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。
- @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 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);
- }
6.添加你的View
- <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>
到此就结束了，自定义View没你想的那么难
本文作者：佚名
来源：51CTO
