Question

我是Android的新手，我正在编写一个简单的程序来执行基本计算，例如加，减，除和乘以及使用意图但是当我尝试运行我的程序的一半来检查时，它给出了一个错误：< / p>

这是我的主文件......

package com.example.ruupali;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class Calculate extends Activity implements OnClickListener{
    Button add,sub,mul,divide;
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    add=(Button) findViewById(R.id.buttADD);
    sub=(Button) findViewById(R.id.buttSUB);
    mul=(Button) findViewById(R.id.buttMUL);
    divide=(Button) findViewById(R.id.buttDIVIDE);
    add.setOnClickListener(this);
    sub.setOnClickListener(this);
    mul.setOnClickListener(this);
    divide.setOnClickListener(this);
    }
    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        switch(v.getId()){
        case R.id.buttADD:
            Intent intent = new Intent(this, Add.class);
            this.startActivity(intent);
            break;

        case R.id.buttSUB:
            Intent intent1 = new Intent(this, Add.class);
            this.startActivity(intent1);
            break;
        case R.id.buttMUL:
            Intent intent2= new Intent(this, Add.class);
            this.startActivity(intent2);
            break;
        case R.id.buttDIVIDE:
            Intent intent3 = new Intent(this, Add.class);
            this.startActivity(intent3);
            break;
        }
    }
}

我的xml文件......

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <Button
        android:id="@+id/buttADD"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="ADD" />

    <Button
        android:id="@+id/buttSUB"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="SUBTRACT" />

    <Button
        android:id="@+id/buttMUL"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="MULTIPLY"/>

    <Button
        android:id="@+id/buttDIVIDE"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="DIVIDE" />
</LinearLayout>

清单文件......

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

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="21" />

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

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
        <activity
            android:name=".Menu"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="com.example.ruupali.MENU" />

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
         <activity
            android:name=".TextPlay"
            android:label="@string/app_name" >
        </activity>
          <activity
            android:name=".Email"
            android:label="@string/app_name" >
        </activity>
        <activity
            android:name=".Calculate"
            android:label="@string/app_name" >
        </activity>
    </application>

</manifest>

... logcat中

07-29 15:35:23.401: D/dalvikvm(1270): GC_FOR_ALLOC freed 35K, 4% free 3548K/3660K, paused 12ms, total 12ms
07-29 15:35:23.409: I/dalvikvm-heap(1270): Grow heap (frag case) to 4.306MB for 805388-byte allocation
07-29 15:35:23.417: D/dalvikvm(1270): GC_FOR_ALLOC freed <1K, 3% free 4334K/4448K, paused 9ms, total 9ms
07-29 15:35:24.229: E/MediaPlayer(1270): Should have subtitle controller already set
07-29 15:35:24.253: D/libEGL(1270): loaded /system/lib/egl/libEGL_genymotion.so
07-29 15:35:24.253: D/(1270): HostConnection::get() New Host Connection established 0xb96e7ae8, tid 1270
07-29 15:35:24.277: D/libEGL(1270): loaded /system/lib/egl/libGLESv1_CM_genymotion.so
07-29 15:35:24.281: D/libEGL(1270): loaded /system/lib/egl/libGLESv2_genymotion.so
07-29 15:35:24.361: W/EGL_genymotion(1270): eglSurfaceAttrib not implemented
07-29 15:35:24.361: E/OpenGLRenderer(1270): Getting MAX_TEXTURE_SIZE from GradienCache
07-29 15:35:24.365: E/OpenGLRenderer(1270): MAX_TEXTURE_SIZE: 16384
07-29 15:35:24.381: E/OpenGLRenderer(1270): Getting MAX_TEXTURE_SIZE from Caches::initConstraints()
07-29 15:35:24.381: E/OpenGLRenderer(1270): MAX_TEXTURE_SIZE: 16384
07-29 15:35:24.381: D/OpenGLRenderer(1270): Enabling debug mode 0
07-29 15:35:29.241: D/dalvikvm(1270): GC_FOR_ALLOC freed 7K, 2% free 4585K/4672K, paused 3ms, total 3ms
07-29 15:35:29.245: I/dalvikvm-heap(1270): Grow heap (frag case) to 6.970MB for 2536932-byte allocation
07-29 15:35:29.253: D/dalvikvm(1270): GC_FOR_ALLOC freed <1K, 2% free 7062K/7152K, paused 6ms, total 6ms
07-29 15:35:29.389: W/EGL_genymotion(1270): eglSurfaceAttrib not implemented
07-29 15:35:34.129: D/AndroidRuntime(1270): Shutting down VM
07-29 15:35:34.129: W/dalvikvm(1270): threadid=1: thread exiting with uncaught exception (group=0xa4d3db20)
07-29 15:35:34.137: E/AndroidRuntime(1270): FATAL EXCEPTION: main
07-29 15:35:34.137: E/AndroidRuntime(1270): Process: com.example.ruupali, PID: 1270
07-29 15:35:34.137: E/AndroidRuntime(1270): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ruupali/com.example.ruupali.Calculate}: java.lang.NullPointerException
07-29 15:35:34.137: E/AndroidRuntime(1270):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at android.os.Handler.dispatchMessage(Handler.java:102)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at android.os.Looper.loop(Looper.java:136)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at android.app.ActivityThread.main(ActivityThread.java:5001)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at java.lang.reflect.Method.invokeNative(Native Method)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at java.lang.reflect.Method.invoke(Method.java:515)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at dalvik.system.NativeStart.main(Native Method)
07-29 15:35:34.137: E/AndroidRuntime(1270): Caused by: java.lang.NullPointerException
07-29 15:35:34.137: E/AndroidRuntime(1270):     at com.example.ruupali.Calculate.onCreate(Calculate.java:19)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at android.app.Activity.performCreate(Activity.java:5231)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
07-29 15:35:34.137: E/AndroidRuntime(1270):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
07-29 15:35:34.137: E/AndroidRuntime(1270):     ... 11 more
07-29 15:35:36.241: I/Process(1270): Sending signal. PID: 1270 SIG: 9

现在再次检查所有

nw logcat ...

07-29 16:27:44.390: E/MediaPlayer(1778): Should have subtitle controller already set
07-29 16:27:44.506: W/EGL_genymotion(1778): eglSurfaceAttrib not implemented
07-29 16:27:49.466: W/EGL_genymotion(1778): eglSurfaceAttrib not implemented
07-29 16:27:56.582: D/dalvikvm(1778): GC_FOR_ALLOC freed 22K, 3% free 7141K/7352K, paused 3ms, total 3ms
07-29 16:27:56.714: W/EGL_genymotion(1778): eglSurfaceAttrib not implemented
07-29 16:27:58.606: D/AndroidRuntime(1778): Shutting down VM
07-29 16:27:58.606: W/dalvikvm(1778): threadid=1: thread exiting with uncaught exception (group=0xa4d6cb20)
07-29 16:27:58.606: E/AndroidRuntime(1778): FATAL EXCEPTION: main
07-29 16:27:58.606: E/AndroidRuntime(1778): Process: com.example.ruupali, PID: 1778
07-29 16:27:58.606: E/AndroidRuntime(1778): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.ruupali/com.example.ruupali.Add}: java.lang.ClassCastException: com.example.ruupali.Add cannot be cast to android.app.Activity
07-29 16:27:58.606: E/AndroidRuntime(1778):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
07-29 16:27:58.606: E/AndroidRuntime(1778):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
07-29 16:27:58.606: E/AndroidRuntime(1778):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
07-29 16:27:58.606: E/AndroidRuntime(1778):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
07-29 16:27:58.606: E/AndroidRuntime(1778):     at android.os.Handler.dispatchMessage(Handler.java:102)
07-29 16:27:58.606: E/AndroidRuntime(1778):     at android.os.Looper.loop(Looper.java:136)
07-29 16:27:58.606: E/AndroidRuntime(1778):     at android.app.ActivityThread.main(ActivityThread.java:5001)
07-29 16:27:58.606: E/AndroidRuntime(1778):     at java.lang.reflect.Method.invokeNative(Native Method)
07-29 16:27:58.606: E/AndroidRuntime(1778):     at java.lang.reflect.Method.invoke(Method.java:515)
07-29 16:27:58.606: E/AndroidRuntime(1778):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
07-29 16:27:58.606: E/AndroidRuntime(1778):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
07-29 16:27:58.606: E/AndroidRuntime(1778):     at dalvik.system.NativeStart.main(Native Method)
07-29 16:27:58.606: E/AndroidRuntime(1778): Caused by: java.lang.ClassCastException: com.example.ruupali.Add cannot be cast to android.app.Activity
07-29 16:27:58.606: E/AndroidRuntime(1778):     at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
07-29 16:27:58.606: E/AndroidRuntime(1778):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2101)
07-29 16:27:58.606: E/AndroidRuntime(1778):     ... 11 more
07-29 16:28:00.686: I/Process(1778): Sending signal. PID: 1778 SIG: 9
07-29 16:28:00.906: D/dalvikvm(1845): GC_FOR_ALLOC freed 43K, 6% free 3771K/4008K, paused 14ms, total 15ms
07-29 16:28:00.910: I/dalvikvm-heap(1845): Grow heap (frag case) to 6.284MB for 2536932-byte allocation
07-29 16:28:00.950: D/dalvikvm(1845): GC_FOR_ALLOC freed <1K, 4% free 6248K/6488K, paused 40ms, total 40ms
07-29 16:28:01.142: D/libEGL(1845): loaded /system/lib/egl/libEGL_genymotion.so
07-29 16:28:01.142: D/(1845): HostConnection::get() New Host Connection established 0xb901d8e0, tid 1845
07-29 16:28:01.174: D/libEGL(1845): loaded /system/lib/egl/libGLESv1_CM_genymotion.so
07-29 16:28:01.174: D/libEGL(1845): loaded /system/lib/egl/libGLESv2_genymotion.so
07-29 16:28:01.274: W/EGL_genymotion(1845): eglSurfaceAttrib not implemented
07-29 16:28:01.278: E/OpenGLRenderer(1845): Getting MAX_TEXTURE_SIZE from GradienCache
07-29 16:28:01.278: E/OpenGLRenderer(1845): MAX_TEXTURE_SIZE: 16384
07-29 16:28:01.302: E/OpenGLRenderer(1845): Getting MAX_TEXTURE_SIZE from Caches::initConstraints()
07-29 16:28:01.306: E/OpenGLRenderer(1845): MAX_TEXTURE_SIZE: 16384
07-29 16:28:01.306: D/OpenGLRenderer(1845): Enabling debug mode 0

Answer 1

替换

setContentView(R.layout.activity_main);

使用

setContentView(R.layout.calculate);

当你有按钮时 calculate.xml而不是activity_main.xml。这就是你获得NPE的原因

<强>更新

替换

 Intent intent = new Intent(this, Add.class);
        this.startActivity(intent);

使用

            Intent intent = new Intent(Calculator.this, Add.class);
        startActivity(intent);

Android简单计算器应用程序崩溃

1 个答案: