在我們開發過程中會經常遇見一些客戶要求但是Android系統又不提供的效果，這時我們只能自己動手去實現它，或者從網絡上借鑒他人的資源，本著用別人不如自己會做的心態，在此我總結了一下Android中如何實現自動換行的LinearLayout。

在本文中，說是LinearLayout其實是繼承自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，由於時間問題不再予以介紹）。

1. onMeasure是幹什麽的？

在ViewGroup的創建過程中，onMeasure是在onLayout之前的，所以在此先對onMeasure進行介紹，onMeasure方法是計算子控件與父控件在屏幕中所占長寬大小的，onMeasure傳入兩個參數——widthMeasureSpec和heightMeasureSpec. 這兩個參數指明控件可獲得的空間以及關於這個空間描述的元數據.

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

Mode有3種模式分別是UNSPECIFIED, EXACTLY和AT_MOST，如果是AT_MOST，Size代表的是最大可獲得的空間；如果是EXACTLY，Size代表的是精確的尺寸；如果是UNSPECIFIED，就是你想要多少就有多少。經過代碼測試就知道，當我們設置width或height為fill_parent時，容器在布局時調用子 view的measure方法傳入的模式是EXACTLY，因為子view會占據剩余容器的空間，所以它大小是確定的。而當設置為 wrap_content時，容器傳進去的是AT_MOST, 表示子view的大小最多是多少，這樣子view會根據這個上限來設置自己的尺寸。當子view的大小設置為精確值時，容器傳入的是EXACTLY。

2. onLayout是幹什麽的？

與onMesaure相比，onLayout更加容易理解，它的作用就是調座位，就是把所有的子View根據不同的需要，通過View. layout(int l, int t, int r, int b)方法指定它所在的位置。

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不再難以實現，下面貼上代碼，並在代碼中講解。

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();
        /**
         * 在調用childView。getMeasre之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，計算出所需要的行數
         */
        WarpLine warpLine = new WarpLine();
        /**
         * 不能夠在定義屬性時初始化，因為onMeasure方法會多次調用
         */
        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()) {//需要充滿當前行時
                    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>();
        /**
         * 當前行中所需要占用的寬度
         */
        private int lineWidth = getPaddingLeft() + getPaddingRight();
        /**
         * 該行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);
        }
    }
 
    /**
     * 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;
    }
}

attrs.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="WarpLinearLayout">
        <attr name="grivate" format="enum"><!--對齊方式 !-->
            <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>

運行效果圖如下：

Android 自動換行的LinearLayout