Android 自動換行的LinearLayout

時間 2019-11-12

標籤 android 自動換行 linearlayout 欄目 Android 简体版

原文原文鏈接

在咱們開發過程當中會常常碰見一些客戶要求可是Android系統又不提供的效果，這時咱們只能本身動手去實現它，或者從網絡上借鑑他人的資源，本着用別人不如本身會作的心態，在此我總結了一下Android中如何實現自動換行的LinearLayout。html

在本文中，說是LinearLayout實際上是繼承自GroupView，在這裏主要重寫了兩個方法，onMeasure、onLayout方法，下面我對此加以介紹。（代碼中使用了AttributeSet，因爲時間問題再也不予以介紹）。java

1. onMeasure是幹什麼的？

在ViewGroup的建立過程當中，onMeasure是在onLayout以前的，因此在此先對onMeasure進行介紹，onMeasure方法是計算子控件與父控件在屏幕中所佔長寬大小的，onMeasure傳入兩個參數——widthMeasureSpec和heightMeasureSpec. 這兩個參數指明控件可得到的空間以及關於這個空間描述的元數據.android

int withMode = MeasureSpec.getMode(widthMeasureSpec);
int withSize = MeasureSpec.getSize(widthMeasureSpec);
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);網絡

Mode有3種模式分別是UNSPECIFIED, EXACTLY和AT_MOST，若是是AT_MOST，Size表明的是最大可得到的空間；若是是EXACTLY，Size表明的是精確的尺寸；若是是UNSPECIFIED，就是你想要多少就有多少。通過代碼測試就知道，當咱們設置width或height爲fill_parent時，容器在佈局時調用子 view的measure方法傳入的模式是EXACTLY，由於子view會佔據剩餘容器的空間，因此它大小是肯定的。而當設置爲 wrap_content時，容器傳進去的是AT_MOST, 表示子view的大小最可能是多少，這樣子view會根據這個上限來設置本身的尺寸。當子view的大小設置爲精確值時，容器傳入的是EXACTLY。app

2. onLayout是幹什麼的？

與onMesaure相比，onLayout更加容易理解，它的做用就是調座位，就是把全部的子View根據不一樣的須要，經過View. layout(int l, int t, int r, int b)方法指定它所在的位置。dom

3. 解決問題

只要對onMeasure和onLayout加以理解，對於該篇所要實現的功能就再也不難以實現，下面貼上代碼，並在代碼中講解。ide

WaroLinearLayout.java佈局

[java] view plain copy測試

public class WarpLinearLayout extends ViewGroup {
private Type mType;
private List<WarpLine> mWarpLineGroup;
public WarpLinearLayout(Context context) {
this(context, null);
}
public WarpLinearLayout(Context context, AttributeSet attrs) {
this(context, attrs, R.style.WarpLinearLayoutDefault);
}
public WarpLinearLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
mType = new Type(context, attrs);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int withMode = MeasureSpec.getMode(widthMeasureSpec);
int withSize = MeasureSpec.getSize(widthMeasureSpec);
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
int with = 0;
int height = 0;
int childCount = getChildCount();
/**
* 在調用childView。getMeasre以前必須先調用該行代碼，用於對子View大小的測量
*/
measureChildren(widthMeasureSpec, heightMeasureSpec);
/**
* 計算寬度
*/
switch (withMode) {
case MeasureSpec.EXACTLY:
with = withSize;
break;
case MeasureSpec.AT_MOST:
for (int i = 0; i < childCount; i++) {
if (i != 0) {
with += mType.horizontal_Space;
}
with += getChildAt(i).getMeasuredWidth();
}
with += getPaddingLeft() + getPaddingRight();
with = with > withSize ? withSize : with;
break;
case MeasureSpec.UNSPECIFIED:
for (int i = 0; i < childCount; i++) {
if (i != 0) {
with += mType.horizontal_Space;
}
with += getChildAt(i).getMeasuredWidth();
}
with += getPaddingLeft() + getPaddingRight();
break;
default:
with = withSize;
break;
}
/**
* 根據計算出的寬度，計算出所須要的行數
*/
WarpLine warpLine = new WarpLine();
/**
* 不可以在定義屬性時初始化，由於onMeasure方法會屢次調用
*/
mWarpLineGroup = new ArrayList<WarpLine>();
for (int i = 0; i < childCount; i++) {
if (warpLine.lineWidth + getChildAt(i).getMeasuredWidth() + mType.horizontal_Space > with) {
if (warpLine.lineView.size() == 0) {
warpLine.addView(getChildAt(i));
mWarpLineGroup.add(warpLine);
warpLine = new WarpLine();
} else {
mWarpLineGroup.add(warpLine);
warpLine = new WarpLine();
warpLine.addView(getChildAt(i));
}
} else {
warpLine.addView(getChildAt(i));
}
}
/**
* 添加最後一行
*/
if (warpLine.lineView.size() > 0 && !mWarpLineGroup.contains(warpLine)) {
mWarpLineGroup.add(warpLine);
}
/**
* 計算寬度
*/
height = getPaddingTop() + getPaddingBottom();
for (int i = 0; i < mWarpLineGroup.size(); i++) {
if (i != 0) {
height += mType.vertical_Space;
}
height += mWarpLineGroup.get(i).height;
}
switch (heightMode) {
case MeasureSpec.EXACTLY:
height = heightSize;
break;
case MeasureSpec.AT_MOST:
height = height > heightSize ? heightSize : height;
break;
case MeasureSpec.UNSPECIFIED:
break;
default:
break;
}
setMeasuredDimension(with, height);
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
t = getPaddingTop();
for (int i = 0; i < mWarpLineGroup.size(); i++) {
int left = getPaddingLeft();
WarpLine warpLine = mWarpLineGroup.get(i);
int lastWidth = getMeasuredWidth() - warpLine.lineWidth;
for (int j = 0; j < warpLine.lineView.size(); j++) {
View view = warpLine.lineView.get(j);
if (isFull()) {//須要充滿當前行時
view.layout(left, t, left + view.getMeasuredWidth() + lastWidth / warpLine.lineView.size(), t + view.getMeasuredHeight());
left += view.getMeasuredWidth() + mType.horizontal_Space + lastWidth / warpLine.lineView.size();
} else {
switch (getGrivate()) {
case 0://右對齊
view.layout(left + lastWidth, t, left + lastWidth + view.getMeasuredWidth(), t + view.getMeasuredHeight());
break;
case 2://居中對齊
view.layout(left + lastWidth / 2, t, left + lastWidth / 2 + view.getMeasuredWidth(), t + view.getMeasuredHeight());
break;
default://左對齊
view.layout(left, t, left + view.getMeasuredWidth(), t + view.getMeasuredHeight());
break;
}
left += view.getMeasuredWidth() + mType.horizontal_Space;
}
}
t += warpLine.height + mType.vertical_Space;
}
}
/**
* 用於存放一行子View
*/
private final class WarpLine {
private List<View> lineView = new ArrayList<View>();
/**
* 當前行中所須要佔用的寬度
*/
private int lineWidth = getPaddingLeft() + getPaddingRight();
/**
* 該行View中所須要佔用的最大高度
*/
private int height = 0;
private void addView(View view) {
if (lineView.size() != 0) {
lineWidth += mType.horizontal_Space;
}
height = height > view.getMeasuredHeight() ? height : view.getMeasuredHeight();
lineWidth += view.getMeasuredWidth();
lineView.add(view);
}
}
/**
* 對樣式的初始化
*/
private final static class Type {
/*
*對齊方式 right 0，left 1，center 2
*/
private int grivate;
/**
* 水平間距,單位px
*/
private float horizontal_Space;
/**
* 垂直間距,單位px
*/
private float vertical_Space;
/**
* 是否自動填滿
*/
private boolean isFull;
Type(Context context, AttributeSet attrs) {
if (attrs == null) {
return;
}
TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.WarpLinearLayout);
grivate = typedArray.getInt(R.styleable.WarpLinearLayout_grivate, grivate);
horizontal_Space = typedArray.getDimension(R.styleable.WarpLinearLayout_horizontal_Space, horizontal_Space);
vertical_Space = typedArray.getDimension(R.styleable.WarpLinearLayout_vertical_Space, vertical_Space);
isFull = typedArray.getBoolean(R.styleable.WarpLinearLayout_isFull, isFull);
}
}
public int getGrivate() {
return mType.grivate;
}
public float getHorizontal_Space() {
return mType.horizontal_Space;
}
public float getVertical_Space() {
return mType.vertical_Space;
}
public boolean isFull() {
return mType.isFull;
}
public void setGrivate(int grivate) {
mType.grivate = grivate;
}
public void setHorizontal_Space(float horizontal_Space) {
mType.horizontal_Space = horizontal_Space;
}
public void setVertical_Space(float vertical_Space) {
mType.vertical_Space = vertical_Space;
}
public void setIsFull(boolean isFull) {
mType.isFull = isFull;
}
/**
* 每行子View的對齊方式
*/
public final static class Gravite {
public final static int RIGHT = 0;
public final static int LEFT = 1;
public final static int CENTER = 2;
}
}