Android 自定义View(二) onSizeChanged、onDraw、onMeasure顺序

上一篇《Android 自定义View(一) Paint、Rect、Canvas介绍》讲了最基础的如何自定义一个View，以及View用到的一些工具类。下面讲下View绘制的方法及过程

public class MyView extends View { private String TAG = "--------MyView"; private int width, height; public MyView(Context context, AttributeSet attrs) { super(context, attrs); Log.i(TAG,"MyView()"); } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); width = w; height = h; Log.i(TAG,"onSizeChanged()"); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); Log.i(TAG,"onDraw()"); Rect rect = new Rect(0, 0, width, height); Paint paint = new Paint(); paint.setColor(Color.RED); canvas.drawRect(rect, paint); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); Log.i(TAG,"onMeasure()"); } @Override protected void onFinishInflate() { super.onFinishInflate(); Log.i(TAG,"onFinishInflate()"); } }

03-15 01:28:53.111 30961-30961/com.myView I/--------MyView: MyView()
03-15 01:28:53.111 30961-30961/com.myView I/--------MyView: onFinishInflate()
03-15 01:28:53.210 30961-30961/com.myView I/--------MyView: onMeasure()
03-15 01:28:53.210 30961-30961/com.myView I/--------MyView: onMeasure()
03-15 01:28:53.520 30961-30961/com.myView I/--------MyView: onMeasure()
03-15 01:28:53.520 30961-30961/com.myView I/--------MyView: onMeasure()
03-15 01:28:53.520 30961-30961/com.myView I/--------MyView: onSizeChanged()
03-15 01:28:53.543 30961-30961/com.myView I/--------MyView: onDraw()

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1、MyView() 构造方法，这个不做解释，铁定第一个被调用。

作用：传入Context

2、onFinishInflate() 当View中所有的子控件均被映射成xml后触发

3、onMeasure() 在View放置到父容器时调用

作用：测量View的大小，也可以通过下面方式，修改View的大小

 @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); setMeasuredDimension(100,100); }

也可以通过以下方式获取控件的宽和高

    @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); int width = MeasureSpec.getSize(widthMeasureSpec);   int height = MeasureSpec.getSize(heightMeasureSpec)); }

4、onSizeChanged() 在控件大小发生改变时调用。所以这里初始化会被调用一次

作用：获取控件的宽和高度

5、onDraw() 最后就是绘制图形了