Double.parseDouble(EditText)总是抛出NUllPointerException.如何解决

Question

我想从EditText中获得一个双值，其中只能输入numberDecimal和numberSigned。

我想：

EditText editText1 = (EditText)findViewById(R.id.edittext1)
double double1 = Double.parseDouble(editText1.getText().toString());

但是logcat说这个double = ""和应用程序崩溃了

Logcat:

08-29 20:52:24.148  22688-22688/test.com.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity  
ComponentInfo{test.com.app/test.com.app.Main}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2295)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)
        at android.app.ActivityThread.access$700(ActivityThread.java:159)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:176)
        at android.app.ActivityThread.main(ActivityThread.java:5419)
        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:1046)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.NullPointerException
        at java.lang.StringToReal.parseDouble(StringToReal.java:244)
        at java.lang.Double.parseDouble(Double.java:295)
        at test.com.app.Graph.yWerte(Graph.java:188)
        at test.com.app.Graph.getDataFromReceiver(Graph.java:184)
        at test.com.app.Main.onCreate(Main.java:30)
        at android.app.Activity.performCreate(Activity.java:5372)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)       
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2257)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)
        at android.app.ActivityThread.access$700(ActivityThread.java:159)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:176)
        at android.app.ActivityThread.main(ActivityThread.java:5419)
        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:1046)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862)
        at dalvik.system.NativeStart.main(Native Method)

Answer 1

editText1.getText()就是null。试试这个：

CharSequence cs = editText1.getText();
double double1 = cs == null ? -1.0 : Double.parseDouble(cs.toString());

如果你想在键入不可解析的双精度时也避免NumberFormatException，你可以写：

double double1 = -1.0; // invalid!
try {
    double1 = Double.parseDouble(editText1.getText().toString());
} catch(RuntimeException ignored) {
    // NPE or parsing failed, double1 == -1.0
}

捕获（同时忽略）RuntimeException s通常不是一个好的做法，但由于特定的API，在本例中可以。

编辑：在发布后更新堆栈跟踪

编辑2：更新以更正解析问题