如何实现动态添加布局文件(避免 The specified child already has a parent的问题)
来源:互联网 发布:淘宝自动收获几天 编辑:程序博客网 时间:2024/06/13 10:45
首先扯点别的:我应经连续上了两个星期的班了,今天星期一。是第三个周。这个班上的也是没谁了。最近老是腰疼。估计是累了。最近也没跑步。今天下班继续跑起。
这篇文章讲一讲如何在一个布局文件中动态加在一个布局文件。避免出现The specified child already has a parent. You must call removeView() on the child’s parent first.的问题。先看一看效果再说。
接下来是实现过程 首先是 activity_add_view.xml文件
<?xml version="1.0" encoding="utf-8"?><android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:fitsSystemWindows="true" tools:context="com.example.administrator.learnaddview.AddViewActivity"><!--我们要在LinearLayout里面动态添加布局 现在这个LinearLayout里面只有三个textView--> <LinearLayout android:id="@+id/linearLayout" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center_horizontal" android:layout_marginTop="30dp" android:orientation="vertical"> <TextView android:id="@+id/textView1" android:layout_width="match_parent" android:layout_height="wrap_content" android:gravity="center" android:text="textView1" android:textSize="30dp" /> <TextView android:id="@+id/textView2" android:layout_width="match_parent" android:layout_height="wrap_content" android:gravity="center" android:text="textView2" android:textSize="30dp" /> <TextView android:id="@+id/textView3" android:layout_width="match_parent" android:layout_height="wrap_content" android:gravity="center" android:text="textView3" android:textSize="30dp" /> </LinearLayout><!--一个按钮用来添加布局--> <android.support.design.widget.FloatingActionButton android:id="@+id/fab" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="bottom|end" android:layout_margin="@dimen/fab_margin" android:src="@android:drawable/ic_input_add" /></android.support.design.widget.CoordinatorLayout>
然后是AddViewActivity.java代码
package com.example.administrator.learnaddview;import android.os.Bundle;import android.support.design.widget.FloatingActionButton;import android.support.v7.app.AppCompatActivity;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.ImageButton;import android.widget.TextView;public class AddViewActivity extends AppCompatActivity { private ViewGroup parentViewGroup;//父布局 /** * A static list of country names. */ private static final String[] COUNTRIES = new String[]{ "Belgium", "France", "Italy", "Germany", "Spain", "Austria", "Russia", "Poland", "Croatia", "Greece", "Ukraine", }; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_add_view); //找到想动态添加子view的布局容器就是上面布局中的LinearLayout parentViewGroup = (ViewGroup) findViewById(R.id.linearLayout); //找到浮动按钮并添加监听事件 FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); if (fab != null) { fab.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { //要被添加的子布局 final ViewGroup childViewGroup = (ViewGroup) LayoutInflater.from(AddViewActivity.this).inflate(R.layout.beaddlayout, parentViewGroup, false); //子布局中的TextView控件 TextView textView = (TextView) childViewGroup.findViewById(R.id.text1); //给textview随机设置一个文本 textView.setText(COUNTRIES[(int) (Math.random() * COUNTRIES.length)]); //子布局中的ImageButton控件 ImageButton imageButton= (ImageButton) childViewGroup.findViewById(R.id.delete_button); //给imageButton设置监听事件,当点击的时候就把这个刚添加的子布局从其父布局中删除掉 imageButton.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { parentViewGroup.removeView(childViewGroup); } }); parentViewGroup.addView(childViewGroup); } }); } }}
上面的beaddlayout.xml文件
<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="?android:listPreferredItemHeightSmall" android:divider="?android:dividerVertical" android:dividerPadding="8dp" android:gravity="center" android:orientation="horizontal" android:showDividers="middle"> <!-- 随机显示一个字符串 --> <TextView android:id="@+id/text1" style="?android:textAppearanceMedium" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:paddingLeft="?android:listPreferredItemPaddingLeft" /> <!-- 当按钮点击的时候会把这个布局文件从其父布局中移除--> <ImageButton android:id="@+id/delete_button" android:layout_width="48dp" android:layout_height="match_parent" android:background="?android:selectableItemBackground" android:contentDescription="remove" android:src="@drawable/ic_list_remove" /></LinearLayout>
下面来仔细讲解一下实现步骤
1,找到想添加布局的父布局
//找到想动态添加子view的布局容器就是上面布局中的LinearLayout parentViewGroup = (ViewGroup) findViewById(R.id.linearLayout);
2过滤将要被添加的布局文件到父布局中,父布局就是第一步骤中的parentViewGroup
//要被添加的子布局 /*inflate方法有三个参数 第一个参数:R.layout.beaddlayout 要被加载的布局 第二个参数:parentViewGroup 要被加载到那里 第三个参数:取值有true和false两种,等会我们试一试取值为true的情况*/ final ViewGroup childViewGroup = (ViewGroup) LayoutInflater.from(AddViewActivity.this).inflate(R.layout.beaddlayout, parentViewGroup, false);
3:这一步是可选的。通过childViewGroup找到其中的iew,并添加监听事件等等操作。
/*子布局中的TextView控件*/ TextView textView = (TextView) childViewGroup.findViewById(R.id.text1); textView.setText(COUNTRIES[(int) (Math.random() * COUNTRIES.length)]); //子布局中的ImageButton控件 ImageButton imageButton= (ImageButton)childViewGroup.findViewById(R.id.delete_button); //给imageButton设置监听事件,当点击的时候就把这个刚添加的子布局从其父布局中删除掉 imageButton.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { //parentViewGroup.removeView(childViewGroup); parentViewGroup.removeView(childViewGroup); } });
4:把子布局添加到父布局中。大功告成。
parentViewGroup.addView(childViewGroup);
在上面的第二步中
/*如果把最后一个参数取值为true,调用addView()的时候就会出现 the specified child already has a parent ,you must call the removeView() ....的问题*/final ViewGroup childViewGroup = (ViewGroup)//第三个参数取值为true LayoutInflater.from(AddViewActivity.this).inflate(R.layout.beaddlayout, parentViewGroup, true);
我们进入addView()方法,经过辗转反侧,我们会进入一个方法叫 addViewInner(child, index, params, false);异常就是在这里抛出的。但是这个child.getParent() != null我是真的不是很理解。
我的一个尝试性的理解是这样的
- 当LayoutInflater.from(AddViewActivity.this).inflate(R.layout.beaddlayout, parentViewGroup, true);//第三个参数取值为true的时候,这个方法返回childViewGroup 是在我们的R.layout.beaddlayout外层套上一层布局(就是我们本来打算加入的布局parentViewGroup)的布局。
- 取值为false的时候就直接返回我们的R.layout.beaddlayout。
- 所以当我们调用addView()方法方法的时候,由于我们的子布局已经套在parentViewGroup里面了。我们调用child.getParent() 得到的就是一个LinaerLayout(我们的父布局parentViewGroup).不为空,所以这时候,就会抛出一个异常。
private void addViewInner(View child, int index, LayoutParams params, boolean preventRequestLayout) { ......//省略前面的代码 if (child.getParent() != null) { throw new IllegalStateException("The specified child already has a parent. " + "You must call removeView() on the child's parent first."); } ....//省略后面的代码}
关于这个取值为true或者false的问题解释,我在网上找了很多说明,也没整明白,看了看这个方法的源码也还是难以理解,所以我把这个方法的源码贴出来,大家自己推敲一下。
/** * Inflate a new view hierarchy from the specified xml resource. Throws * {@link InflateException} if there is an error. * * @param resource ID for an XML layout resource to load (e.g., * <code>R.layout.main_page</code>) * @param root Optional view to be the parent of the generated hierarchy (if * <em>attachToRoot</em> is true), or else simply an object that * provides a set of LayoutParams values for root of the returned * hierarchy (if <em>attachToRoot</em> is false.) * @param attachToRoot Whether the inflated hierarchy should be attached to * the root parameter? If false, root is only used to create the * correct subclass of LayoutParams for the root view in the XML. * @return The root View of the inflated hierarchy. If root was supplied and * attachToRoot is true, this is root; otherwise it is the root of * the inflated XML file. */ public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) { final Resources res = getContext().getResources(); if (DEBUG) { Log.d(TAG, "INFLATING from resource: \"" + res.getResourceName(resource) + "\" (" + Integer.toHexString(resource) + ")"); } final XmlResourceParser parser = res.getLayout(resource); try { return inflate(parser, root, attachToRoot); } finally { parser.close(); } }
在第四步中,我们使用的是 parentViewGroup.addView(childViewGroup);来添加布局。这个方法还有其他几个重载的方法。如下
/*index 参数用来指出在父布局中的什么位置添加这个子view,取值是有讲究的。*/ addView(View child, int index); /* 这个方法可以用来明确指出子view的宽高*/ addView(View child, int width, int height); /*给子布局明确提供一个布局参数*/ addView(View child, LayoutParams params); /*给子view提供位置信息,和布局参数*/ addView(View child, int index, LayoutParams params)
接下来说一说addView(View child, int index);这个方法余下的几个方法就不说了。
在代码中我们把 parentViewGroup.addView(childViewGroup);改成 parentViewGroup.addView(childViewGroup,0);看一看有什么效果。
我们发现子布局被动态添加到了父布局的上面。
我们再改成 parentViewGroup.addView(childViewGroup,1);看一看有什么效果。
我们再改成 parentViewGroup.addView(childViewGroup,3);看一看有什么效果。
我们再改成 parentViewGroup.addView(childViewGroup,4);看一看有什么效果。
不用看了,当我们点击按钮的时候,程序直接崩溃了。我们看一看Log
java.lang.IndexOutOfBoundsException: index=4 count=3
at android.view.ViewGroup.addInArray(ViewGroup.java:3653)
at android.view.ViewGroup.addViewInner(ViewGroup.java:3584)
at android.view.ViewGroup.addView(ViewGroup.java:3415)
at android.view.ViewGroup.addView(ViewGroup.java:3360)
看到这里我想大家也许明白了点什么。我们的父布局LinearLayout中,原本只有三个TextView控件。我们index从0到2.当绘制子view的时候从0到index。而因为我们直接把index设为了4。我们这时父布局中只有4个view,从0到3,所以当遍历到4的时候就出现数组越界。
贴一下ViewGroup.java 3653的代码
/** * By default, children are clipped to their bounds before drawing. This * allows view groups to override this behavior for animations, etc. * * @param clipChildren true to clip children to their bounds, * false otherwise * @attr ref android.R.styleable#ViewGroup_clipChildren */ public void setClipChildren(boolean clipChildren) { boolean previousValue = (mGroupFlags & FLAG_CLIP_CHILDREN) == FLAG_CLIP_CHILDREN; if (clipChildren != previousValue) { setBooleanFlag(FLAG_CLIP_CHILDREN, clipChildren); for (int i = 0; i < mChildrenCount; ++i) { //这是3653行,我怀疑数组越界肯定和mChildrenCount有必然的联系。继续寻找原因。 View child = getChildAt(i); if (child.mRenderNode != null) { child.mRenderNode.setClipToBounds(clipChildren); } } invalidate(true); } }
1:我们进入addView(View child, int index)的源码找一找这个mChildrenCount在哪里。
public void addView(View child, int index) { if (child == null) { throw new IllegalArgumentException("Cannot add a null child view to a ViewGroup"); } LayoutParams params = child.getLayoutParams(); if (params == null) { //得到默认的布局参数,这个是父布局的布局参数 params = generateDefaultLayoutParams(); if (params == null) { throw new IllegalArgumentException("generateDefaultLayoutParams() cannot return null"); } } //看着一行,调用这个方法添加view,并使用一个默认的布局params参数 addView(child, index, params); }
2 我们接着跳进addView(child, index, params);源码
public void addView(View child, int index, LayoutParams params) { if (DBG) { System.out.println(this + " addView"); } if (child == null) { throw new IllegalArgumentException("Cannot add a null child view to a ViewGroup"); } // addViewInner() will call child.requestLayout() when setting the new LayoutParams // therefore, we call requestLayout() on ourselves before, so that the child's request // will be blocked at our level requestLayout(); invalidate(true); //注意这一行,我们继续跟踪 addViewInner(child, index, params, false); }
3进入addViewInner(child, index, params, false);方法,这个方法有点长,其中有一行代码太显眼了
addInArray(child, index);
4.我们继续跳入这个方法
private void addInArray(View child, int index) { View[] children = mChildren; final int count = mChildrenCount;//把mChildrenCount赋给count final int size = children.length; //如果index==count if (index == count) { if (size == count) { mChildren = new View[size + ARRAY_CAPACITY_INCREMENT]; System.arraycopy(children, 0, mChildren, 0, size); children = mChildren; } children[mChildrenCount++] = child; } //如果index<count else if (index < count) { if (size == count) { mChildren = new View[size + ARRAY_CAPACITY_INCREMENT]; System.arraycopy(children, 0, mChildren, 0, index); System.arraycopy(children, index, mChildren, index + 1, count - index); children = mChildren; } else { System.arraycopy(children, index, children, index + 1, count - index); } children[index] = child; mChildrenCount++; if (mLastTouchDownIndex >= index) { mLastTouchDownIndex++; } } //这个else也是没谁了,就是这里了。 else { throw new IndexOutOfBoundsException("index=" + index + " count=" + count); } }
源码中定义的mChildrenCount是代表mChildren数组的长度,也就是当前布局中view的个数
// Child views of this ViewGroup private View[] mChildren; // Number of valid children in the mChildren array, the rest should be null or not // considered as children private int mChildrenCount;
这个追踪也是欠妥,但是大家应该大致明白了是怎么回事,有兴趣的可以自己看看ViewGroup的源码自己找一找。
结尾:我的文章写得比较菜,欢迎大家提出疑问和指出错误。行,歇一歇,喝杯水。
- 如何实现动态添加布局文件(避免 The specified child already has a parent的问题)
- The specified child already has a parent.
- The specified child already has a parent
- The specified child already has a parent
- The specified child already has a parent
- Fragment error:The specified child already has a parent.
- The specified child already has a parent错误
- IllegalStateException: The specified child already has a parent问题解决办法
- The specified child already has a parent错误
- AlertDialog异常The specified child already has a parent. ..解决方法
- The specified child already has a parent错误解决办法
- ViewPager Fragment IllegalStateException: The specified child already has a parent
- The specified child already has a parent..."错误
- IllegalStateException :the specified child already has a parent
- IllegalStateException: The specified child already has a parent问题解决办法
- java.lang.IllegalStateException: The specified child already has a parent.
- Android The specified child already has a parent.解决方法
- IllegalStateException: The specified child already has a parent.
- 在下拉列表框里显示datastore里的服务内容
- 栈和堆
- iOS- 微信授权登录
- 剑指offer之面试题10:二进制中1的个数
- HDU1176 免费馅饼 DP
- 如何实现动态添加布局文件(避免 The specified child already has a parent的问题)
- Conversion to Dalvik format failed with error 1
- 数据截取的问题
- Jquery基础初探
- php连接sqlserver数据库服务器(或者称mssql数据库)的几种方法
- http://netfilter.org/ 读后感
- 图片文件上传以及图片文件流上传
- 原码补码反码以及位运算符
- Java使用极小的内存完成对超大数据的去重计数,用于实时计算中统计UV