java - 不幸的是<项目名称>已停止消息

Question

我是 Android 新手，正在使用 Android studio。我创建了一个带有两个按钮的基本程序。但是一旦我启动模拟器，应用程序就不会启动。我收到一条消息，提示“不幸的是 -项目名称-已停止'。但是代码编译没有任何错误。这里我附上代码。

AndroidMAnifest.xml

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

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.projectdrogo.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>
    </application>

</manifest>

这是我的 MainActivity.java 代码

package com.example.projectdrogo;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.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;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends ActionBarActivity {
    int counter;
    Button add,subtract;
    TextView textview;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        counter =0;
        add = (Button)findViewById(R.id.bAdd);
        subtract=(Button)findViewById(R.id.bSubtract);
        textview=(TextView)findViewById(R.id.textView);
        add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                counter++;
                textview.setText("Your Total is "+counter);
            }
        });
        subtract.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                counter--;
                textview.setText("Your Total is "+counter);
            }
        });

        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;
        }
    }

}

这是我的 main.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    tools:context="com.example.projectdrogo.MainActivity" >

    <item android:id="@+id/action_settings"
        android:title="@string/action_settings"
        android:orderInCategory="100"
        app:showAsAction="never" />
</menu>

activity_main.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.projectdrogo.MainActivity"
    tools:ignore="MergeRootFrame" />

fragment_main.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:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context="com.example.projectdrogo.MainActivity$PlaceholderFragment">

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:weightSum="1">
        <TextView
            android:text="@string/name"
            android:textSize="50dp"
            android:textColor="#FF0000"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:id="@+id/textView" />


        <Button
            style="?android:attr/buttonStyleSmall"
            android:layout_width="300dp"
            android:layout_height="wrap_content"
            android:text="Subtract One"
            android:id="@+id/bSubtract"
            android:textSize="30dp"
            android:layout_gravity="center"
            />

        <Button
            style="?android:attr/buttonStyleSmall"
            android:layout_width="300dp"
            android:layout_height="wrap_content"
            android:text="Add One"
            android:id="@+id/bAdd"
            android:layout_gravity="center"
            android:textSize="30dp" />

    </LinearLayout>

</RelativeLayout>

请帮助我，我陷入困境。谢谢

Answer 1

activity_main.xml 没有按钮或 TextView 。看起来像是在 fragment 布局中

我猜你有一个 fragment

PlaceholderFragment newFragment = new  PlaceholderFragment();
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.add(R.id.container, newFragment);
transaction.addToBackStack(null);
transaction.commit();

然后在Fragment的onCreateView中

 View rootView = inflater.inflate(R.layout.fragment_main, container, false);
 add = (Button)rootView.findViewById(R.id.bAdd);
 subtract=(Button)rootView.findViewById(R.id.bSubtract);
 textview=(TextView)rootView.findViewById(R.id.name);
 ...// rest of the code

你有一个FrameLayout，它是一个容器。您需要将 fragment 添加到容器中。 Activity 中的 View 也属于 fragment 布局。因此，您需要按照建议在 onCreateView 中初始化相同的内容。

编辑:

public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    PlaceholderFragment newFragment = new  PlaceholderFragment();
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    transaction.add(R.id.container, newFragment);
    transaction.addToBackStack(null);
    transaction.commit();
}

然后

公共(public)静态类 PlaceholderFragment 扩展 Fragment {

    int counter;
    Button add,subtract;
    TextView textview;
    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);   
        add = (Button)rootView.findViewById(R.id.bAdd);
        subtract=(Button)rootView.findViewById(R.id.bSubtract);
        textview=(TextView)rootView.findViewById(R.id.name);
        ... // rest of the code

        return rootView;
    }
}