Android 自定義View(二) onSizeChanged、onDraw、onMeasure順序

上一篇《Android 自定義View(一) Paint、Rect、Canvas介紹》講了最基礎的如何自定義一個View，以及View用到的一些工具類。下面講下View繪制的方法及過程

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() 構造方法，這個不做解釋，鐵定第一個被調用。

作用：傳入Context

2、onFinishInflate() 當View中所有的子控件均被映射成xml后觸發

3、onMeasure() 在View放置到父容器時調用

作用：測量View的大小，也可以通過下面方式，修改View的大小

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

也可以通過以下方式獲取控件的寬和高

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

4、onSizeChanged() 在控件大小發生改變時調用。所以這里初始化會被調用一次

作用：獲取控件的寬和高度

5、onDraw() 最后就是繪制圖形了