java - 将 double 从一项 Activity 转移到另一项 Activity

Question

我正在尝试将通过 EditText 获得的变量传输到下一个 Activity 中。起初，我只用一个变量尝试过，效果很好。但是一旦我添加了第二个 Activity ，应用程序就开始崩溃一旦我尝试过。当我尝试按下按钮进入第二个 Activity 时，应用程序崩溃了。也许你能找到错误？

以下是我的代码。

第一个 Activity :

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

    Button weiter = (Button) findViewById(R.id.weiter1);
    weiter.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            EditText inputHeight = (EditText) findViewById(R.id.inputheight);
            EditText inputlenght = (EditText) findViewById(R.id.inputlenght);

            Double height = Double.parseDouble(inputHeight.getText().toString());
            String Höhe = new Double(height).toString();

            Double lenght = Double.parseDouble(inputlenght.getText().toString());
            String Länge = new Double(lenght).toString();

            Intent i = new Intent(getApplicationContext(), Main2Activity.class);
            i.putExtra("HöheName", Höhe);
            i.putExtra( "LängeName", Länge);
            startActivity(i);
        }
    });
}

第二个 Activity :

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main2);
    Intent intent = getIntent();
    String Höhe = intent.getExtras().getString("HöheName");
    String Länge = intent.getExtras().getString( "längeName");

    double höhe = Double.valueOf(Höhe);
    double länge = Double.valueOf(Länge);

    double längemalhöhe = höhe + länge;

    String ergebnis = new Double(längemalhöhe).toString();

    TextView Test = (TextView) findViewById(R.id.Test);

    Test.setText(ergebnis);

    Button weiter = (Button) findViewById(R.id.weiter2);
    weiter.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = getIntent();
            String Höhe = intent.getExtras().getString("HöheName");

            Intent i = new Intent(getApplicationContext(), Main3Activity.class);
            i.putExtra("HöheName", Höhe);
            startActivity(i);
        }
    });
}

第三个 Activity :

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main3);

    Intent intent = getIntent();
    String Höhe = intent.getExtras().getString("HöheName");

    TextView Test = (TextView) findViewById(R.id.Ergebnis2);

    Test.setText(Höhe);
}

这是 Logcat:

12-27 23:02:42.760 30997-30997/com.example.june.test E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.june.test, PID: 30997
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.june.test/com.example.june.test.Main2Activity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.trim()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3319)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
        at android.app.ActivityThread.access$1100(ActivityThread.java:229)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:7331)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.trim()' on a null object reference
        at java.lang.StringToReal.parseDouble(StringToReal.java:263)
        at java.lang.Double.parseDouble(Double.java:301)
        at java.lang.Double.valueOf(Double.java:338)
        at com.example.june.test.Main2Activity.onCreate(Main2Activity.java:22)
        at android.app.Activity.performCreate(Activity.java:6904)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3266)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415) 
        at android.app.ActivityThread.access$1100(ActivityThread.java:229) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:148) 
        at android.app.ActivityThread.main(ActivityThread.java:7331) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

Answer 1

我不知道这是否只是一个拼写错误，但你有这样一行:String Länge =intent.getExtras().getString(“längeName”);其中“längeName” 不是大写，但是，您最初是这样做的:i.putExtra( "LängeName", Länge); 其中 "LängeName" 是大写。所以问题可能是两个字符串不相同。当您尝试执行以下操作时:

String Länge = intent.getExtras().getString( "längeName");

字符串被初始化为 null，因为没有值分配给 "längeName"，如果尝试使用字符串。