Android第一个应用程序错误（启动另一个活动）

我在加载另一个活动时遇到问题。当我单击“发送”按钮时，应用程序停止。有人能确定我的错误吗

这是我的MainActivity.java

    package com.example.myfirstapp;

    import android.content.Intent;
    import android.os.Bundle;
    import android.support.v4.app.Fragment;
    import android.support.v7.app.ActionBarActivity;
    import android.view.LayoutInflater;
    import android.view.Menu;
    import android.view.MenuItem;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.EditText;

    public class MainActivity extends ActionBarActivity {
        public final static String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";

        @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);
        }
        /** Called when the user clicks the Send button */
        public void sendMessage(View view) {
            Intent intent = new Intent(MainActivity.this, DisplayMessageActivity.class);
            EditText editText = (EditText) findViewById(R.id.edit_message);
            String message = editText.getText().toString();
            intent.putExtra(EXTRA_MESSAGE, message);
            startActivity(intent);
        }

/**
 * 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;
            }
        }

    }

以下是我的DisplayMeassageActivity.java：

    public class DisplayMessageActivity extends ActionBarActivity {


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);


    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment()).commit();
    }
    Intent intent = getIntent();
    String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
    TextView textView = new TextView(this);
    textView.setTextSize(40);
    textView.setText(message);
    setContentView(textView);
}

@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;
    }
}

}

这是我的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" 
            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" />    
    </LinearLayout>

和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>

    </manifest>

问题在于您的
DisplayMessageActivity
onCreate

您正试图在设置
contentView
之前添加
片段

另外，您的
setContentView（textView）
只设置了
textView

因此，在找到
视图之前，您需要删除添加片段的代码或创建布局并设置
ContentView
，当然，您需要日志。如果您不知道日志在哪里，请在eclipse中单击窗口->显示视图->其他->android->logcat。运行您的应用程序，然后向我们显示日志错误（如果您知道如何查找错误，请显示与错误相关的行）