Question

在类OilPlots中我有以下方法，它应该加载Activity BoPlots：

OnClickListener OilList = new OnClickListener() {

    public void onClick(View view) {

        Intent intent = new Intent(OilPlots.this, BoPlots.class);
        startActivity(intent);
    }
    };

以下是BoPlots的onCreate（）方法：

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

        setup();        
        color(button4, R.id.buttonLayout ,R.id.button4);

        Button btn = (Button)findViewById(R.id.bo);
        btn.setOnClickListener(BoList);

    }

我第一次加载Activity BoPlots时它加载正常，但如果我尝试从OilPlots类访问它，它会崩溃应用程序。 logcat如下：

08-18 22:06:15.649: E/AndroidRuntime(32339): FATAL EXCEPTION: main
08-18 22:06:15.649: E/AndroidRuntime(32339): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.resengin/com.example.resengin.BoPlots}: java.lang.NullPointerException
08-18 22:06:15.649: E/AndroidRuntime(32339):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at android.app.ActivityThread.access$600(ActivityThread.java:130)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at android.os.Handler.dispatchMessage(Handler.java:99)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at android.os.Looper.loop(Looper.java:137)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at android.app.ActivityThread.main(ActivityThread.java:4745)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at java.lang.reflect.Method.invokeNative(Native Method)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at java.lang.reflect.Method.invoke(Method.java:511)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at dalvik.system.NativeStart.main(Native Method)
08-18 22:06:15.649: E/AndroidRuntime(32339): Caused by: java.lang.NullPointerException
08-18 22:06:15.649: E/AndroidRuntime(32339):    at java.lang.StringToReal.parseFloat(StringToReal.java:285)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at java.lang.Float.parseFloat(Float.java:300)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at java.lang.Float.valueOf(Float.java:337)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at com.example.resengin.BoResults.onCreate(BoResults.java:74)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at com.example.resengin.BoPlots.onCreate(BoPlots.java:20)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at android.app.Activity.performCreate(Activity.java:5008)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
08-18 22:06:15.649: E/AndroidRuntime(32339):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
08-18 22:06:15.649: E/AndroidRuntime(32339):    ... 11 more

据我所知，崩溃的原因是：

08-18 22:06:15.649: E/AndroidRuntime(32339): Caused by: java.lang.NullPointerException
08-18 22:06:15.649: E/AndroidRuntime(32339):    at java.lang.StringToReal.parseFloat(StringToReal.java:285)

导致崩溃，因为该变量尚未实例化。这似乎引用的代码行在Activity BoResults中。此活动的onCreate方法如下：

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

        setup();        
        color(button3, R.id.buttonLayout ,R.id.button3);

        txt1=(TextView)findViewById(R.id.results).findViewById(R.id.editText1);
        txt2=(TextView)findViewById(R.id.results).findViewById(R.id.editText2);
        txt3=(TextView)findViewById(R.id.results).findViewById(R.id.editText3);

        Intent intent = getIntent();        

        Float Pressure = Float.valueOf(intent.getStringExtra("V1"));
        Float Temp = Float.valueOf(intent.getStringExtra("V2"));
        Float STOG = Float.valueOf(intent.getStringExtra("V3"));
        Float SG = Float.valueOf(intent.getStringExtra("V4"));
        Float SGOR = Float.valueOf(intent.getStringExtra("V5"));


        txt1.setText(String.valueOf(Pressure));
        txt2.setText(String.valueOf(Temp));
        txt3.setText(String.valueOf(STOG));   

        spreadsheet();

    }

但我不明白为什么要调用它，因为代码中没有任何内容可以引用BoResults Activity中的任何内容，或者调用任何方法。 BoPlots确实扩展了BoResults

Answer 1

所以BoPlots扩展了BoResults？在您的BoPlots onCreate方法中，您将调用super.onCreate，它将调用BoResults版本。因此，如果您没有为BoResults需要的BoPlots意图添加相同的额外内容，它将崩溃。听起来你不应该扩展BoResults。

Answer 2

如果密钥的映射值不存在，则

getStringExtra返回null。如果您尝试将null转换为float，则应用程序将崩溃

Android Activity导致应用程序崩溃，但就我所见，它在任何时候都没有被调用

2 个答案: