Question

我成功编译了一个Android应用程序并创建了它的apk。我还用我的密钥库签署了.apk文件。但是在USB调试模式下运行时，由于某种原因，它会给我一个NullPointerException。

以下是例外：

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06-16 15:23:11.639  30531-30531/com.adi.play E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.adi.play/com.adi.play.PlayActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2277)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2403)
            at android.app.ActivityThread.access$600(ActivityThread.java:165)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1373)
            at android.os.Handler.dispatchMessage(Handler.java:107)
            at android.os.Looper.loop(Looper.java:194)
            at android.app.ActivityThread.main(ActivityThread.java:5391)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at android.content.ContextWrapper.getResources(ContextWrapper.java:89)
            at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:78)
            at com.adi.play.PlayActivity.<init>(PlayActivity.java:12)
            at java.lang.Class.newInstanceImpl(Native Method)
            at java.lang.Class.newInstance(Class.java:1319)
            at android.app.Instrumentation.newActivity(Instrumentation.java:1123)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2268)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2403)
            at android.app.ActivityThread.access$600(ActivityThread.java:165)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1373)
            at android.os.Handler.dispatchMessage(Handler.java:107)
            at android.os.Looper.loop(Looper.java:194)
            at android.app.ActivityThread.main(ActivityThread.java:5391)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)

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我的AndroidManifest.xml文件：

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<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.adi.play"
      android:versionCode="1"
      android:versionName="1.0">
    <application android:label="@string/app_name" 
    	android:icon="@drawable/me">
        <activity android:name="PlayActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

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我的com.adi.play.PlayActivity .java文件：

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package com.adi.play;

import android.os.Bundle;
import android.app.Activity;
import android.widget.Button;
import android.widget.TextView;
import android.view.View;
import android.view.View.OnClickListener;

public class PlayActivity extends Activity {

	public final String RESULT = getResources().getString(R.string.result);
	
	private int total = 0;
	private TextView displayResult;
	private Button incrementButton;
	private Button decrementButton;

	@Override
	public void onCreate(Bundle bundle) {
	
		super.onCreate(bundle);
		setContentView(R.layout.activity_play);
		
		displayResult = (TextView)findViewById(R.id.display_result);
		incrementButton = (Button)findViewById(R.id.increment_button);
		decrementButton = (Button)findViewById(R.id.decrement_button);
		
		displayResult.setText(RESULT+total);
		incrementButton.setOnClickListener(new View.OnClickListener() {
		
			@Override
			public void onClick(View view) {
			
				total++;
				displayResult.setText(RESULT+total);
			}
		});
		
		decrementButton.setOnClickListener(new View.OnClickListener() {
		
			@Override
			public void onClick(View view) {
			
				total--;
				displayResult.setText(RESULT+total);
			}
		});
	}
}

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请帮忙。这件事让我烦恼。

Answer 1

这一行引起了它

public final String RESULT = getResources().getString(R.string.result);

getResources()方法在调用期间需要context，运行时没有可用的上下文。

<强>解决方案：

在onCreate上初始化RESULT：

public class PlayActivity extends Activity {

private String result; //this line

private int total = 0;
private TextView displayResult;
private Button incrementButton;
private Button decrementButton;

@Override
public void onCreate(Bundle bundle) {

    super.onCreate(bundle);
    setContentView(R.layout.activity_play);

    result = getResources().getString(R.string.result); //this line

Answer 2

这是你的问题，我不知道你的IDE如何不抱怨：

public final String RESULT = getResources().getString(R.string.result);

尝试在onCreate（）;

中为RESULT分配值

Here您可以在Android中找到有关资源使用的官方文档以及如何访问资源。

Answer 3

i需要在getResources()执行后创建的Context。

试试这段代码。

onCreate()

APK已创建但未在设备

3 个答案: