控件滑到了低端

view.getMeasuredHeight()表示显示全部内容需要多大的空间

getHeight() 表示 scroll一屏幕所占的大小 布局完成之后一般不会改变

getScrollY() 表示 滑动的距离

 

    /** 
     * 比onDraw先执行 
     *  
     * 一个MeasureSpec封装了父布局传递给子布局的布局要求，每个MeasureSpec代表了一组宽度和高度的要求。 
     * 一个MeasureSpec由大小和模式组成 
     * 它有三种模式：UNSPECIFIED(未指定),父元素部队自元素施加任何束缚，子元素可以得到任意想要的大小; 
     *              EXACTLY(完全)，父元素决定自元素的确切大小，子元素将被限定在给定的边界里而忽略它本身大小； 
     *              AT_MOST(至多)，子元素至多达到指定大小的值。 
     *  
     * 　　它常用的三个函数： 　　 
     * 1.static int getMode(int measureSpec):根据提供的测量值(格式)提取模式(上述三个模式之一) 
     * 2.static int getSize(int measureSpec):根据提供的测量值(格式)提取大小值(这个大小也就是我们通常所说的大小)  
     * 3.static int makeMeasureSpec(int size,int mode):根据提供的大小值和模式创建一个测量值(格式) 
     */  
    @Override  
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  
        setMeasuredDimension(measureWidth(widthMeasureSpec), measureHeight(heightMeasureSpec));  
    }  
  
    private int measureWidth(int measureSpec) {  
        int result = 0;  
        int specMode = MeasureSpec.getMode(measureSpec);  
        int specSize = MeasureSpec.getSize(measureSpec);  
  
        if (specMode == MeasureSpec.EXACTLY) {  
            // We were told how big to be   
            result = specSize;  
        } else {  
            // Measure the text   
            result = (int) mPaint.measureText(text) + getPaddingLeft() + getPaddingRight();  
            if (specMode == MeasureSpec.AT_MOST) {  
                // Respect AT_MOST value if that was what is called for by   
                // measureSpec   
                result = Math.min(result, specSize);// 60,480   
            }  
        }  
  
        return result;  
    }  
  
    private int measureHeight(int measureSpec) {  
        int result = 0;  
        int specMode = MeasureSpec.getMode(measureSpec);  
        int specSize = MeasureSpec.getSize(measureSpec);  
  
        mAscent = (int) mPaint.ascent();  
        if (specMode == MeasureSpec.EXACTLY) {  
            // We were told how big to be   
            result = specSize;  
        } else {  
            // Measure the text (beware: ascent is a negative number)   
            result = (int) (-mAscent + mPaint.descent()) + getPaddingTop() + getPaddingBottom();  
            if (specMode == MeasureSpec.AT_MOST) {  
                // Respect AT_MOST value if that was what is called for by   
                // measureSpec   
                result = Math.min(result, specSize);  
            }  
        }  
        return result;  
    }  
}