Question

我是Android应用程序开发的初学者，正在制作一个简单的应用程序来添加和减去。我在模拟器或手机（Galaxy Y duos）上传时会反复出现此错误。

logcat的：

06-05 16:22:17.402: E/Trace(1759): error opening trace file: No such file or directory (2)
06-05 16:22:17.513: E/AndroidRuntime(1759): FATAL EXCEPTION: main
06-05 16:22:17.513: E/AndroidRuntime(1759): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.levelone/com.example.levelone.MainActivity}: java.lang.NullPointerException
06-05 16:22:17.513: E/AndroidRuntime(1759):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at android.os.Handler.dispatchMessage(Handler.java:99)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at android.os.Looper.loop(Looper.java:137)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at android.app.ActivityThread.main(ActivityThread.java:5039)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at java.lang.reflect.Method.invokeNative(Native Method)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at java.lang.reflect.Method.invoke(Method.java:511)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at dalvik.system.NativeStart.main(Native Method)
06-05 16:22:17.513: E/AndroidRuntime(1759): Caused by: java.lang.NullPointerException
06-05 16:22:17.513: E/AndroidRuntime(1759):     at com.example.levelone.MainActivity.onCreate(MainActivity.java:22)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at android.app.Activity.performCreate(Activity.java:5104)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
06-05 16:22:17.513: E/AndroidRuntime(1759):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
06-05 16:22:17.513: E/AndroidRuntime(1759):     ... 11 more

Mainactivity.java：

package com.example.levelone;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {

    int counter;
    Button add, sub;
    TextView display;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        counter=0;
        add = (Button) findViewById(R.id.badd);
        sub = (Button) findViewById(R.id.bsub);
        display = (TextView) findViewById(R.id.tvdisplay);
        add.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                counter++;
                display.setText("Your total is " + counter);
            }
        });
        sub.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                counter--;
                display.setText("Your total is " + counter);
            }
        });


        }

}

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: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.levelone.MainActivity$PlaceholderFragment" >

    <TextView
        android:id="@+id/tvdisplay"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="32dp"
        android:text="Your score is 0" />

    <Button
        android:id="@+id/badd"
        android:layout_width="250dp"
        android:layout_height="wrap_content"
        android:layout_below="@+id/tvdisplay"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="39dp"
        android:text="Add one" />

    <Button
        android:id="@+id/bsub"
        android:layout_width="250dp"
        android:layout_height="wrap_content"
        android:layout_below="@+id/badd"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="32dp"
        android:text="Subtract one" />

</RelativeLayout>

的AndroidManifest.xml

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

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

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

请帮忙。我无法继续进一步

Answer 1

替换MainActivity java文件中的以下内容

setContentView(R.layout.activity_main);

与

setContentView(R.layout.fragment_main);

不幸的是<app>停止了工作</app>

1 个答案: