Android百分比支持布局库的使用和源码分析

Android-percent-support这个库

描述下这个support-lib。

这个库提供了：

  • 两种布局供大家使用：
    PercentRelativeLayout、PercentFrameLayout，通过名字就可以看出，这是继承自FrameLayout和RelativeLayout两个容器类；

  • 支持的属性有：

　　layout_widthPercent、layout_heightPercent、
　　layout_marginPercent、layout_marginLeftPercent、
　　layout_marginTopPercent、layout_marginRightPercent、
　　layout_marginBottomPercent、layout_marginStartPercent、layout_marginEndPercent。

　　可以看到支持宽高，以及margin。

　　也就是说，大家只要在开发过程中使用PercentRelativeLayout、PercentFrameLayout替换FrameLayout、RelativeLayout即可。

　　过没有LinearLayout，有人会说LinearLayout有weight属性呀。但是，weight属性只能支持一个方向,但可以去自定义一个PercentLinearLayout。

使用

关于使用，其实及其简单，并且github上也有例子，android-percent-support-lib-sample

build.gradle添加：

compile 'com.android.support:percent:22.2.0'

（一）PercentFrameLayout

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<?xml version="1.0" encoding="utf-8"?>
<android.support.percent.PercentFrameLayout
    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:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.loaderman.percentsupportdemo.MainActivity">
 
    <TextView
        android:id="@+id/tv1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#ff0000"
        android:gravity="center"
        android:text="高10%"
        android:textColor="#ffffff"
        app:layout_heightPercent="10%"
        app:layout_widthPercent="10%"/>
 
    <TextView
        android:id="@+id/tv2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#00ff00"
        android:gravity="center"
        android:text="高20%"
        android:textColor="#ffffff"
        app:layout_heightPercent="20%"
        app:layout_marginLeftPercent="10%"
        app:layout_marginTopPercent="10%"
        app:layout_widthPercent="20%"/>
 
    <TextView
        android:id="@+id/tv3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#0000ff"
        android:gravity="center"
        android:text="高30%"
        android:textColor="#ffffff"
        app:layout_heightPercent="30%"
        app:layout_marginLeftPercent="30%"
        app:layout_marginTopPercent="30%"
        app:layout_widthPercent="30%"/>
 
    <TextView
        android:id="@+id/tv4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#3f5500"
        android:gravity="center"
        android:text="高40%"
        android:textColor="#ffffff"
        app:layout_heightPercent="40%"
        app:layout_marginLeftPercent="60%"
        app:layout_marginTopPercent="60%"
        app:layout_widthPercent="40%"/>
 
</android.support.percent.PercentFrameLayout>

 效果图:

(二) PercentRelativeLayout

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<?xml version="1.0" encoding="utf-8"?>
<android.support.percent.PercentRelativeLayout
    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:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.loaderman.percentsupportdemo.MainActivity">
 
    <TextView
        android:id="@+id/tv1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#ff0000"
        android:gravity="center"
        android:layout_alignParentBottom="true"
        android:text="高10%"
        android:textColor="#ffffff"
        app:layout_heightPercent="10%"
        app:layout_widthPercent="10%"/>
 
    <TextView
        android:id="@+id/tv2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#00ff00"
        android:gravity="center"
        android:layout_alignParentBottom="true"
        android:text="高20%"
        android:textColor="#ffffff"
        app:layout_heightPercent="20%"
        app:layout_marginLeftPercent="10%"
        app:layout_marginTopPercent="10%"
        app:layout_widthPercent="20%"/>
 
    <TextView
        android:id="@+id/tv3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#0000ff"
        android:gravity="center"
        android:text="高30%"
        android:textColor="#ffffff"
        android:layout_alignParentBottom="true"
        app:layout_heightPercent="30%"
        app:layout_marginLeftPercent="30%"
        app:layout_marginTopPercent="30%"
        app:layout_widthPercent="30%"/>
 
    <TextView
        android:id="@+id/tv4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#3f5500"
        android:gravity="center"
        android:text="高40%"
        android:layout_alignParentBottom="true"
        android:textColor="#ffffff"
        app:layout_heightPercent="40%"
        app:layout_marginLeftPercent="60%"
        app:layout_marginTopPercent="60%"
        app:layout_widthPercent="40%"/>
 
</android.support.percent.PercentRelativeLayout>

 效果图:

(三)、实现PercentLinearlayout

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package com.loaderman.percentsupportdemo;
 
import android.content.Context;
import android.content.res.TypedArray;
import android.support.percent.PercentLayoutHelper;
import android.util.AttributeSet;
import android.view.ViewGroup;
import android.widget.LinearLayout;
 
/**
 * Created by JCF on 2017/2/27.
 */
 
public class PercentLinearLayout extends LinearLayout {
    private PercentLayoutHelper mPercentLayoutHelper;
 
    public PercentLinearLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
 
        mPercentLayoutHelper = new PercentLayoutHelper(this);
    }
 
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        mPercentLayoutHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (mPercentLayoutHelper.handleMeasuredStateTooSmall()) {
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        }
    }
 
    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        mPercentLayoutHelper.restoreOriginalParams();
    }
 
    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new LayoutParams(getContext(), attrs);
    }
 
 
    public static class LayoutParams extends LinearLayout.LayoutParams
            implements PercentLayoutHelper.PercentLayoutParams {
        private PercentLayoutHelper.PercentLayoutInfo mPercentLayoutInfo;
 
        public LayoutParams(Context c, AttributeSet attrs) {
            super(c, attrs);
            mPercentLayoutInfo = PercentLayoutHelper.getPercentLayoutInfo(c, attrs);
        }
 
        @Override
        public PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo() {
            return mPercentLayoutInfo;
        }
 
        @Override
        protected void setBaseAttributes(TypedArray a, int widthAttr, int heightAttr) {
            PercentLayoutHelper.fetchWidthAndHeight(this, a, widthAttr, heightAttr);
        }
 
        public LayoutParams(int width, int height) {
            super(width, height);
        }
 
 
        public LayoutParams(ViewGroup.LayoutParams source) {
            super(source);
        }
 
        public LayoutParams(MarginLayoutParams source) {
            super(source);
        }
 
    }
 
}

 布局测试:

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<?xml version="1.0" encoding="utf-8"?>
<com.loaderman.percentsupportdemo.PercentLinearLayout
    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:orientation="vertical">
 
    <TextView
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="#ff44aacc"
        android:text="width:60%,height:5%"
        android:textColor="#ffffff"
        app:layout_heightPercent="5%"
        app:layout_marginBottomPercent="5%"
        app:layout_widthPercent="60%"/>
 
    <TextView
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="#ff4400cc"
        android:gravity="center"
        android:textColor="#ffffff"
        android:text="width:70%,height:10%"
        app:layout_heightPercent="10%"
        app:layout_marginBottomPercent="5%"
        app:layout_widthPercent="70%"/>
    <TextView
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="#ff44aacc"
        android:gravity="center"
        android:text="width:80%,height:15%"
        android:textColor="#ffffff"
        app:layout_heightPercent="15%"
        app:layout_marginBottomPercent="5%"
        app:layout_widthPercent="80%"/>
    <TextView
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="#ff4400cc"
        android:gravity="center"
        android:text="width:90%,height:5%"
        android:textColor="#ffffff"
        app:layout_heightPercent="20%"
        app:layout_marginBottomPercent="10%"
        app:layout_widthPercent="90%"/>
 
    <TextView
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:background="#ff44aacc"
        android:gravity="center"
        android:text="width:100%,height:25%"
        android:textColor="#ffffff"
        app:layout_heightPercent="25%"
        app:layout_marginBottomPercent="5%"
        />
 
</com.loaderman.percentsupportdemo.PercentLinearLayout>

 效果图:

源码分析

其实细想一下，Google只是对我们原本熟悉的RelativeLayout和FrameLayout进行的功能的扩展，使其支持了percent相关的属性。

那么，我们考虑下，如果是我们添加这种扩展，我们会怎么做：

  • 通过LayoutParams获取child设置的percent相关属性的值
  • onMeasure的时候，将child的width,height的值，通过获取的自定义属性的值进行计算（eg:容器的宽 * fraction ），计算后传入给child.measure(w,h);

ok，有了上面的猜想，我们直接看PercentFrameLayout的源码。

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public class PercentFrameLayout extends FrameLayout {
    private final PercentLayoutHelper mHelper = new PercentLayoutHelper(this);
 
    //省略了，两个构造方法
 
    public PercentFrameLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
 
 
 
    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new LayoutParams(getContext(), attrs);
    }
 
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        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 FrameLayout.LayoutParams
            implements PercentLayoutHelper.PercentLayoutParams {
        private PercentLayoutHelper.PercentLayoutInfo mPercentLayoutInfo;
 
        public LayoutParams(Context c, AttributeSet attrs) {
            super(c, attrs);
            mPercentLayoutInfo = PercentLayoutHelper.getPercentLayoutInfo(c, attrs);
        }
        //省略了一些代码...
 
        @Override
        public PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo() {
            return mPercentLayoutInfo;
        }
 
        @Override
        protected void setBaseAttributes(TypedArray a, int widthAttr, int heightAttr) {
            PercentLayoutHelper.fetchWidthAndHeight(this, a, widthAttr, heightAttr);
        }
    }
}

 代码是相当的短，可以看到PercentFrameLayout里面首先重写了generateLayoutParams方法，当然了，由于支持了一些新的layout_属性，那么肯定需要定义对应的LayoutParams。

（一）percent相关属性的获取

可以看到PercentFrameLayout.LayoutParams在原有的FrameLayout.LayoutParams基础上，实现了PercentLayoutHelper.PercentLayoutParams接口。

这个接口很简单，只有一个方法：

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public interface PercentLayoutParams {
        PercentLayoutInfo getPercentLayoutInfo();
}

 而，这个方法的实现呢，也只有一行：return mPercentLayoutInfo;，那么这个mPercentLayoutInfo在哪完成赋值呢？

看PercentFrameLayout.LayoutParams的构造方法：

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public LayoutParams(Context c, AttributeSet attrs) {
    super(c, attrs);
    mPercentLayoutInfo = PercentLayoutHelper.getPercentLayoutInfo(c, attrs);
}

 可以看到，将attrs传入给getPercentLayoutInfo方法，那么不用说，这个方法的内部，肯定是获取自定义属性的值，然后将其封装到PercentLayoutInfo对象中，最后返回。代码如下：

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public static PercentLayoutInfo getPercentLayoutInfo(Context context,
            AttributeSet attrs) {
        PercentLayoutInfo info = null;
        TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.PercentLayout_Layout);
        float value = array.getFraction(R.styleable.PercentLayout_Layout_layout_widthPercent, 1, 1,
                -1f);
        if (value != -1f) {
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                Log.v(TAG, "percent width: " + value);
            }
            info = info != null ? info : new PercentLayoutInfo();
            info.widthPercent = value;
        }
        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_heightPercent, 1, 1, -1f);
        if (value != -1f) {
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                Log.v(TAG, "percent height: " + value);
            }
            info = info != null ? info : new PercentLayoutInfo();
            info.heightPercent = value;
        }
        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginPercent, 1, 1, -1f);
        if (value != -1f) {
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                Log.v(TAG, "percent margin: " + value);
            }
            info = info != null ? info : new PercentLayoutInfo();
            info.leftMarginPercent = value;
            info.topMarginPercent = value;
            info.rightMarginPercent = value;
            info.bottomMarginPercent = value;
        }
        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginLeftPercent, 1, 1,
                -1f);
        if (value != -1f) {
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                Log.v(TAG, "percent left margin: " + value);
            }
            info = info != null ? info : new PercentLayoutInfo();
            info.leftMarginPercent = value;
        }
        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginTopPercent, 1, 1,
                -1f);
        if (value != -1f) {
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                Log.v(TAG, "percent top margin: " + value);
            }
            info = info != null ? info : new PercentLayoutInfo();
            info.topMarginPercent = value;
        }
        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginRightPercent, 1, 1,
                -1f);
        if (value != -1f) {
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                Log.v(TAG, "percent right margin: " + value);
            }
            info = info != null ? info : new PercentLayoutInfo();
            info.rightMarginPercent = value;
        }
        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginBottomPercent, 1, 1,
                -1f);
        if (value != -1f) {
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                Log.v(TAG, "percent bottom margin: " + value);
            }
            info = info != null ? info : new PercentLayoutInfo();
            info.bottomMarginPercent = value;
        }
        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginStartPercent, 1, 1,
                -1f);
        if (value != -1f) {
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                Log.v(TAG, "percent start margin: " + value);
            }
            info = info != null ? info : new PercentLayoutInfo();
            info.startMarginPercent = value;
        }
        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginEndPercent, 1, 1,
                -1f);
        if (value != -1f) {
            if (Log.isLoggable(TAG, Log.VERBOSE)) {
                Log.v(TAG, "percent end margin: " + value);
            }
            info = info != null ? info : new PercentLayoutInfo();
            info.endMarginPercent = value;
        }
        array.recycle();
        if (Log.isLoggable(TAG, Log.DEBUG)) {
            Log.d(TAG, "constructed: " + info);
        }
        return info;
    }

 

是不是和我们平时的取值很类似，所有的值最终封装到PercentLayoutInfo对象中。

ok，到此我们的属性获取就介绍完成，有了这些属性，是不是onMeasure里面要进行使用呢？

(二) onMeasue中重新计算child的尺寸

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@Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (mHelper.handleMeasuredStateTooSmall()) {
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        }
    }

 可以看到onMeasure中的代码页很少，看来核心的代码都被封装在mHelper的方法中，我们直接看mHelper.adjustChildren方法。

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/**
     * Iterates over children and changes their width and height to one calculated from percentage
     * values.
     * @param widthMeasureSpec Width MeasureSpec of the parent ViewGroup.
     * @param heightMeasureSpec Height MeasureSpec of the parent ViewGroup.
     */
    public void adjustChildren(int widthMeasureSpec, int heightMeasureSpec) {
        //...
        int widthHint = View.MeasureSpec.getSize(widthMeasureSpec);
        int heightHint = View.MeasureSpec.getSize(heightMeasureSpec);
        for (int i = 0, N = mHost.getChildCount(); i < N; i++) {
            View view = mHost.getChildAt(i);
            ViewGroup.LayoutParams params = view.getLayoutParams();
 
            if (params instanceof PercentLayoutParams) {
                PercentLayoutInfo info =
                        ((PercentLayoutParams) params).getPercentLayoutInfo();
                if (Log.isLoggable(TAG, Log.DEBUG)) {
                    Log.d(TAG, "using " + info);
                }
                if (info != null) {
                    if (params instanceof ViewGroup.MarginLayoutParams) {
                        info.fillMarginLayoutParams((ViewGroup.MarginLayoutParams) params,
                                widthHint, heightHint);
                    } else {
                        info.fillLayoutParams(params, widthHint, heightHint);
                    }
                }
            }
        }
    }

 

通过注释也能看出，此方法中遍历所有的孩子，通过百分比的属性重新设置其宽度和高度。

首先在widthHint、heightHint保存容器的宽、高，然后遍历所有的孩子，判断其LayoutParams是否是PercentLayoutParams类型，如果是，通过params.getPercentLayoutInfo拿出info对象。

是否还记得，上面的分析中，PercentLayoutInfo保存了percent相关属性的值。

如果info不为null，则判断是否需要处理margin；我们直接看fillLayoutParams方法（处理margin也是类似的）。

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/**
         * Fills {@code ViewGroup.LayoutParams} dimensions based on percentage values.
         */
        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;
 
            if (widthPercent >= 0) {
                params.width = (int) (widthHint * widthPercent);
            }
            if (heightPercent >= 0) {
                params.height = (int) (heightHint * heightPercent);
            }
            if (Log.isLoggable(TAG, Log.DEBUG)) {
                Log.d(TAG, "after fillLayoutParams: (" + params.width + ", " + params.height + ")");
            }
        }

 

首先保存原本的width和height，然后重置params的width和height为(int) (widthHint * widthPercent)和(int) (heightHint * heightPercent);。

到此，其实我们的百分比转换就结束了，理论上就已经实现了对于百分比的支持，不过Google还考虑了一些细节。

我们回到onMeasure方法：

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@Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (mHelper.handleMeasuredStateTooSmall()) {
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        }
    }

 下面还有个mHelper.handleMeasuredStateTooSmall的判断，也就是说，如果你设置的百分比，最终计算出来的MeasuredSize过小的话，会进行一些操作。代码如下：

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public boolean handleMeasuredStateTooSmall() {
        boolean needsSecondMeasure = false;
        for (int i = 0, N = mHost.getChildCount(); i < N; i++) {
            View view = mHost.getChildAt(i);
            ViewGroup.LayoutParams params = view.getLayoutParams();
            if (Log.isLoggable(TAG, Log.DEBUG)) {
                Log.d(TAG, "should handle measured state too small " + view + " " + params);
            }
            if (params instanceof PercentLayoutParams) {
                PercentLayoutInfo info =
                        ((PercentLayoutParams) params).getPercentLayoutInfo();
                if (info != null) {
                    if (shouldHandleMeasuredWidthTooSmall(view, info)) {
                        needsSecondMeasure = true;
                        params.width = ViewGroup.LayoutParams.WRAP_CONTENT;
                    }
                    if (shouldHandleMeasuredHeightTooSmall(view, info)) {
                        needsSecondMeasure = true;
                        params.height = ViewGroup.LayoutParams.WRAP_CONTENT;
                    }
                }
            }
        }
        if (Log.isLoggable(TAG, Log.DEBUG)) {
            Log.d(TAG, "should trigger second measure pass: " + needsSecondMeasure);
        }
        return needsSecondMeasure;
    }

 首先遍历所有的孩子，拿出孩子的layoutparams，如果是PercentLayoutParams实例，则取出info。如果info不为null，调用shouldHandleMeasuredWidthTooSmall判断：

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private static boolean shouldHandleMeasuredWidthTooSmall(View view, PercentLayoutInfo info) {
        int state = ViewCompat.getMeasuredWidthAndState(view) & ViewCompat.MEASURED_STATE_MASK;
        return state == ViewCompat.MEASURED_STATE_TOO_SMALL && info.widthPercent >= 0 &&
                info.mPreservedParams.width == ViewGroup.LayoutParams.WRAP_CONTENT;
}

 

这里就是判断，如果你设置的measuredWidth或者measureHeight过小的话，并且你在布局文件中layout_w/h 设置的是WRAP_CONTENT的话，将params.width / height= ViewGroup.LayoutParams.WRAP_CONTENT，然后重新测量。

哈，onMeasure终于结束了~~~现在我觉得应该代码结束了吧，尺寸都设置好了，还需要干嘛么，but，你会发现onLayout也重写了，我们又不改变layout规则，在onLayout里面干什么毛线：

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@Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        mHelper.restoreOriginalParams();
    }

 继续看mHelper.restoreOriginalParams

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/**
     * Iterates over children and restores their original dimensions that were changed for
     * percentage values. Calling this method only makes sense if you previously called
     * {@link PercentLayoutHelper#adjustChildren(int, int)}.
     */
    public void restoreOriginalParams() {
        for (int i = 0, N = mHost.getChildCount(); i < N; i++) {
            View view = mHost.getChildAt(i);
            ViewGroup.LayoutParams params = view.getLayoutParams();
            if (Log.isLoggable(TAG, Log.DEBUG)) {
                Log.d(TAG, "should restore " + view + " " + params);
            }
            if (params instanceof PercentLayoutParams) {
                PercentLayoutInfo info =
                        ((PercentLayoutParams) params).getPercentLayoutInfo();
                if (Log.isLoggable(TAG, Log.DEBUG)) {
                    Log.d(TAG, "using " + info);
                }
                if (info != null) {
                    if (params instanceof ViewGroup.MarginLayoutParams) {
                        info.restoreMarginLayoutParams((ViewGroup.MarginLayoutParams) params);
                    } else {
                        info.restoreLayoutParams(params);
                    }
                }
            }
        }
    }

 噗，原来是重新恢复原本的尺寸值，也就是说onMeasure里面的对值进行了改变，测量完成后。在这个地方，将值又恢复成如果布局文件中的值，上面写的都是0。恢复很简单：

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public void restoreLayoutParams(ViewGroup.LayoutParams params) {
            params.width = mPreservedParams.width;
            params.height = mPreservedParams.height;
        }

 你应该没有忘在哪存的把~忘了的话，麻烦Ctrl+F ‘mPreservedParams.width’ 。

也就是说，你去打印上面写法，布局文件中view的v.getLayoutParams().width，这个值应该是0。

这里感觉略微不爽~这个0没撒用处呀，还不如不重置~~

好了，到此就分析完了，其实主要就几个步骤：

  • LayoutParams中属性的获取
  • onMeasure中，改变params.width为百分比计算结果，测量
  • 如果测量值过小且设置的w/h是wrap_content，重新测量
  • onLayout中，重置params.w/h为布局文件中编写的值

可以看到，有了RelativeLayout、FrameLayout的扩展，竟然没有LinearLayout几个意思。好在，我们的核心代码都由PercentLayoutHelper封装了，自己扩展下LinearLayout也不复杂。

 

本文学习来源:http://blog.csdn.net/lmj623565791/article/details/46695347

 

posted on   LoaderMan  阅读(751)  评论(0)  编辑  收藏  举报

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