Android View相关笔记

View绘制

1 View树的绘制流程

measure -> layout -> draw  树形递归遍历

2 measure

ViewGroup.LayoutParams     设定宽高，match_parent, wrap_content

MeasureSpec  32位int，最高两位表示测量模式，后30位表示该模式下的尺寸大小

MeasureSpecMode：

EXACTLY  父容器为子视图确定容器的大小

AT_MOST 父容器为子视图指定一个最大尺寸

UNSPECIFIED

measure() -> onMeasure() -> setMeasuredDimension()

3 layout

树形结构递归遍历，位置摆放

4 onDraw

invalidate() 请求系统重新渲染，触发onDraw()

requestLayout()  绘画过程中手动调用该方法，触发onMeasure(), onLayout()

当更新View时，如果尺寸大小位置和内容均发生改变，推荐先调用requestLayout()，再invalidate()

事件分发机制

DecorView是PhoneWindow的内部类，PhoneWindow继承抽象类Window.

Activity -> PhoneWindow -> DecorView = StatusBar + RootView -> ViewGroup -> View

dispatchTouchEvent(VG) -> onInterceptTouchEvent(VG) -> onTouchEvent (V)

ListView

recycleBin机制

recycleBin是AbsListView的内部类

ListView优化

1. convertView重用，添加ViewHolder
2. getView少做耗时操作
3. 三级缓存
4. 开启硬件加速
5. 减少半透明元素

    public View getView(.., View covertView, ..) {

        ViewHolder holder;

        if (convertView == null) {

            holder = new ViewHolder();

            convertView = LayoutInflator….

                … ...

            convertView.setTag(holder);

        } else {

            holder = (ViewHolder) convertView.getTag(); 

        }

    }

    class ViewHolder {  // 避免多次findViewById()

        private ImageView image;

        private TextView title;

    }

解决在onCreate()过程中获取View的宽高为0的方法

1.监听draw/layout事件

view.getViewTreeObserver().addOnGlobalLayoutListener( new ViewTreeObserver.OnGlobalLayoutListener() {

2         @Override

3         public void onGlobalLayout() {

4             mScrollView.post( new Runnable() {

5                 public void run() {

6                     view.getHeight(); // height is ready

7                 }

8             });

9         }

10 });

2.View.post推荐

UI事件队列会按顺序处理事件。在 setContentView() 被调用后，事件队列中会包含一个要求重新layout的 message ，所以任何你post到队列中的东西都会在Layout发生变化后执行。

view.post( new Runnable() {

4             @Override

5 public void run() {

6                 view.getHeight(); // height is ready

7             }

8         });

大房子左右滑动，可点击空白区域

HorizontalScrollView

bitmap.getPixel

android:scrollX

UI线程和工作线程中刷新UI

postInvalidate() invalidate()

雾霾不用于多fragment间切换，并及时销毁

mHazeImage.recycle() ;

自定义控件的属性

<declare-styleable name= "ScrollLayout" >

    <attr name= "defaultScreen" format= "integer" />

    <attr name= "customScreen" format= "integer" />

    <attr name= "customScreenHeight" format= "integer" />

    <attr name= "customScreenScale" format= "integer" />

</declare-styleable>

<com.honeywell.hch.airtouchv2.framework.view.ScrollLayout

    android :id= "@+id/control_filter_scroll"

    android :layout_width= "match_parent"

    android :layout_height= "match_parent"

    android :orientation= "vertical"

    app :customScreen= "1"

    app :customScreenHeight= "70"

    app :defaultScreen= "0 ” >

帧动画

ImageView loadingImageView = (ImageView) findViewById(R.id. enroll_loading_iv) ;

AnimationDrawable animationDrawable = (AnimationDrawable) loadingImageView.getDrawable() ;

animationDrawable.start() ;

<animation-list

    xmlns: android = " http://schemas.android.com/apk/res/android "

    android :oneshot= "false" >

    <item android :drawable= "@drawable/enroll_loading_1" android :duration= "1000" ></item>

    <item android :drawable= "@drawable/enroll_loading_2" android :duration= "1000" ></item>

    <item android :drawable= "@drawable/enroll_loading_3" android :duration= "1000" ></item>

</animation-list>

属性动画

http://www.jianshu.com/p/2412d00a0ce4

AnimatorSet popAnimation = new AnimatorSet() ;

popAnimation.playTogether(ObjectAnimator. ofFloat(view , "alpha" , 0 , 1) , ObjectAnimator

        . ofFloat(view , "translationY" , screenHeight - positionY , 0)) ;

popAnimation.setInterpolator( new OvershootInterpolator()) ;

popAnimation.setDuration( mPopUpDuration[index]) ;

popAnimation.start() ;

popAnimation.addListener( new Animator.AnimatorListener() {

动态加载View

<LinearLayout

    android :id= "@+id/all_group_layout"

    android :layout_width= "match_parent"

    android :layout_height= "wrap_content"

    android :orientation= "vertical" >

    <LinearLayout

        android :id= "@+id/group_layout"

        android :layout_width= "match_parent"

        android :layout_height= "wrap_content"

        android :orientation= "vertical" >

    </LinearLayout>

    <LinearLayout

        android :id= "@+id/un_group_layout"

        android :layout_width= "match_parent"

        android :layout_height= "wrap_content"

        android :orientation= "vertical" >

    </LinearLayout>

</LinearLayout>

// add DIY views to one group

LinearLayout oneGroup = new LinearLayout( this) ;

oneGroup.setOrientation(LinearLayout. VERTICAL) ;

AllDeviceGroupTitleView groupTitleView = new AllDeviceGroupTitleView( mContext) ; // 自定义控件

groupTitleView.setBackgroundResource( R.drawable. all_device_group_bg ) ;

groupTitleView.setGroupName(groupName) ;

oneGroup.addView(groupTitleView) ;

// add one group to group list

mGroupLayout = (LinearLayout) findViewById(R.id. group_layout ) ;

LinearLayout.LayoutParams params = new LinearLayout.LayoutParams

        (LinearLayout.LayoutParams. MATCH_PARENT , LinearLayout.LayoutParams. WRAP_CONTENT) ;

params. bottomMargin = DensityUtil. dip2px( 20) ;

oneGroup.setLayoutParams(params) ;

mGroupLayout.addView(oneGroupLayout) ;   // 注意区分点击Group还是Device

onTouchEvent()/onTouch() ／onLongClick()返回true/false问题

返回true表示该事件已消费，不会被传导下去。

返回false表示事件没有完全消费，将继续传递到子控件处理。