Android片段演示错误

Question

I'm working with Beginning Android 4 Application Development by Wei-Meng Lee and stuck in Chapter 2 where they introduce fragments. I have followed the demo code by the letter yet continue to have the application fail at runtime. Any workarounds I have found on the internet always produce the same error. Looking through the LogCat it appears the primary source is a java.lang.ClassNotFoundException and android.app.Fragment$InstantiationException

I have tried to use the the android.support.v4.app.Fragment as well as the android.support.v4.app.FragmentActivity and have my main activity extend it instead, but neither have provided a solution. I examined the build path and toyed around with it for a bit with no luck either. I have no idea why the program cannot find my classes as they are located in what I believe is the correct directory.

Here is the LogCat Error output:

04-20 14:10:35.572: E/AndroidRuntime(1114): FATAL EXCEPTION: main
04-20 14:10:35.572: E/AndroidRuntime(1114): Process: solaris.data.demofragment, PID: 1114
04-20 14:10:35.572: E/AndroidRuntime(1114): java.lang.RuntimeException: Unable to start       activity ComponentInfo{solaris.data.demofragment/solaris.data.demofragment.MainActivity}:  android.view.InflateException: Binary XML file line #7: Error inflating class fragment
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.os.Handler.dispatchMessage(Handler.java:102)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at  android.os.Looper.loop(Looper.java:136)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.app.ActivityThread.main(ActivityThread.java:5017)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at java.lang.reflect.Method.invokeNative(Native Method)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at java.lang.reflect.Method.invoke(Method.java:515)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at dalvik.system.NativeStart.main(Native Method)
04-20 14:10:35.572: E/AndroidRuntime(1114): Caused by: android.view.InflateException: Binary XML file line #7: Error inflating class fragment
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:713)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.view.LayoutInflater.rInflate(LayoutInflater.java:755)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.view.LayoutInflater.inflate(LayoutInflater.java:353)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:290)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.app.Activity.setContentView(Activity.java:1929)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at solaris.data.demofragment.MainActivity.onCreate(MainActivity.java:19)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.app.Activity.performCreate(Activity.java:5231)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
04-20 14:10:35.572: E/AndroidRuntime(1114):     ... 11 more
04-20 14:10:35.572: E/AndroidRuntime(1114): Caused by: android.app.Fragment$InstantiationException: Unable to instantiate fragment solaris.data.demofragment.fragment1: make sure class name exists, is public, and has an empty constructor that is public
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.app.Fragment.instantiate(Fragment.java:597)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.app.Fragment.instantiate(Fragment.java:561)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.app.Activity.onCreateView(Activity.java:4778)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:689)
04-20 14:10:35.572: E/AndroidRuntime(1114):     ... 21 more
04-20 14:10:35.572: E/AndroidRuntime(1114): Caused by: java.lang.ClassNotFoundException: Didn't find class "solaris.data.demofragment.fragment1" on path: DexPathList[[zip file "/data/app/solaris.data.demofragment-1.apk"],nativeLibraryDirectories=[/data/app-lib/solaris.data.demofragment-1, /system/lib]]
04-20 14:10:35.572: E/AndroidRuntime(1114):     at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at java.lang.ClassLoader.loadClass(ClassLoader.java:497)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at java.lang.ClassLoader.loadClass(ClassLoader.java:457)
04-20 14:10:35.572: E/AndroidRuntime(1114):     at android.app.Fragment.instantiate(Fragment.java:583)
04-20 14:10:35.572: E/AndroidRuntime(1114):     ... 24 more

Main activity:

package solaris.data.demofragment;

import android.app.Activity;
import android.app.ActionBar;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.os.Build;

public class MainActivity extends Activity {

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, 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);
    }

}

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal" >

<fragment
    android:name="solaris.data.demofragment.fragment1"
    android:id="@+id/fragment1"
    android:layout_weight="1"
    android:layout_width="0px"
    android:layout_height="match_parent" />
<fragment
    android:name="solaris.data.demofragment.fragment2"
    android:id="@+id/fragment2"
    android:layout_weight="1"
    android:layout_width="0px"
    android:layout_height="match_parent" />
</LinearLayout>

fragment1.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" 
android:background="#00FF00"
>
<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="This is fragment #1"
    android:textColor="#000000"
    android:textSize="25sp" />
</LinearLayout>

Fragment1.java

package solaris.data.demofragment;

import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class Fragment1 extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment1, container, false);
    }
}

Fragment2.java and fragment2.xml are identical to their respective 1 counterparts, except for name, the text displayed, and color. All .xml files are located in the res/layout folder, and all java files are located in the src/solaris.data.demofragment package. The min sdk-version is 14 with the target as 19.

Answer 1

The name attribute for your fragments that you defined in activity_main.xml are incorrect.

Instead of

android:name="solaris.data.demofragment.fragment1"

it should be

android:name="solaris.data.demofragment.Fragment1"

This is because they are case-sensitive as you defined it as

public class Fragment1 extends Fragment

So when android inflated your activity_main.xml , it could not find a fragment with the name of fragment1 . This will also apply to your fragment2 if the class is Fragment2 .