Fragment使用时出现 java.lang.IllegalStateException_java.lang.illegalstateexception: fragment richtagh

Fragment使用时出现 java.lang.IllegalStateException

标签（空格分隔）： Android Fragment View

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在写侧栏滑动UI时，切换不同选项时，Fragment切换程序终止
报错：

java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
            at android.view.ViewGroup.addViewInner(ViewGroup.java:3880)
            at android.view.ViewGroup.addView(ViewGroup.java:3733)
            at android.view.ViewGroup.addView(ViewGroup.java:3678)
            at android.view.ViewGroup.addView(ViewGroup.java:3654)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:905)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
            at android.app.BackStackRecord.run(BackStackRecord.java:833)
            at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1452)
            at android.app.FragmentManagerImpl1.run(FragmentManager.java:447)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5466)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:938)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:733)
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错误原因便是：

java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child’s parent first

出现此错误的根本问题是当前VIEW已经在别的View中，作为别的子View，而你现在又要将当前VIEW放在别的View中，就会抛出这类错误信息。解决方法是是先找到当前VIEW的父VIEW，在父VIEW中调用removeView(),移除当前VIEW，就可以解决此问题了.

此时Fragment代码如下：

public class ChooseAreaFragment extends Fragment{
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){

        View view = inflater.inflate(R.layout.choose_area,container);

        listView = (ListView) view.findViewById(R.id.list_view);
        titleText = (TextView) view.findViewById(R.id.title_text);
        adapter = new ArrayAdapter<>(getActivity(), android.R.layout.simple_list_item_1,dataList);
        listView.setAdapter(adapter);
        myWeatherDB = MyWeatherDB.getInstance(getActivity());
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                if (currentLevel == LEVEL_PROVINCE) {
                    selectProvince = provinceList.get(position);
                    queryCities();
                } else if (currentLevel == LEVEL_CITY) {
                    selectCity = cityList.get(position);
                    queryCounties();
                }
            }
        });
        Log.d("xyz onCreateView","true");
        queryProvinces();
        return view;
    }
}
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网络上找到一个解决方案：

View view = inflater.inflate(R.layout.choose_area,container);
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改为

View view = inflater.inflate(R.layout.choose_area,container,false);
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实际测试解决了这个问题。
原理是怎么样的呢，false是什么作用？

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查看API源码：

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();
        }
    }
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这里调用了另一个方法
查看API源码：

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
        synchronized (mConstructorArgs) {
            Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");

            final Context inflaterContext = mContext;
            final AttributeSet attrs = Xml.asAttributeSet(parser);
            Context lastContext = (Context) mConstructorArgs[0];
            mConstructorArgs[0] = inflaterContext;
            View result = root;

            try {
                // Look for the root node.
                int type;
                while ((type = parser.next()) != XmlPullParser.START_TAG &&
                        type != XmlPullParser.END_DOCUMENT) {
                    // Empty
                }

                if (type != XmlPullParser.START_TAG) {
                    throw new InflateException(parser.getPositionDescription()
                            + ": No start tag found!");
                }

                final String name = parser.getName();

                if (DEBUG) {
                    System.out.println("**************************");
                    System.out.println("Creating root view: "
                            + name);
                    System.out.println("**************************");
                }

                if (TAG_MERGE.equals(name)) {
                    if (root == null || !attachToRoot) {
                        throw new InflateException("<merge /> can be used only with a valid "
                                + "ViewGroup root and attachToRoot=true");
                    }

                    rInflate(parser, root, inflaterContext, attrs, false);
                } else {
                    // Temp is the root view that was found in the xml
                    final View temp = createViewFromTag(root, name, inflaterContext, attrs);

                    ViewGroup.LayoutParams params = null;

                    if (root != null) {
                        if (DEBUG) {
                            System.out.println("Creating params from root: " +
                                    root);
                        }
                        // Create layout params that match root, if supplied
                        params = root.generateLayoutParams(attrs);
                        if (!attachToRoot) {
                            // Set the layout params for temp if we are not
                            // attaching. (If we are, we use addView, below)
                            temp.setLayoutParams(params);
                        }
                    }

                    if (DEBUG) {
                        System.out.println("-----> start inflating children");
                    }

                    // Inflate all children under temp against its context.
                    rInflateChildren(parser, temp, attrs, true);

                    if (DEBUG) {
                        System.out.println("-----> done inflating children");
                    }

                    // We are supposed to attach all the views we found (int temp)
                    // to root. Do that now.
                    if (root != null && attachToRoot) {
                        root.addView(temp, params);
                    }

                    // Decide whether to return the root that was passed in or the
                    // top view found in xml.
                    if (root == null || !attachToRoot) {
                        result = temp;
                    }
                }

            } catch (XmlPullParserException e) {
                InflateException ex = new InflateException(e.getMessage());
                ex.initCause(e);
                throw ex;
            } catch (Exception e) {
                InflateException ex = new InflateException(
                        parser.getPositionDescription()
                                + ": " + e.getMessage());
                ex.initCause(e);
                throw ex;
            } finally {
                // Don't retain static reference on context.
                mConstructorArgs[0] = lastContext;
                mConstructorArgs[1] = null;
            }

            Trace.traceEnd(Trace.TRACE_TAG_VIEW);

            return result;
        }
    }
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直接看核心部分的代码：

if (root != null) {
    if (DEBUG) {
        System.out.println("Creating params from root: " +
                root);
    }
    // Create layout params that match root, if supplied
    params = root.generateLayoutParams(attrs);
    if (!attachToRoot) {
        // Set the layout params for temp if we are not
        // attaching. (If we are, we use addView, below)
        temp.setLayoutParams(params);
    }
}
...
// We are supposed to attach all the views we found (int temp)
// to root. Do that now.
if (root != null && attachToRoot) {
    root.addView(temp, params);
}

// Decide whether to return the root that was passed in or the
// top view found in xml.
if (root == null || !attachToRoot) {
    result = temp;
}
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个人理解是设置了false该方法就没有把这个View添加的root中，使用了一个临时变量（temp翻译的，感觉好理解）。测试了一下如果不用false就会出现这个错误。应该是在Fragment被使用前，该View已经被加载进root里了。