Android-6步教你自定义View

   <p>如果你打算完全定制一个View，那么你需要实现View类（所有的 Android View都实现于这个类），并且实现确定尺寸的onMeasure(…))方法和确认绘图的onDraw(…))方法。</p>    <h2>自定义View一共分为6步</h2>    <h2>第一步</h2>    <pre>  <code class="language-java">public class SmileyView extends View {      private Paint mCirclePaint;      private Paint mEyeAndMouthPaint;        private float mCenterX;      private float mCenterY;      private float mRadius;      private RectF mArcBounds = new RectF();        public SmileyView(Context context) {          this(context, null);      }        public SmileyView(Context context, AttributeSet attrs) {          this(context, attrs, 0);      }        public SmileyView(Context context, AttributeSet attrs, int defStyleAttr) {          super(context, attrs, defStyleAttr);          initPaints();      }        private void initPaints() {/* ... */}        @Override      protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {/* ... */}        @Override      protected void onDraw(Canvas canvas) {/* ... */}  }</code></pre>    <h2>2.实现画笔paint类</h2>    <p>本文一共两只画笔</p>    <pre>  <code class="language-java">private void initPaints() {      mCirclePaint = new Paint(Paint.ANTI_ALIAS_FLAG);      mCirclePaint.setStyle(Paint.Style.FILL);      mCirclePaint.setColor(Color.YELLOW);      mEyeAndMouthPaint = new Paint(Paint.ANTI_ALIAS_FLAG);      mEyeAndMouthPaint.setStyle(Paint.Style.STROKE);      mEyeAndMouthPaint.setStrokeWidth(16 * getResources().getDisplayMetrics().density);      mEyeAndMouthPaint.setStrokeCap(Paint.Cap.ROUND);      mEyeAndMouthPaint.setColor(Color.BLACK);  }</code></pre>    <h2>3.覆写onMeasure(…)方法</h2>    <p>实现这个方法告诉了母容器如何放弃自定义View，可以通过提供的measureSpecs来决定你的View的高和宽，以下是一个正方形，确认它的宽和高是一样的。</p>    <pre>  <code class="language-java">@Override  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {      int w = MeasureSpec.getSize(widthMeasureSpec);      int h = MeasureSpec.getSize(heightMeasureSpec);        int size = Math.min(w, h);      setMeasuredDimension(size, size);  }</code></pre>    <h2>注意：</h2>    <p>这个方法需要至少保证一个setMeasuredDimension(..)调用，否则会报IllegalStateException错误。</p>    <h2>4.实现onSizeChanged(…)方法</h2>    <p>这个方法是你获取View现在的宽和高. 这里我们计算的是中心和半径。</p>    <pre>  <code class="language-java">@Override  protected void onSizeChanged(int w, int h, int oldw, int oldh) {      mCenterX = w / 2f;      mCenterY = h / 2f;      mRadius = Math.min(w, h) / 2f;  }</code></pre>    <h2>5.实现onDraw(…)方法</h2>    <p>这个方法提供了如何绘制view，它提供的Canvas类可以进行绘制。</p>    <pre>  <code class="language-java">@Override  protected void onDraw(Canvas canvas) {      // draw face      canvas.drawCircle(mCenterX, mCenterY, mRadius, mCirclePaint);      // draw eyes      float eyeRadius = mRadius / 5f;      float eyeOffsetX = mRadius / 3f;      float eyeOffsetY = mRadius / 3f;      canvas.drawCircle(mCenterX - eyeOffsetX, mCenterY - eyeOffsetY, eyeRadius, mEyeAndMouthPaint);      canvas.drawCircle(mCenterX + eyeOffsetX, mCenterY - eyeOffsetY, eyeRadius, mEyeAndMouthPaint);      // draw mouth      float mouthInset = mRadius /3f;      mArcBounds.set(mouthInset, mouthInset, mRadius * 2 - mouthInset, mRadius * 2 - mouthInset);      canvas.drawArc(mArcBounds, 45f, 90f, false, mEyeAndMouthPaint);  }</code></pre>    <h2>6.添加你的View</h2>    <pre>  <code class="language-java"><FrameLayout      xmlns:android="http://schemas.android.com/apk/res/android"      android:layout_width="match_parent"      android:layout_height="match_parent">        <com.example.app.SmileyView          android:layout_width="match_parent"          android:layout_height="match_parent" />  </FrameLayout></code></pre>    <p>到此就结束了，自定义View没你想的那么难</p>    <p> </p>    <p>来自：http://www.androidchina.net/6470.html</p>    <p> </p>