AndroidLinearLayout实现自动换行效果

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。

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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 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();
    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 lineView = new ArrayList();
    /**
     * 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"?>

WarpLinearLayoutDefault

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"?>

运行效果图如下：

Android LinearLayout实现自动换行效果

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AndroidLinearLayout实现自动换行效果

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