Android中FlowLayout组件实现瀑布流效果

class ZSFlowLayout : ViewGroup {
    constructor(context: Context) : super(context) {}
 
    
    constructor(context: Context, attr: AttributeSet) : super(context, attr) {}
 
    constructor (context: Context, attr: AttributeSet, defZStyle: Int) : super(
        context,
        attr,
        defZStyle
    ) {
    }
 
}

 public final View createView(@NonNull Context viewContext, @NonNull String name,
            @Nullable String prefix, @Nullable AttributeSet attrs)
            throws ClassNotFoundException, InflateException {
        Objects.requireNonNull(viewContext);
        Objects.requireNonNull(name);
 
        //从缓存中取对应的构造函数
        Constructor<? extends View> constructor = sConstructORMap.get(name);
       
        Class<? extends View> clazz = null;
 
        try {
            
            if (constructor == null) {
                // 通过反射创建class对象
                clazz = Class.forName(prefix != null ? (prefix + name) : name, false,
                        mContext.getClassLoader()).asSubclass(View.class);
 
                //创建构造函数  这里的mConstructorSignature 长这个样子
                //static final Class<?>[] mConstructorSignature = new Class[] {
                //        Context.class, AttributeSet.class};
                //看到了没 就是我们第二个构造方法
                constructor = clazz.getConstructor(mConstructorSignature);
                constructor.setAccessible(true);
                //缓存构造方法
                sConstructorMap.put(name, constructor);
            } else {
                ...
            }
 
            
            try {
                //执行构造函数 创建出view
                final View view = constructor.newInstance(args);
                ...
                return view;
            } finally {
                mConstructorArgs[0] = lastContext;
            }
        } catch (Exception e) {
            ...
        } finally {
            ...
        }
    }

override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
 
}

public static int getChildMeasureSpec(int spec, int padding, int childDimension) {
        
        //获取父类的尺寸模式
        int specMode = MeasureSpec.getMode(spec);
        //获取父类的尺寸大小
        int specSize = MeasureSpec.getSize(spec);
 
        //去掉padding后的大小 最小不能低于0
        int size = Math.max(0, specSize - padding);
 
        int resultSize = 0;
        int resultMode = 0;
 
        switch (specMode) {
        // 如果父类的模式是MeasureSpec.EXACTLY（精确模式，父类的值是可以确定的）
        case MeasureSpec.EXACTLY:
            if (childDimension >= 0) {
                //此时子view的大小就是我们设置的值，超过父类也没事，开发人员自定义设置的
                //比如父view的宽是100dp，子view宽你非要设置200dp，那就给200dp，这么做有什么
                //意义？这样是可以扩展的，不至于限制死，比如子view可能具有滚动属性或者其他高级 
                //玩法                
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.MATCH_PARENT) {
                // MATCH_PARENT 则子view和父view大小一致 模式是确定的
                resultSize = size;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                // WRAP_CONTENT 则子view和父view大小一致 模式是最大不超过这个值
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            }
            break;
 
        // Parent has imposed a maximum size on us
        case MeasureSpec.AT_MOST:
            if (childDimension >= 0) {
                // 按子view值执行，确定模式
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.MATCH_PARENT) {
                //按父view值执行 模式是最多不超过指定值模式
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                //按父view值执行 模式是最多不超过指定值模式
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            }
            break;
 
        // Parent asked to see how big we want to be
        case MeasureSpec.UNSPECIFIED:
            if (childDimension >= 0) {
                // 按子view值执行，确定模式
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.MATCH_PARENT) {
                // 按父view值执行 模式是未定义
                resultSize = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;
                resultMode = MeasureSpec.UNSPECIFIED;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                // 按父view值执行 模式是未定义
                resultSize = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;
                resultMode = MeasureSpec.UNSPECIFIED;
            }
            break;
        }
        //noinspection ResourceType
        return MeasureSpec.makeMeasureSpec(resultSize, resultMode);
    }

class ZSFlowLayout : ViewGroup {
 
    //保存所有子view 按行保存 每行都可能有多个view 所有是一个list
    var allViews: MutableList<MutableList<View>> = mutableListOf()
 
    //每个子view之间的水平间距
    val horizontalSpace: Int =
        resources.getDimensionPixelOffset(R.dimen.zs_flowlayout_horizontal_space)
 
    //每行之间的间距
    val verticalSpace: Int = resources.getDimensionPixelOffset(R.dimen.zs_flowlayout_vertical_space)
 
    //记录每一行的行高 onLayout时会用到
    var lineHeights: MutableList<Int> = mutableListOf()
 
    constructor(context: Context) : super(context) {}
 
    
    constructor(context: Context, attr: AttributeSet) : super(context, attr) {}
 
    constructor (context: Context, attr: AttributeSet, defZStyle: Int) : super(
        context,
        attr,
        defZStyle
    ) {
    }
 
    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        //会测量次
        allViews.clear()
        lineHeights.clear()
 
        //保存每一行的view
        var everyLineViews: MutableList<View> = mutableListOf()
        //记录每一行当前的宽度，用来判断是否要换行
        var curLineHasUsedWidth: Int = paddingLeft + paddingRight
        //父布局能给的宽
        val selfWidth: Int = MeasureSpec.getSize(widthMeasureSpec)
        //父布局能给的高
        val selfHeight: Int = MeasureSpec.getSize(heightMeasureSpec)
        //我们自己通过测量需要的宽（如果用户在布局里对ZSFlowLayout的宽设置了wrap_content 就会用到这个）
        var selfNeedWidth = 0
        //我们自己通过测量需要的高（如果用户在布局里对ZSFlowLayout的高设置了wrap_content 就会用到这个）
        var selfNeedHeight = paddingBottom + paddingTop
        var curLineHeight = 0
 
        //第一步 先测量子view 核心系统方法是 View measure方法
        //（1）因为子view有很多，所以循环遍历执行
        for (i in 0 until childCount) {
            val childView = getChildAt(i)
            if (childView.visibility == GoNE) {
                continue
            }
            //测量view之前 先把测量需要的参数准备好 通过ViewGroup getChildMeasureSpec获取子view的MeasureSpec信息
            val childWidthMeasureSpec = getChildMeasureSpec(
                widthMeasureSpec,
                paddingLeft + paddingRight,
                childView.layoutParams.width
            )
            val childHeightMeasureSpec = getChildMeasureSpec(
                heightMeasureSpec,
                paddingTop + paddingBottom,
                childView.layoutParams.height
            )
            //调用子view的measure方法来对子view进行测量
            childView.measure(childWidthMeasureSpec, childHeightMeasureSpec)
 
            //测量之后就能拿到子view的宽高了,保存起来用于判断是否要换行 以及需要的总高度
            val measuredHeight = childView.measuredHeight
            val measuredWidth = childView.measuredWidth
 
            //按行保存view 保存之前判断是否需要换行，如果需要就保存在下一行的list里面
            if (curLineHasUsedWidth + measuredWidth > selfWidth) {
                //要换行了 先记录换行之前的数据
                lineHeights.add(curLineHeight)
                selfNeedHeight += curLineHeight + verticalSpace
                allViews.add(everyLineViews)
 
                //再处理当前要换行的view相关数据
                curLineHeight = measuredHeight
                everyLineViews = mutableListOf()
                curLineHasUsedWidth = paddingLeft + paddingRight + measuredWidth + horizontalSpace
            } else {
                //每一行的高度是这一行view中最高的那个
                curLineHeight = curLineHeight.coerceAtLeast(measuredHeight)
                curLineHasUsedWidth += measuredWidth + horizontalSpace
            }
            everyLineViews.add(childView)
            selfNeedWidth = selfNeedWidth.coerceAtLeast(curLineHasUsedWidth)
 
            //处理最后一行
            if (i == childCount - 1) {
                curLineHeight = curLineHeight.coerceAtLeast(measuredHeight)
                allViews.add(everyLineViews)
                selfNeedHeight += curLineHeight
                lineHeights.add(curLineHeight)
            }
        }
 
        //第二步 测量自己
        //根据父类传入的尺寸规则 widthMeasureSpec、heightMeasureSpec 获取当前自身应该遵守的布局模式
        //以widthMeasureSpec为例说明下 这个是父类传入的，那父类是如何按照什么规则生成的widthMeasureSpec呢？
        //父类会结合自身的情况，并且结合子view的情况（子类的宽是match_parent、wrap_content、还是写死的值）来生成
        //生成的具体逻辑 请见：ViewGroup的getChildMeasureSpec方法
        //(1)获取父类传过来的 我们自身应该遵守的尺寸模式
        val widthMode = MeasureSpec.getMode(widthMeasureSpec)
        val heightMode = MeasureSpec.getMode(heightMeasureSpec)
        //(2)根据模式来判断最终的宽高
        val widthResult = if (widthMode == MeasureSpec.EXACTLY) selfWidth else selfNeedWidth
        val heightResult = if (heightMode == MeasureSpec.EXACTLY) selfHeight else selfNeedHeight
        //第三步 设置自身的测量结果
        setMeasuredDimension(widthResult, heightResult)
    }
 
    override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {
        //设置所有view的位置
        var curT = paddingTop
        for (i in allViews.indices) {
            val mutableList = allViews[i]
            //记录每一行view的当前距离父布局左侧的位置 初始值就是父布局的paddingLeft
            var curL = paddingLeft
            if (i != 0) {
                curT += lineHeights[i - 1] + verticalSpace
            }
            for (j in mutableList.indices) {
                val view = mutableList[j]
                val right = curL + view.measuredWidth
                val bottom = curT + view.measuredHeight
                view.layout(curL, curT, right, bottom)
                //为下一个view做准备
                curL += view.measuredWidth + horizontalSpace
            }
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="Http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
 
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
 
        <TextView
            android:layout_marginTop="10dp"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="@dimen/zs_flowlayout_title_marginL"
            android:text="三国名将"
            android:textColor="@android:color/black"
            android:textSize="18sp" />
 
        <com.zs.test.customview.ZSFlowLayout
            android:id="@+id/activity_flow_flowlayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="8dp"
            android:padding="7dp">
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="吕布吕奉先" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="赵云赵子龙" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:paddingLeft="10dp"
                android:text="典韦" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="关羽关云长" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="马超马孟起" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="张飞张翼德" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="黄忠" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="徐褚徐仲康" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="孙策孙伯符" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="太史慈" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="夏侯惇" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="夏侯渊" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="张辽" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="张郃" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="徐晃徐功明" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="庞德" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="甘宁甘兴霸" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="周泰" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="魏延" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="张绣" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="文丑" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="颜良" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="邓艾" />
 
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@drawable/shape_button_circular"
                android:text="姜维" />
 
        </com.zs.test.customview.ZSFlowLayout>
 
    </LinearLayout>
 
</ScrollView>

class FlowActivity : AppCompatActivity() {
 
    @BindView(id = R.id.activity_flow_flowlayout)
    var flowLayout : ZSFlowLayout ? = null;
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_customview_flow)
        BindViewInject.inject(this)
 
        for (i in 1 until 50) {
            val tv:TextView = TextView(this)
            tv.text = "TextView $i"
            flowLayout!!.addView(tv)
        }
    }
}

object BindViewInject {
 
 
    
    @JVMStatic
    fun inject(activity: Activity) {
        inject(activity, false)
    }
 
    fun inject(activity: Activity, isSetOnClickListener: Boolean) {
        //第一步 获取class对象
        val aClass: Class<out Activity> = activity.javaClass
        //第二步 获取类本身定义的所有成员变量
        val declaredFields = aClass.declaredFields
        //第三步 遍历找出有注解的属性
        for (i in declaredFields.indices) {
            val field = declaredFields[i]
            //判断是否用BindView进行注解
            if (field.isAnnotationPresent(BindView::class.java)) {
                //得到注解对象
                val bindView = field.getAnnotation(BindView::class.java)
                //得到注解对象上的id值 这个就是view的id
                val id = bindView.id
                if (id <= 0) {
                    Toast.makeText(activity, "请设置正确的id", Toast.LENGTH_LONG).show()
                    return
                }
                //建立映射关系，找出view
                val view = activity.findViewById<View>(id)
                //修改权限
                field.isAccessible = true
                //第四步 给属性赋值
                try {
                    field[activity] = view
                } catch (e: IllegalAccessException) {
                    e.printStackTrace()
                }
                //第五步 设置点击监听
                if (isSetOnClickListener) {
                    //这里用反射实现 增加练习
                    //第一步 获取这个属性的值
                    val button = field.get(activity)
                    //第二步 获取其class对象
                    val javaClass = button.javaClass
                    //第三步 获取其 setOnClickListener 方法
                    val method =
                        javaClass.getMethod("setOnClickListener", View.OnClickListener::class.java)
                    //第四步 执行此方法
                    method.invoke(button, activity)
                }
            }
        }
    }
}

@Target(AnnotationTarget.FIELD)
@Retention(RetentionPolicy.RUNTIME)
annotation class BindView( //value是默认的，如果只有一个参数，并且名称是value，外面传递时可以直接写值，否则就要通过键值对来传值（例如：value = 1）
    //    int value() default 0;
    val id: Int = 0
)