AndroidLinearLayout實現(xiàn)自動換行效果

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

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在本文中，說是LinearLayout其實是繼承自GroupView，在這里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，由于時間問題不再予以介紹）。

1. onMeasure是干什么的？

在ViewGroup的創(chuàng)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(shù)——widthMeasureSpec和heightMeasureSpec. 這兩個參數(shù)指明控件可獲得的空間以及關于這個空間描述的元數(shù)據(jù).

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(jīng)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(diào)用子 view的measure方法傳入的模式是EXACTLY，因為子view會占據(jù)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(jù)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是干什么的？

與onMesaure相比，onLayout更加容易理解，它的作用就是調(diào)座位，就是把所有的子View根據(jù)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，對于該篇所要實現(xiàn)的功能就不再難以實現(xiàn)，下面貼上代碼，并在代碼中講解。

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(diào)用childView。getMeasre之前必須先調(diào)用該行代碼，用于對子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(jù)計算出的寬度，計算出所需要的行數(shù)
     */
    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(diào)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);
    }
    /**
     * 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;
    }
  }
 
  /**
   * 用于存放一行子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 LinearLayout實現(xiàn)自動換行效果

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