java - 如果我尝试在 Activity 中打开 fragment ，应用程序会崩溃

Question

每次我尝试打开 MainActivity.class 中的 fragment 时，我的应用程序都会崩溃。

MainActivity.class

/* Menu */
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case R.id.add_server:
            Intent intent = new Intent(getApplicationContext(), AddServerFragment.class);
            startActivity(intent);
            return true;
        case R.id.menu_refresh:
            myWebView.reload();
            return true;
        default:
            return true;
    }        
...
 public class AddServerFragment extends Fragment {

    public AddServerFragment(){

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState){
        View rootView = inflater.inflate(R.layout.add_ip, container, false);

        Button btn_back, btn_add;
        final EditText server_ip, server_name;

        server_ip = (EditText) findViewById(R.id.edit_server_address);
        server_name = (EditText) findViewById(R.id.edit_server_name);

         /* Back Button */
        btn_back = (Button) findViewById(R.id.btn_back);
        btn_back.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {
                Intent intent = new Intent(getApplicationContext(), MainActivity.class);
                startActivity(intent);
            }
        });

        /* Add IP Button */
        btn_add = (Button) findViewById(R.id.btn_add);
        btn_add.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {
                String new_server_ip = null, new_server_name = null;

                ArrayList<String> server_name_list = new ArrayList<String>();
                ArrayList<String> server_ip_list = new ArrayList<String>();

                new_server_ip = server_ip.getText().toString();
                server_ip_list.add(new_server_ip);

                new_server_name = server_name.getText().toString();
                server_name_list.add(new_server_name);
            }
        });

        return rootView;
    }
}

我的错误日志只说，我必须在我的 Manifest.xml 中添加 fragment 作为 Activity 。但我知道，我不必在此处添加它。

错误日志

11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime: FATAL EXCEPTION: main
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime: Process: de.kwietzorek.fulcrumwebview, PID: 18345
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime: android.content.ActivityNotFoundException: Unable to find explicit activity class {de.kwietzorek.fulcrumwebview/de.kwietzorek.fulcrumwebview.MainActivity$AddServerFragment}; have you declared this activity in your AndroidManifest.xml?
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.app.Instrumentation.checkStartActivityResult(Instrumentation.java:1794)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.app.Instrumentation.execStartActivity(Instrumentation.java:1512)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.app.Activity.startActivityForResult(Activity.java:3917)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.app.Activity.startActivityForResult(Activity.java:3877)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:784)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.app.Activity.startActivity(Activity.java:4200)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.app.Activity.startActivity(Activity.java:4168)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at de.kwietzorek.fulcrumwebview.MainActivity.onOptionsItemSelected(MainActivity.java:90)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.app.Activity.onMenuItemSelected(Activity.java:2908)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:361)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.support.v7.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:147)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.support.v7.internal.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:100)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.support.v7.app.AppCompatDelegateImplV7.onMenuItemSelected(AppCompatDelegateImplV7.java:621)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.support.v7.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:811)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.support.v7.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:153)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.support.v7.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:958)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.support.v7.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:948)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.support.v7.internal.view.menu.MenuPopupHelper.onItemClick(MenuPopupHelper.java:191)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.widget.AdapterView.performItemClick(AdapterView.java:310)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.widget.AbsListView.performItemClick(AbsListView.java:1145)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.widget.AbsListView$PerformClick.run(AbsListView.java:3042)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.widget.AbsListView$3.run(AbsListView.java:3879)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.os.Handler.handleCallback(Handler.java:739)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:95)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:148)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5417)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
11-14 15:22:05.935 18345-18345/de.kwietzorek.fulcrumwebview E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

编辑

我的 list .xml

<?xml version="1.0" encoding="utf-8"?>

<uses-permission android:name="android.permission.INTERNET" />

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/Theme.AppCompat" >
    <activity android:name=".MainActivity" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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

Answer 1

Wrong with the above code:

错误 Intent intent = new Intent(getApplicationContext(), AddServerFragment.class); 启动 Activity ( Intent )；

    Use the correct method for using fragment, you have used method for starting activity.

AddServerFragment 是 fragment 而不是 Activity 。

要在 Activity 中添加 fragment ，您必须使用以下方法:

在你的 Activity 中，

activity_main.xml 中的 XML 代码部分:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/fragment_container"
     android:layout_width="match_parent"
     android:layout_height="match_parent" />

MainActivity.class 中的 Java 代码部分:

    if (findViewById(R.id.fragment_container) != null) {

        if (savedInstanceState != null) {
            return;
        }

        // Create an instance of AddServerFragment
        AddServerFragment firstFragment = new AddServerFragment();
        // if there are any extras
        firstFragment.setArguments(getIntent().getExtras());

        // Add the fragment to the 'fragment_container' FrameLayout
        getSupportFragmentManager().beginTransaction()
                .add(R.id.fragment_container, firstFragment).commit();
    }