編輯：關於Android編程
3.1 Android控件架構 3.2 View的測量 3.3 View的繪制 3.4 ViewGroup的測量 3.5 ViewGroup的繪制 3.6 自定義View
3.6.1 對現有的空間進行拓展 3.6.2 創建復合控件 3.6.3 重寫View來實現全新的空間 3.7 自定義ViewGroup 3.8 事件攔截機制分析
控件大致非為兩類：
view控件：視圖控件 viewGroup控件：包含多個View控件，並管理其包含的View控件 兩者之間的關系：上層控件負責下層子控件的測量與繪制，並傳遞交互事件UI界面架構：
Activity都包含一個Window對象，通常由PhoneWindow來實現 PhoneWindow將一個DecorView設置為整個應用窗口的根View
DecorView為整個Window界面的最頂層View DecorView只有一個子元素為LinearLayout，代表整個Window界面，包含通知欄，標題欄，內容顯示欄三塊區域 LinearLayout裡有兩個FrameLayout子元素：
標題欄顯示界面。只有一個TextView顯示應用的名稱 內容欄顯示界面。就是setContentView()方法載入的布局界面
MeasureSpec類：32位的int值，高2位為測量模式，低30位為測量大小
MeasureSpec模式：
EXACTLY：精確模式 ，當控件的layout_width屬性或layout_height屬性指定為具體值，控件大小也是該具體值 AT_MOST：最大值模式，當控件layout_width屬性或layout_height屬性指定為warp_content時，控件的尺寸不要超過父控件允許的最大尺寸 UNSPECIFIED：未指定模式，控件要多大就多大，通常情況下再繪制自定義View中才會使用View類默認的onMeasure()方法只支持EXACTLY模式，View需要支持warp_content屬性，那麼就必須重寫onMeasure()方法，來制定warp_content的大小
下面我們通過一個簡單的實例，演示如何進行View的測量，首先，需要重寫onMeasure()方法：
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
可以發現，onMeasure方法調用了父類的onMeasure方法，代碼跟蹤父類onMeasure方法
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
}
可以發現，系統最終會調用setMeasuredDimension(int measuredWidth，int measuredHeight)方法將測量後的寬高值設置進去，我們調用自定義的measureWidth()方法和measureHeight()方法，分別對寬高進行重新定義
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(measureWidth(widthMeasureSpec),measureHeight(heightMeasureSpec));
}
下面以measureWidth()方法為例：
第一步：從MeasureSpec對象中提取出具體的測量模式和大小
int specMode = MeasureSpec.getMode(measureSpec); int specSize = MeasureSpec.getSize(measureSpec);
第二步：通過不同的測量模式給出不同的測量值：
EXACTLY：使用指定的specSize即可 AT_MOST：取出我們指定的大小和SpecSize的最小值 UNSPECIFIED：200px下面這段代碼基本上可以作為模板代碼：
private int measureWidth(int measureSpec) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
if (specMode == MeasureSpec.EXACTLY) {
result = specSize;
} else {
result = 200;
if (specMode == MeasureSpec.AT_MOST) {
result = Math.min(result, specSize);
}
}
return result;
}
可以發現，當指定warp_content屬性時，View就獲得一個默認值200px
當測量好了一個View之後，我們通過重寫View類中的onDraw()方法來繪圖，要想繪制相應的圖像，就必須在Canvas上進行繪制
Canvas canvas = new Canvas(Bitmap);
Canvas就像是一個畫板，我們傳進去一個bitmap，通過這個bitmap創建的Canvas畫布緊緊聯系在一起，這個過程我們稱之為裝載畫布，這個bitmap用來存儲所有繪制在Canvas上的像素信息，所以當你在後面調用所有的Canvas.drawxxx方法都會發生在這個bitmap上
ViewGroup在測量時通過遍歷所有子View，從而調用子View的Measure方法來獲得每一個子View的結果
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int childCount = getChildCount();
for (int i = 0; i < childCount; i++) {
getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
}
}
ViewGroup測量完畢後，通常會去重寫onLayout()方法來控制其子View顯示位置的邏輯
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
for (int i = 0; i < getChildCount(); i++) {
this.getChildAt(i).layout(l, t, r, b);
}
}
ViewGroup通常不需要繪制，如果不是指定ViewGroup的背景顏色，那麼ViewGroup的onDraw()方法都不會被調用，但是，ViewGroup會使用dispatchDraw()方法來繪制子View
@Override
protected void dispatchDraw(Canvas canvas) {
super.dispatchDraw(canvas);
}
在View中通常有以下一些重要的回調方法：
onFinishInflate()：從XML加載組件後回調 onSizeChanged()：組件大小改變時回調 onMeasure()：回調該方法來進行測量 onLayout()：回調該方法來確定顯示的位置 onTouchEvent()：監聽到觸摸事件時回調通常情況下，有以下三種方法來實現自定義的控件：
對現有的控件進行拓展 通過組合來實現新的控件 重寫View來實現全新的控件
3.6.1 對現有的控件進行拓展
自定義修改TextView……見經典代碼回顧，案例一 閃動的文字效果……見經典代碼回顧，案例二
3.6.2 創建復合控件
自定義ToolBar的實現……見經典代碼回顧，案例三
3.6.3 重寫View來實現全新的控件
弧線展示圖……見經典代碼回顧，案例四 音頻條形圖……見經典代碼回顧，案例五
自定義ViewGroup，仿ScrollView……見經典代碼回顧，案例六
事件攔截機制三個重要方法
dispatchTouchEvent()：分發事件 onInterceptTouchEvent()：攔截事件 onTouchEvent()：處理事件舉一個例子說明事件分發機制：
ViewGroupA：處於視圖最下層 ViewGroupB：處於視圖中間層 View：處於視圖最上層正常的事件分發機制流程：
ViewGroupA dispatchTouchEvent ViewGroupA onInterceptTouchEvent ViewGroupB dispatchTouchEvent ViewGroupB onInterceptTouchEvent View dispatchTouchEvent View onTouchEvent ViewGroupB onTouchEvent ViewGroupA onTouchEvent若ViewGroupB的onInterceptTouchEvent()方法返回true的分發機制流程：
ViewGroupA dispatchTouchEvent ViewGroupA onInterceptTouchEvent ViewGroupB dispatchTouchEvent ViewGroupB onInterceptTouchEvent ViewGroupB onTouchEvent ViewGroupA onTouchEvent若View的onTouchEvent()方法返回true的分發機制流程：
ViewGroupA dispatchTouchEvent ViewGroupA onInterceptTouchEvent ViewGroupB dispatchTouchEvent ViewGroupB onInterceptTouchEvent View dispatchTouchEvent View onTouchEvent若ViewGroupB的onTouchEvent()方法返回true的分發機制流程：
ViewGroupA dispatchTouchEvent ViewGroupA onInterceptTouchEvent ViewGroupB dispatchTouchEvent ViewGroupB onInterceptTouchEvent View dispatchTouchEvent View onTouchEvent ViewGroupB onTouchEvent簡單的說dispatchTouchEvent()和onInterceptTouchEvent()是從下往上一層一層分發下去的，而onTouchEvent()是從上往下一層一層分發下去的
public class CustomTextView extends TextView {
private Paint paint1, paint2;
public CustomTextView(Context context, AttributeSet attrs) {
super(context, attrs);
initPaint();
}
/**
* 初始化畫筆
*/
private void initPaint() {
paint1 = new Paint();
paint1.setColor(getResources().getColor(android.R.color.holo_blue_light));
paint1.setStyle(Paint.Style.FILL);
paint2 = new Paint();
paint2.setColor(Color.YELLOW);
paint2.setStyle(Paint.Style.FILL);
}
@Override
protected void onDraw(Canvas canvas) {
//繪制外層矩形
canvas.drawRect(0, 0, getMeasuredWidth(), getMeasuredHeight(), paint1);
//繪制內層矩形
canvas.drawRect(10, 10, getMeasuredWidth() - 10, getMeasuredHeight() - 10, paint2);
canvas.save();
//繪制文字前平移10像素
canvas.translate(10, 0);
//父類完成的方法，即繪制文本
super.onDraw(canvas);
canvas.restore();
}
}
![\](https://android.yunyiwangluo.com/Android/UploadFiles_5356/201702/2017022216591442.png "\")
public class FlashTextView extends TextView {
int mViewWidth = 0;
private Paint mPaint;
private LinearGradient mLinearGradient;
private Matrix matrix;
private int mTranslate;
public FlashTextView(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
if (mViewWidth == 0) {
mViewWidth = getMeasuredWidth();
if (mViewWidth > 0) {
mPaint = getPaint();
mLinearGradient = new LinearGradient(0, 0, mViewWidth, 0, new int[]{Color.BLUE, 0xffffffff, Color.BLUE},
null, Shader.TileMode.CLAMP);
mPaint.setShader(mLinearGradient);
matrix = new Matrix();
}
}
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if (matrix != null) {
mTranslate += mViewWidth + 5;
if (mTranslate > 2 * mViewWidth / 5) {
mTranslate = -mViewWidth;
}
matrix.setTranslate(mTranslate, 0);
mLinearGradient.setLocalMatrix(matrix);
postInvalidateDelayed(100);
}
}
}
![\](https://android.yunyiwangluo.com/Android/UploadFiles_5356/201702/2017022216591456.gif "\")
在values文件夾中創建一個attrs.xml文件來自定義屬性
開始創建我們的ToolBar
public class ToolBar extends RelativeLayout {
private int mLeftTextColor;
private Drawable mLeftBackground;
private String mLeftText;
private int mRightTextColor;
private Drawable mRightBackgroup;
private String mRightText;
private float mTitleTextSize;
private int mTitleTextColor;
private String mTitle;
private Button mLeftButton;
private Button mRightButton;
private TextView mTitleView;
private RelativeLayout.LayoutParams mLeftParams;
private RelativeLayout.LayoutParams mRightParams;
private RelativeLayout.LayoutParams mTitleParams;
//帶參構造方法
public ToolBar(Context context, AttributeSet attrs) {
super(context, attrs);
//通過這個方法，將你在attrs.xml文件中定義的declare-styleable
//的所有屬性的值存儲到TypedArray中
TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.TopBar);
//從TypedArray中取出對應的值來設置的屬性賦值
mLeftTextColor = ta.getColor(R.styleable.TopBar_leftTextColor, 0);
mLeftBackground = ta.getDrawable(R.styleable.TopBar_leftBackground);
mLeftText = ta.getString(R.styleable.TopBar_leftText);
mRightTextColor = ta.getColor(R.styleable.TopBar_rightTextColor, 0);
mRightBackgroup = ta.getDrawable(R.styleable.TopBar_rightBackground);
mRightText = ta.getString(R.styleable.TopBar_rightText);
mTitleTextSize = ta.getDimension(R.styleable.TopBar_titleTextSize, 10);
mTitleTextColor = ta.getColor(R.styleable.TopBar_titleTextColor, 0);
mTitle = ta.getString(R.styleable.TopBar_title);
//獲取完TypedArray的值之後，一般要調用recycle方法來避免重復創建時候的錯誤
ta.recycle();
mLeftButton = new Button(context);
mRightButton = new Button(context);
mTitleView = new TextView(context);
//為創建的元素賦值
mLeftButton.setTextColor(mLeftTextColor);
mLeftButton.setBackground(mLeftBackground);
mLeftButton.setText(mLeftText);
mRightButton.setTextColor(mRightTextColor);
mRightButton.setBackground(mRightBackgroup);
mRightButton.setText(mRightText);
mTitleView.setText(mTitle);
mTitleView.setTextColor(mTitleTextColor);
mTitleView.setTextSize(mTitleTextSize);
mTitleView.setGravity(Gravity.CENTER);
//為組件元素設置相應的布局元素
mLeftParams = new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.MATCH_PARENT);
mLeftParams.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
addView(mLeftButton, mLeftParams);
mRightParams = new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.MATCH_PARENT);
mRightParams.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
addView(mRightButton, mRightParams);
mTitleParams = new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.MATCH_PARENT);
mTitleParams.addRule(RelativeLayout.CENTER_IN_PARENT);
addView(mTitleView, mTitleParams);
}
}
在布局文件中使用
![\](https://android.yunyiwangluo.com/Android/UploadFiles_5356/201702/2017022216591408.png "\")
public class CircleProgressView extends View {
private int mCircleXY;
private int length;
private float mRadius;
private Paint mCirclePaint;
private Paint mArcPaint;
private Paint mTextPaint;
private String mShowText = "Hensen_";
private int mTextSize = 25;
private float mSweepValue = 270;
public CircleProgressView(Context context, AttributeSet attrs) {
super(context, attrs);
//獲取屏幕高寬
WindowManager wm = (WindowManager) getContext()
.getSystemService(Context.WINDOW_SERVICE);
length = wm.getDefaultDisplay().getWidth();
init();
}
private void init() {
mCircleXY = length / 2;
mRadius = (float) (length * 0.5 / 2);
mCirclePaint = new Paint();
mCirclePaint.setColor(Color.BLUE);
mArcPaint = new Paint();
mArcPaint.setStrokeWidth(50);
mArcPaint.setStyle(Paint.Style.STROKE);
mArcPaint.setColor(Color.BLUE);
mTextPaint = new Paint();
mTextPaint.setColor(Color.WHITE);
mTextPaint.setTextSize(mTextSize);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
//矩形
RectF mArcRectF = new RectF((float) (length * 0.1), (float) (length * 0.1), (float) (length * 0.9), (float) (length * 0.9));
//繪制圓
canvas.drawCircle(mCircleXY, mCircleXY, mRadius, mCirclePaint);
//繪制弧線
canvas.drawArc(mArcRectF, 270, mSweepValue, false, mArcPaint);
//繪制文字
canvas.drawText(mShowText, 0, mShowText.length(), mCircleXY, mCircleXY + (mTextSize / 4), mTextPaint);
}
public void setSweepValue(float sweepValue) {
if (sweepValue != 0) {
mSweepValue = sweepValue;
} else {
mSweepValue = 25;
}
invalidate();
}
}
當用戶不指定具體的比例值時，可以調用以下代碼來設置相應的比例值
CircleProgressView circleProgressView = (CircleProgressView) findViewById(R.id.circle); circleProgressView.setSweepValue(270);
![\](https://android.yunyiwangluo.com/Android/UploadFiles_5356/201702/2017022216591492.png "\")
public class MusicView extends View {
private int mWidth;
private int mRectHeight;
private int mRectWidth;
private int mRectCount = 20;
private LinearGradient mLinearGradient;
private Paint mPaint=new Paint();
private float currentHeight;
private int offset = 5;
private double mRandom;
public MusicView(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
mWidth = getWidth();
mRectHeight = getHeight();
mRectWidth = (int) (mWidth * 0.6 / mRectCount);
mLinearGradient = new LinearGradient(0, 0, mRectWidth, mRectHeight, Color.YELLOW, Color.BLUE, Shader.TileMode.CLAMP);
mPaint.setShader(mLinearGradient);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
//遍歷繪制矩形，留中間間隔
for (int i = 0; i < mRectCount; i++) {
//開始繪制
canvas.drawRect((float) (mWidth * 0.4 / 2 + mRectWidth * i + offset),
currentHeight, (float) (mWidth * 0.4 / 2 + mRectWidth * (i + 1)), mRectHeight, mPaint);
}
//獲取隨機數
mRandom = Math.random();
currentHeight = ((float) (mRectHeight * mRandom));
//延遲300去刷新
postInvalidateDelayed(300);
}
}
![\](https://android.yunyiwangluo.com/Android/UploadFiles_5356/201702/2017022216591467.gif "\")
自定義的ScrollView沒有系統自帶的性能好，畢竟很多因素都沒考慮到，這裡只是適用於練手使用
public class CustomScrollView extends ViewGroup {
private int mScreenHeight;
private Scroller mScroller;
private int mLastY;
private int mStart;
private int mEnd;
public CustomScrollView(Context context, AttributeSet attrs) {
super(context, attrs);
//獲取屏幕高寬
WindowManager wm = (WindowManager) getContext()
.getSystemService(Context.WINDOW_SERVICE);
mScreenHeight = wm.getDefaultDisplay().getHeight();
mScroller = new Scroller(getContext());
}
@Override
protected void onLayout(boolean b, int i, int i1, int i2, int i3) {
int childCount = getChildCount();
MarginLayoutParams mlp = (MarginLayoutParams) getLayoutParams();
mlp.height = mScreenHeight * childCount;
setLayoutParams(mlp);
for (int j = 0; j < childCount; j++) {
View child = getChildAt(j);
if (child.getVisibility() != View.GONE) {
child.layout(i, j * mScreenHeight, i2, (j + 1) * mScreenHeight);
}
}
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int count = getChildCount();
for (int i = 0; i < count; ++i) {
View childView = getChildAt(i);
measureChild(childView, widthMeasureSpec, heightMeasureSpec);
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mLastY = y;
mStart = getScrollY();
break;
case MotionEvent.ACTION_MOVE:
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
int dy = mLastY - y;
if (getScrollY() < 0) {
dy = 0;
}
if (getScrollY() > getHeight() - mScreenHeight) {
dy = 0;
}
scrollBy(0, dy);
mLastY = y;
break;
case MotionEvent.ACTION_UP:
mEnd = getScrollY();
int dScrollY = mEnd - mStart;
if (dScrollY > 0) {
if (dScrollY < mScreenHeight / 3) {
mScroller.startScroll(0, getScrollY(), 0, -dScrollY);
} else {
mScroller.startScroll(0, getScrollY(), 0, mScreenHeight - dScrollY);
}
} else {
if (-dScrollY < mScreenHeight / 3) {
mScroller.startScroll(0, getScrollY(), 0, -dScrollY);
} else {
mScroller.startScroll(0, getScrollY(), 0, -mScreenHeight - dScrollY);
}
}
break;
}
postInvalidate();
return true;
}
@Override
public void computeScroll() {
super.computeScroll();
if (mScroller.computeScrollOffset()) {
scrollTo(0, mScroller.getCurrY());
}
}
}
在布局中使用
![\](https://android.yunyiwangluo.com/Android/UploadFiles_5356/201702/2017022216591526.gif "\")
經典回顧源碼下載
github：https://github.com/CSDNHensen/QunYingZhuang
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