Android 自动换行的LinearLayout

在我们开发过程中会经常遇见一些客户要求但是Android系统又不提供的效果，这时我们只能自己动手去实现它，或者从网络上借鉴他人的资源，本着用别人不如自己会做的心态，在此我总结了一下Android中如何实现自动换行的LinearLayout。

在本文中，说是LinearLayout其实是继承自GroupView，在这里主要重写了两个方法，onMeasure、onLayout方法，下面我对此加以介绍。（代码中使用了AttributeSet，由于时间问题不再予以介绍）。

1. onMeasure是干什么的？

在ViewGroup的创建过程中，onMeasure是在onLayout之前的，所以在此先对onMeasure进行介绍，onMeasure方法是计算子控件与父控件在屏幕中所占长宽大小的，onMeasure传入两个参数——widthMeasureSpec和heightMeasureSpec. 这两个参数指明控件可获得的空间以及关于这个空间描述的元数据.

int withMode = MeasureSpec.getMode(widthMeasureSpec);

int withSize = MeasureSpec.getSize(widthMeasureSpec);

int heightMode = MeasureSpec.getMode(heightMeasureSpec);

int heightSize = MeasureSpec.getSize(heightMeasureSpec);
Mode有3种模式分别是UNSPECIFIED, EXACTLY和AT_MOST，如果是AT_MOST，Size代表的是最大可获得的空间；如果是EXACTLY，Size代表的是精确的尺寸；如果是UNSPECIFIED，就是你想要多少就有多少。经过代码测试就知道，当我们设置width或height为fill_parent时，容器在布局时调用子 view的measure方法传入的模式是EXACTLY，因为子view会占据剩余容器的空间，所以它大小是确定的。而当设置为 wrap_content时，容器传进去的是AT_MOST,
表示子view的大小最多是多少，这样子view会根据这个上限来设置自己的尺寸。当子view的大小设置为精确值时，容器传入的是EXACTLY。

2. onLayout是干什么的？

与onMesaure相比，onLayout更加容易理解，它的作用就是调座位，就是把所有的子View根据不同的需要，通过View. layout(int l, int t, int r, int b)方法指定它所在的位置。

3. 解决问题

只要对onMeasure和onLayout加以理解，对于该篇所要实现的功能就不再难以实现，下面贴上代码，并在代码中讲解。

WaroLinearLayout.java

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();
/**
* 在调用childView。getMeasre之前必须先调用该行代码，用于对子View大小的测量
*/
measureChildren(widthMeasureSpec, heightMeasureSpec);
/**
* 计算宽度
*/
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;

}
/**
* 根据计算出的宽度，计算出所需要的行数
*/
WarpLine warpLine = new WarpLine();
/**
* 不能够在定义属性时初始化，因为onMeasure方法会多次调用
*/
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));
}
}
/**
* 添加最后一行
*/
if (warpLine.lineView.size() > 0 && !mWarpLineGroup.contains(warpLine)) {
mWarpLineGroup.add(warpLine);
}
/**
* 计算宽度
*/
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()) {//需要充满当前行时
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://右对齐
view.layout(left + lastWidth, t, left + lastWidth + view.getMeasuredWidth(), t + view.getMeasuredHeight());
break;
case 2://居中对齐
view.layout(left + lastWidth / 2, t, left + lastWidth / 2 + view.getMeasuredWidth(), t + view.getMeasuredHeight());
break;
default://左对齐
view.layout(left, t, left + view.getMeasuredWidth(), t + view.getMeasuredHeight());
break;
}
left += view.getMeasuredWidth() + mType.horizontal_Space;
}
}
t += warpLine.height + mType.vertical_Space;
}
}

/**
* 用于存放一行子View
*/
private final class WarpLine {
private List<View> lineView = new ArrayList<View>();
/**
* 当前行中所需要占用的宽度
*/
private int lineWidth = getPaddingLeft() + getPaddingRight();
/**
* 该行View中所需要占用的最大高度
*/
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);
}
}

/**
* 对样式的初始化
*/
private final static class Type {
/*
*对齐方式 right 0，left 1，center 2
*/
private int grivate;
/**
* 水平间距,单位px
*/
private float horizontal_Space;
/**
* 垂直间距,单位px
*/
private float vertical_Space;
/**
* 是否自动填满
*/
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的对齐方式
*/
public final static class Gravite {
public final static int RIGHT = 0;
public final static int LEFT = 1;
public final static int CENTER = 2;
}
}

attrs.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="WarpLinearLayout">
<attr name="grivate" format="enum"><!--对齐方式 !-->
<enum name="right" value="0"></enum>
<enum name="left" value="1"></enum>
<enum name="center" value="2"></enum>
</attr>
<attr name="horizontal_Space" format="dimension"></attr>
<attr name="vertical_Space" format="dimension"></attr>
<attr name="isFull" format="boolean"></attr>
</declare-styleable>
</resources>

WarpLinearLayoutDefault

<style name="WarpLinearLayoutDefault">
<item name="grivate">left</item>
<item name="horizontal_Space">20dp</item>
<item name="vertical_Space">20dp</item>
<item name="isFull">false</item>
</style>

MainActivity.java

public class MainActivity extends Activity {
private Button btn;
private WarpLinearLayout warpLinearLayout;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn = (Button) findViewById(R.id.btn);
warpLinearLayout = (WarpLinearLayout) findViewById(R.id.warpLinearLayout);
btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
int n = new Random().nextInt(10) + 5;
StringBuffer stringBuffer = new StringBuffer();
Random random = new Random();
Log.i("WarpLinearLayout","n="+n);
for (int i = 0; i < n; i++) {
stringBuffer.append((char)(65+random.nextInt(26)));
Log.i("WarpLinearLayout", "StringBuffer=" + stringBuffer.toString());
}
TextView tv = new TextView(MainActivity.this);
tv.setText(stringBuffer.toString()+"000");
tv.setBackgroundResource(R.drawable.radius_backgroup_yellow);
tv.setPadding(10,10,10,10);
warpLinearLayout.addView(tv);
}
});
}
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity">

<Button
android:id="@+id/btn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:text="add"
android:textSize="20dp" />

<com.example.customview.viewgroup.WarpLinearLayout
android:id="@+id/warpLinearLayout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@id/btn"
android:background="#FF00FF00"
android:padding="10dp"
app:grivate="right"
app:horizontal_Space="10dp"
app:isFull="false"
app:vertical_Space="10dp"></com.example.customview.viewgroup.WarpLinearLayout>
</RelativeLayout>

运行效果图如下：