Android HelloWorld 应用程序在执行第二个 Activity 时崩溃

Question

我正在尝试完成 Android HelloWorld App使用 Eclipse 和 ADT。但是，当我执行第二个 Activity 并按下“发送”按钮时，应用程序总是崩溃。以下是相关文件(导入被截断):

fragment _main.xml

<LinearLayout 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:orientation="horizontal"
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.example.myfirstapp.MainActivity$PlaceholderFragment" >

<EditText android:id="@+id/edit_message"
    android:layout_weight="1"        
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:hint="@string/edit_message" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/button_send"
    android:onClick="sendMessage" />  

fragment_display_message.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.example.myfirstapp.DisplayMessageActivity$PlaceholderFragment" >

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/hello_world" />

activity_display_message.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.myfirstapp.DisplayMessageActivity"
tools:ignore="MergeRootFrame" />

主 Activity .java

public class MainActivity extends ActionBarActivity {

public final static String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";

public void sendMessage(View view) {
    Intent intent = new Intent(this, DisplayMessageActivity.class);
    EditText editText = (EditText) findViewById(R.id.edit_message);
    String message = editText.getText().toString();
    intent.putExtra(EXTRA_MESSAGE, message);
    startActivity(intent);
}

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

    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment()).commit();
    }
}

@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);
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {

    public PlaceholderFragment() {
    }

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

}

DisplayMessageActivity.java

public class DisplayMessageActivity extends ActionBarActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {    
    super.onCreate(savedInstanceState);     
    Intent intent = getIntent();
    String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
    TextView textView = new TextView(this);
    textView.setTextSize(40);
    textView.setText(message);
    setContentView(textView);

    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment()).commit();
    }

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {

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

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {

    public PlaceholderFragment() {
    }

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

}

AndroidManifest.xml

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

<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="19" />

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

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name="com.example.myfirstapp.DisplayMessageActivity"
        android:label="@string/title_activity_display_message"
        android:parentActivityName="com.example.myfirstapp.MainActivity" >
        <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value="com.example.myfirstapp.MainActivity" />
    </activity>
</application>

最后，LogCat 文件:

03-20 22:25:46.427: E/AndroidRuntime(32293): FATAL EXCEPTION: main
03-20 22:25:46.427: E/AndroidRuntime(32293): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myfirstapp/com.example.myfirstapp.DisplayMessageActivity}: java.lang.IllegalArgumentException: No view found for id 0x7f05003c (com.example.myfirstapp:id/container) for fragment PlaceholderFragment{4137cd30 #0 id=0x7f05003c}
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1968)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1993)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.app.ActivityThread.access$600(ActivityThread.java:127)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1159)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.os.Handler.dispatchMessage(Handler.java:99)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.os.Looper.loop(Looper.java:137)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.app.ActivityThread.main(ActivityThread.java:4507)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at java.lang.reflect.Method.invokeNative(Native Method)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at java.lang.reflect.Method.invoke(Method.java:511)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:978)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:745)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at dalvik.system.NativeStart.main(Native Method)
03-20 22:25:46.427: E/AndroidRuntime(32293): Caused by: java.lang.IllegalArgumentException: No view found for id 0x7f05003c (com.example.myfirstapp:id/container) for fragment PlaceholderFragment{4137cd30 #0 id=0x7f05003c}
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:919)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:570)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1136)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.app.Activity.performStart(Activity.java:4479)
03-20 22:25:46.427: E/AndroidRuntime(32293):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1941)
03-20 22:25:46.427: E/AndroidRuntime(32293):    ... 11 more

我知道问题在于 DisplayMessageActivity.java 中 onCreate 的条件，但我不知道如何解决它。如果您能帮助我理解为什么这个简单的应用程序(本质上是从 Android 站点复制粘贴的)无法运行，我将不胜感激。

Answer 1

我遇到了类似的问题。当我重新检查你也在学习的教程，即 developer.android 时，我发现在 DisplayMessageActivity 类的 onCreate 方法中，以下行代码导致中断，(我已经评论了)

if (savedInstanceState == null) {
       getSupportFragmentManager().beginTransaction()
               .add(R.id.container, PlaceholderFragment.newInstance(message)).commit();
   }

请删除这些行。如果您仔细观察那里的教程，他们最后展示了 onCreate 的代码以进行交叉检查，那里缺少这些行。 :)