Android 百分比布局详解及实例代码

public class PercentRelativeLayout extends RelativeLayout {  private final PercentLayoutHelper mHelper = new PercentLayoutHelper(this);  /**省略若干行构造方法之类的代码**/  @Override  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {    //重点在这    mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);    super.onMeasure(widthMeasureSpec, heightMeasureSpec);    if (mHelper.handleMeasuredStateTooSmall()) {      super.onMeasure(widthMeasureSpec, heightMeasureSpec);    }  }  @Override  protected void onLayout(boolean changed, int left, int top, int right, int bottom) {    super.onLayout(changed, left, top, right, bottom);    mHelper.restoreOriginalParams();  }  public static class LayoutParams extends RelativeLayout.LayoutParams      implements PercentLayoutHelper.PercentLayoutParams {    private PercentLayoutHelper.PercentLayoutInfo mPercentLayoutInfo;    public LayoutParams(Context c, AttributeSet attrs) {      super(c, attrs);      mPercentLayoutInfo = PercentLayoutHelper.getPercentLayoutInfo(c, attrs);    }     /**省略若干行构造方法之类的代码**/    @Override    public PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo() {      if (mPercentLayoutInfo == null) {        mPercentLayoutInfo = new PercentLayoutHelper.PercentLayoutInfo();      }      return mPercentLayoutInfo;    }    @Override    protected void setBaseAttributes(TypedArray a, int widthAttr, int heightAttr) {      PercentLayoutHelper.fetchWidthAndHeight(this, a, widthAttr, heightAttr);    }  }}

public void adjustChildren(int widthMeasureSpec, int heightMeasureSpec) {    // Calculate available space, accounting for host's paddings    int widthHint = View.MeasureSpec.getSize(widthMeasureSpec) - mHost.getPaddingLeft()        - mHost.getPaddingRight();    int heightHint = View.MeasureSpec.getSize(heightMeasureSpec) - mHost.getPaddingTop()        - mHost.getPaddingBottom();    for (int i = 0, N = mHost.getChildCount(); i < N; i++) {      //遍历子view来设置 子view的宽高      View view = mHost.getChildAt(i);      ViewGroup.LayoutParams params = view.getLayoutParams();      if (DEBUG) {        Log.d(TAG, "should adjust " + view + " " + params);      }      if (params instanceof PercentLayoutParams) {        PercentLayoutInfo info =            ((PercentLayoutParams) params).getPercentLayoutInfo();        if (info != null) {          if (params instanceof ViewGroup.MarginLayoutParams) {            info.fillMarginLayoutParams(view, (ViewGroup.MarginLayoutParams) params,                widthHint, heightHint);          } else {            info.fillLayoutParams(params, widthHint, heightHint);          }        }      }    }  }

<android.support.percent.PercentRelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"  xmlns:app="http://schemas.android.com/apk/res-auto"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:background="@color/background_color"  >  <TextView    android:id="@+id/mian_tab_name"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:gravity="center"    android:textColor="@color/back_green"    android:textSize="15sp"    android:text="name"    />  <ImageView    app:layout_widthPercent="50%"    app:layout_heightPercent="50%"    android:src="@drawable/ic_launcher_icon"    android:scaleType="fitXY"    android:layout_below="@+id/mian_tab_name"    android:background="@color/black"    /></android.support.percent.PercentRelativeLayout>

<ImageView    app:layout_widthPercent="50%"    app:layout_aspectRatio="100%"    android:src="@drawable/ic_launcher_icon"    android:scaleType="fitXY"    android:layout_below="@+id/mian_tab_name"    android:background="@color/CS_black"    />

public void fillLayoutParams(ViewGroup.LayoutParams params, int widthHint,        int heightHint) {      // Preserve the original layout params, so we can restore them after the measure step.      mPreservedParams.width = params.width;      mPreservedParams.height = params.height;      // We assume that width/height set to 0 means that value was unset. This might not      // necessarily be true, as the user might explicitly set it to 0. However, we use this      // information only for the aspect ratio. If the user set the aspect ratio attribute,      // it means they accept or soon discover that it will be disregarded.      final boolean widthNotSet =          (mPreservedParams.mIsWidthComputedFromAspectRatio              || mPreservedParams.width == 0) && (widthPercent < 0);      final boolean heightNotSet =          (mPreservedParams.mIsHeightComputedFromAspectRatio              || mPreservedParams.height == 0) && (heightPercent < 0);      if (widthPercent >= 0) {        params.width = (int) (widthHint * widthPercent);      }      if (heightPercent >= 0) {        params.height = (int) (heightHint * heightPercent);      }      //这一段代码是关键，如果aspectRatio >=0，aspectRatio是宽高比      if (aspectRatio >= 0) {        if (widthNotSet) {           //如果宽没有设置，就以高为准          params.width = (int) (params.height * aspectRatio);          // Keep track that we've filled the width based on the height and aspect ratio.          mPreservedParams.mIsWidthComputedFromAspectRatio = true;        }        if (heightNotSet) {          //如果高没有设置，就以宽为准          params.height = (int) (params.width / aspectRatio);          // Keep track that we've filled the height based on the width and aspect ratio.          mPreservedParams.mIsHeightComputedFromAspectRatio = true;        }      }      if (DEBUG) {        Log.d(TAG, "after fillLayoutParams: (" + params.width + ", " + params.height + ")");      }    }