未找到片段 id 0x 的视图

Question

我遵循 The Big Nerd Ranch 的“Android 编程”一书中的指导方针。当我在手机上运行应用程序时，它说“应用程序已意外停止。再试一次”。这是它在 LogCat 中显示的第一行：

10-21 10:11:48.550: E/FragmentManager(6393): No view found for id 0x7f05003c (com.bignerdranch.android.criminalIntent:id/fragmentContainer) for fragment CrimeFragment{4054c7d0 #0 id=0x7f05003c}
10-21 10:11:48.550: E/FragmentManager(6393): Activity state:

这是我有 fragmentContainer 的地方：

package com.bignerdranch.android.criminalIntent;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;


public class CrimeActivity extends ActionBarActivity {
	//Call when the activity is first created
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_crime);
        
        android.support.v4.app.FragmentManager fm = getSupportFragmentManager();
        Fragment fragment = fm.findFragmentById(R.id.fragmentContainer);
        
        if (fragment == null){ 
        	fragment = new CrimeFragment();
        	fm.beginTransaction()
        	.add(R.id.fragmentContainer, fragment)
        	.commit();
        } //Create a new fragment transaction, include one add operation in it, and then commit it
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.crime, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

这是 .xml 文件。当 fragmentContainer 无法解析时，我添加了这一行 android:id="@+id/fragmentContainer"

<?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="match_parent"
    android:orientation="vertical"
    android:id="@+id/fragmentContainer" >
    <EditText android:id="@+id/crime_title"
        
        android:layout_width ="match_parent"
        android:layout_height = 'wrap_content'
        android:hint = "@string/crime_title_hint"
         />
    

</LinearLayout>

这里是清单以及其余的 java 和 xml 文件：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.bignerdranch.android.criminalIntent"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="21" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".CrimeActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

CrimeFragment.java

package com.bignerdranch.android.criminalIntent;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;

public class CrimeFragment extends Fragment {
	private Crime mCrime;
	private EditText mTitleField;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		// TODO Auto-generated method stub
		super.onCreate(savedInstanceState);
		mCrime = new Crime();
	}

	@Override
	public View onCreateView(LayoutInflater inflater,
			@Nullable ViewGroup parent, @Nullable Bundle savedInstanceState) {
		// inflates fragment_crime.xml
		//onCreateView method is also the place to wire up the EditText to respond to user input
		View v = inflater.inflate(R.layout.fragment_crime, parent, false);
		mTitleField = (EditText)v.findViewById(R.id.crime_title);
		mTitleField.addTextChangedListener(new TextWatcher(){
			public void onTextChanged(
					CharSequence c, int start, int before, int count){
				mCrime.setTitle(c.toString()); //set title, CharSequence is user's input
			}
			public void beforeTextChanged(CharSequence c, int start, int count, int after){
				
			}
			public void afterTextChanged(Editable c){
				
			}
		});
		return v;
	}
	
	


}

犯罪.java

package com.bignerdranch.android.criminalIntent;

import java.util.UUID;

public class Crime {
	private UUID mId;
	private String mTitle;
	
	public Crime()  {
		//Generate unique identifier
		mId = UUID.randomUUID();
	}

	public String getTitle() {
		return mTitle;
	}

	public void setTitle(String title) {
		mTitle = title;
	}

	public UUID getId() {
		return mId;
	}
}

分别在 res/layout 中的fragment_crime.xml 和activity_crime.xml：

<RelativeLayout 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: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="com.bignerdranch.android.criminalIntent.CrimeActivity" >


</RelativeLayout>

<?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="match_parent"
    android:orientation="vertical"
    android:id="@+id/fragmentContainer" >
    <EditText android:id="@+id/crime_title"
        
        android:layout_width ="match_parent"
        android:layout_height = 'wrap_content'
        android:hint = "@string/crime_title_hint"
         />
    

</LinearLayout>

res/menu 中的crime.xml：

<menu 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"
    tools:context="com.bignerdranch.android.criminalIntent.CrimeActivity" >

    <item
        android:id="@+id/action_settings"
        android:orderInCategory="100"
        app:showAsAction="never"/>

</menu>

我对 Android 应用程序开发非常陌生，因此非常感谢每一个意见。谢谢！

Answer 1

所以我会以这种方式简化 onCreate()。容器检查不需要它自己的具体对象，它的引用类型是 LinearLayout 而不是 Fragment。此外，在您知道自己将需要它之前，即在 null 检查之后，您不希望调用片段管理器。

public class CrimeActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_crime);

         if (findViewById(R.id.fragmentContainer != null) {
             CrimeFragment fragment = new CrimeFragment();
             getSupportFragmentManager().beginTransaction()
                     .add(R.id.fragmentContainer, fragment).commit();
         }
    }

请试试这个。