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。

自定义View一共分为6步

第一步

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() {/* ... */}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {/* ... */}@Overrideprotected void onDraw(Canvas canvas) {/* ... */}
}

2.实现画笔paint类

本文一共两只画笔

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);
}

3.覆写onMeasure(…)方法

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。

@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);
}

注意：

这个方法需要至少保证一个setMeasuredDimension(..)调用，否则会报IllegalStateException错误。

4.实现onSizeChanged(…)方法

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。

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {mCenterX = w / 2f;mCenterY = h / 2f;mRadius = Math.min(w, h) / 2f;
}

5.实现onDraw(…)方法

这个方法提供了如何绘制view，它提供的Canvas类可以进行绘制。

@Override
protected void onDraw(Canvas canvas) {// draw facecanvas.drawCircle(mCenterX, mCenterY, mRadius, mCirclePaint);// draw eyesfloat 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 mouthfloat mouthInset = mRadius /3f;mArcBounds.set(mouthInset, mouthInset, mRadius * 2 - mouthInset, mRadius * 2 - mouthInset);canvas.drawArc(mArcBounds, 45f, 90f, false, mEyeAndMouthPaint);
}

6.添加你的View

<FrameLayoutxmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"><com.example.app.SmileyViewandroid:layout_width="match_parent"android:layout_height="match_parent" />
</FrameLayout>

到此就结束了，自定义View没你想的那么难

转载自：Android开发中文站 » Android-6步教你自定义View