java.lang.RuntimeException : Unable to instantiate activity ComponentInfo: java. lang.NullPointerException 异常

Question

当我想继续其他 Activity 时，我遇到了这个异常:

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{ua.kbv.adviser/ua.kbv.adviser.AdviceWithText}: java.lang.NullPointerException
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
    at android.app.ActivityThread.access$600(ActivityThread.java:141)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:5041)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:511)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
    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 ua.kbv.adviser.AdviceWithText.<init>(AdviceWithText.java:18)
    at java.lang.Class.newInstanceImpl(Native Method)
    at java.lang.Class.newInstance(Class.java:1319)
    at android.app.Instrumentation.newActivity(Instrumentation.java:1054)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
    at android.app.ActivityThread.access$600(ActivityThread.java:141)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:5041)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:511)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
    at dalvik.system.NativeStart.main(Native Method)

list :

<application android:allowBackup="true"
    android:label="@string/app_name"
    android:icon="@mipmap/ic_launcher"
    android:theme="@style/AppTheme">

    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN"/>
            <category android:name="android.intent.category.LAUNCHER"/>
        </intent-filter>
    </activity>

    <activity android:name=".AdviceWithText"/>
    <activity android:name=".AdviceWithoutText"/>
    <supports-screens
        android:smallScreens="true"
        android:normalScreens="true"
        android:largeScreens="true"
        android:anyDensity="true"
        />
</application>

主要 Activity :

public class MainActivity extends Activity{

    private static long back_pressed;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_layout);
    }

    public void clickOnGetAdvice(View view){


        AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);

        builder.setTitle(R.string.builderTitle)
                .setMessage(R.string.builderMessage)
                .setCancelable(true)
                .setIcon(R.mipmap.ic_action)
                .setNeutralButton(R.string.neutralButton, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        Intent intent = new Intent(MainActivity.this, AdviceWithText.class);
                        startActivity(intent);
                        dialog.dismiss();
                    }
                })
                .setPositiveButton(R.string.positivebutton, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        Intent intent = new Intent(MainActivity.this, AdviceWithoutText.class);
                        startActivity(intent);
                        dialog.dismiss();
                    }
                });

        AlertDialog alert = builder.create();
        alert.show();
    }

    @Override
    public void onBackPressed() {
        if (back_pressed + 2000 > System.currentTimeMillis()) {
            super.onBackPressed();
        } else {
            Toast.makeText(getBaseContext(), R.string.exitToast, Toast.LENGTH_SHORT).show();
        }

        back_pressed = System.currentTimeMillis();

    }

    public void clickOnAbout(View view){
        AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
        builder.setTitle(R.string.builderAboutTitle)
                .setMessage(R.string.builderMessageAbout)
                .setCancelable(true)
                .setIcon(R.mipmap.ic_action_info)
                .setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.dismiss();
                    }
                });

        AlertDialog alertDialog = builder.create();
        alertDialog.show();

    }

        @Override
        protected void onDestroy () {
            super.onDestroy();
            System.exit(0); 
        }
}

接收 Activity :

public class AdviceWithText extends Activity{

     TextView answer;
     private EditText question;
     String [] advices = getResources().getStringArray(R.array.advices);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.with_layout);
    }

    public void getAdvice(View view){
        answer = (TextView) findViewById(R.id.answerText);
        question = (EditText) findViewById(R.id.questionWith);
        String text = question.getText().toString();
        int rand = (int) Math.floor(Math.random()* advices.length);
        if(text.equals("")){
            Toast.makeText(getApplicationContext(),R.string.toastWith, Toast.LENGTH_LONG).show();
        } else if(text.matches("[0-9]+")) {
            Toast.makeText(getApplicationContext(),R.string.toastWithSecond, Toast.LENGTH_LONG).show();
        } else {
            answer.setText(advices[rand]);
        }
    }

    @Override
    public void onBackPressed() {
        finish();
    }

    public void reset(View view){
        question = (EditText) findViewById(R.id.questionWith);
        question.setText("");
        answer.setText("");

    }

}

Answer 1

您正在从初始化器调用 getResources()，这将不起作用。通常，在 super.onCreate() 返回之前不要调用 Activity 上的方法，除非有指示这样做。

在这种情况下，替换:

String [] advices = getResources().getStringArray(R.array.advices);

与:

String [] advices;

并添加:

advices = getResources().getStringArray(R.array.advices);

在 onCreate() 方法中的 super.onCreate() 之后。