錯誤試圖更改密碼提示字體

Question

我試圖跟蹤該post建議：

但是當我運行此代碼，我的程序崩潰。這裏是我的代碼：

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    /* Change the font for the password hint to match that of the 
    * user name field */ 
    EditText pw = (EditText) findViewById(R.id.password); 
    pw.setTypeface(Typeface.DEFAULT); //<---Crashes on this line 
    pw.setTransformationMethod(new PasswordTransformationMethod()); 

    setContentView(R.layout.activity_main); 
} 

下面是此對象的XML：

<EditText 
    android:id="@+id/password" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignLeft="@+id/userName" 
    android:layout_alignRight="@+id/appName" 
    android:layout_below="@+id/userName" 
    android:layout_marginTop="14dp" 
    android:ems="10" 
    android:hint="@string/password" 
    android:inputType="textPassword" /> 

最後，這裏是logcat的輸出，我可以看到錯誤：

05-09 00:30:21.408: E/Trace(16987): error opening trace file: No such file or directory (2) 05-09 00:30:21.918: D/AndroidRuntime(16987): Shutting down VM 05-09 00:30:21.918: W/dalvikvm(16987): threadid=1: thread exiting with uncaught exception (group=0x40a71930) 05-09 00:30:21.978: E/AndroidRuntime(16987): FATAL EXCEPTION: main 05-09 00:30:21.978: E/AndroidRuntime(16987): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mobilenicity.gen_co_event_marketing_app/com.mobilenicity.gen_co_event_marketing_app.MainActivity}: java.lang.NullPointerException 05-09 00:30:21.978: E/AndroidRuntime(16987): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 05-09 00:30:21.978: E/AndroidRuntime(16987): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 05-09 00:30:21.978: E/AndroidRuntime(16987): at android.app.ActivityThread.access$600(ActivityThread.java:141) 05-09 00:30:21.978: E/AndroidRuntime(16987): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 05-09 00:30:21.978: E/AndroidRuntime(16987): at android.os.Handler.dispatchMessage(Handler.java:99) 05-09 00:30:21.978: E/AndroidRuntime(16987): at android.os.Looper.loop(Looper.java:137) 05-09 00:30:21.978: E/AndroidRuntime(16987): at android.app.ActivityThread.main(ActivityThread.java:5041) 05-09 00:30:21.978: E/AndroidRuntime(16987): at java.lang.reflect.Method.invokeNative(Native Method) 05-09 00:30:21.978: E/AndroidRuntime(16987): at java.lang.reflect.Method.invoke(Method.java:511) 05-09 00:30:21.978: E/AndroidRuntime(16987): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 05-09 00:30:21.978: E/AndroidRuntime(16987): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 05-09 00:30:21.978: E/AndroidRuntime(16987): at dalvik.system.NativeStart.main(Native Method) 05-09 00:30:21.978: E/AndroidRuntime(16987): Caused by: java.lang.NullPointerException 05-09 00:30:21.978: E/AndroidRuntime(16987): at com.mobilenicity.gen_co_event_marketing_app.MainActivity.onCreate(MainActivity.java:26) 05-09 00:30:21.978: E/AndroidRuntime(16987): at android.app.Activity.performCreate(Activity.java:5104) 05-09 00:30:21.978: E/AndroidRuntime(16987): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 05-09 00:30:21.978: E/AndroidRuntime(16987): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 05-09 00:30:21.978: E/AndroidRuntime(16987): ... 11 more

燦弄清楚發生了什麼問題。任何人都可以看到它嗎？謝謝！

Answer 1

變化setContentView(R.layout.activity_main);

通話說它剛過super.onCreate(savedInstanceState);

---

當你在做 EditText pw = (EditText) findViewById(R.id.password);， findViewById 「無法檢索」 你是在已定義的 EditText您 layout（因爲你在之後調用 setContentView）所以 findViewById返回null，當你在做 pw.setTypeface(Typeface.DEFAULT);時它會拋出 NPE，因爲pw是 null。