Android-6步教你自定义View

2019-11-09 15:46:59

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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() {/* ... */} @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {/* ... */} @Override protected 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。

@Overrideprotected 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。

@Overrideprotected 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。

@Overrideprotected 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);}