在 Android 中使用 Fragment 时出现 ClassCastException

Question

我最近在自学android。我按照我的教科书尝试使用片段但是即使我输入的代码与我的课本完全一样，我还是遇到了错误。

你们能给我解释一下哪里出了问题吗？

这是MainActivity.java

package com.example.ex_1;

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    public static class CounterFragment extends Fragment {

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            // TODO Auto-generated method stub

            View root = inflater.inflate(R.layout.counterfragment, container, false);
            Button btnIncrease = (Button)root.findViewById(R.id.btnincrease);
            final TextView textCounter = (TextView)root.findViewById(R.id.txtcounter);
            btnIncrease.setOnClickListener(new Button.OnClickListener() {
                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    int count = Integer.parseInt(textCounter.getText().toString());
                    textCounter.setText(Integer.toString(count + 1));
                }

            });
            return root;
        }

    }
}

这是activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/LinearLayout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="${relativePackage}.${activityClass}" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="~~"/>
    <fragment 
        android:name="com.example.ex_1.MainActivity$CounterFragment"
        android:id="@+id/counterfragment"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

错误是

09-24 07:40:08.329: E/AndroidRuntime(1794): FATAL EXCEPTION: main
09-24 07:40:08.329: E/AndroidRuntime(1794): Process: com.example.ex_1, PID: 1794
09-24 07:40:08.329: E/AndroidRuntime(1794): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ex_1/com.example.ex_1.MainActivity}: android.view.InflateException: Binary XML file line #13: Error inflating class fragment
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.ActivityThread.access0(ActivityThread.java:144)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.os.Handler.dispatchMessage(Handler.java:102)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.os.Looper.loop(Looper.java:135)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.ActivityThread.main(ActivityThread.java:5221)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at java.lang.reflect.Method.invoke(Native Method)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at java.lang.reflect.Method.invoke(Method.java:372)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
09-24 07:40:08.329: E/AndroidRuntime(1794): Caused by: android.view.InflateException: Binary XML file line #13: Error inflating class fragment
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:763)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.view.LayoutInflater.rInflate(LayoutInflater.java:806)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.view.LayoutInflater.inflate(LayoutInflater.java:504)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.view.LayoutInflater.inflate(LayoutInflater.java:414)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.view.LayoutInflater.inflate(LayoutInflater.java:365)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:377)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.Activity.setContentView(Activity.java:2144)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at com.example.ex_1.MainActivity.onCreate(MainActivity.java:19)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.Activity.performCreate(Activity.java:5937)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
09-24 07:40:08.329: E/AndroidRuntime(1794):     ... 10 more
09-24 07:40:08.329: E/AndroidRuntime(1794): Caused by: android.app.Fragment$InstantiationException: Trying to instantiate a class com.example.ex_1.MainActivity$CounterFragment that is not a Fragment
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.Fragment.instantiate(Fragment.java:606)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.Fragment.instantiate(Fragment.java:582)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2108)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.Activity.onCreateView(Activity.java:5286)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:733)
09-24 07:40:08.329: E/AndroidRuntime(1794):     ... 20 more
09-24 07:40:08.329: E/AndroidRuntime(1794): Caused by: java.lang.ClassCastException
09-24 07:40:08.329: E/AndroidRuntime(1794):     ... 25 more

Answer 1

问题是您将 api 级别设置得太低，因此它使用 "support" 版本的片段，而不是 "base" 片段

将 "min api level" 放在你的 androidmanifest 中的 11，删除对 "support" 库的依赖，删除 "import android.support.v4.app.Fragment" 并将其替换为 "import android.app.fragment" 它应该可以工作

Answer 2

改变

public class MainActivity extends Activity {

到

public class MainActivity extends FragmentActivity {

在 Android 中使用 Fragment 时出现 ClassCastException

ClassCastException when using Fragment in Android

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classcastexception