Unable to parsing got Null pointer Exception

问题

et2.addTextChangedListener(new TextWatcher() {

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
        // TODO Auto-generated method stub
        et2 = (EditText) findViewById(R.id.editText2);
        area = Math.PI * radius * radius;
        String name = Double.toString(area);
        et2.setText(name);

    }

    @Override
    public void beforeTextChanged(CharSequence s, int start, int count,
            int after) {
        // TODO Auto-generated method stub

    }

    @Override
    public void afterTextChanged(Editable s) {
        // TODO Auto-generated method stub

    }
});

01-31 19:05:01.346: D/AndroidRuntime(650): Shutting down VM 01-31 19:05:01.346: W/dalvikvm(650): threadid=1: thread exiting with uncaught exception (group=0x40015560) 01-31 19:05:01.366: E/AndroidRuntime(650): FATAL EXCEPTION: main 01-31 19:05:01.366: E/AndroidRuntime(650): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.zlistactivity/com.example.zlistactivity.MainActivity}: java.lang.NumberFormatException: 01-31 19:05:01.366: E/AndroidRuntime(650): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 01-31 19:05:01.366: E/AndroidRuntime(650): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 01-31 19:05:01.366: E/AndroidRuntime(650): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 01-31 19:05:01.366: E/AndroidRuntime(650): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 01-31 19:05:01.366: E/AndroidRuntime(650): at android.os.Handler.dispatchMessage(Handler.java:99) 01-31 19:05:01.366: E/AndroidRuntime(650): at android.os.Looper.loop(Looper.java:123) 01-31 19:05:01.366: E/AndroidRuntime(650): at android.app.ActivityThread.main(ActivityThread.java:3683) 01-31 19:05:01.366: E/AndroidRuntime(650): at java.lang.reflect.Method.invokeNative(Native Method) 01-31 19:05:01.366: E/AndroidRuntime(650): at java.lang.reflect.Method.invoke(Method.java:507) 01-31 19:05:01.366: E/AndroidRuntime(650): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 01-31 19:05:01.366: E/AndroidRuntime(650): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 01-31 19:05:01.366: E/AndroidRuntime(650): at dalvik.system.NativeStart.main(Native Method) 01-31 19:05:01.366: E/AndroidRuntime(650): Caused by: java.lang.NumberFormatException: 01-31 19:05:01.366: E/AndroidRuntime(650): at org.apache.harmony.luni.util.FloatingPointParser.parseDouble(FloatingPointParser.java:267) 01-31 19:05:01.366: E/AndroidRuntime(650): at java.lang.Double.parseDouble(Double.java:318) 01-31 19:05:01.366: E/AndroidRuntime(650): at java.lang.Double.valueOf(Double.java:356) 01-31 19:05:01.366: E/AndroidRuntime(650): at com.example.zlistactivity.MainActivity.onCreate(MainActivity.java:22) 01-31 19:05:01.366: E/AndroidRuntime(650): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 01-31 19:05:01.366: E/AndroidRuntime(650): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 01-31 19:05:01.366: E/AndroidRuntime(650): ... 11 more 01-31 19:05:05.156: I/Process(650): Sending signal. PID: 650 SIG: 9

回答1:

Declare your edittext before the Textchange listener :

et2 = (EditText) findViewById(R.id.editText2);
et2.addTextChangedListener(new TextWatcher() {
@Override
public void onTextChanged(CharSequence s, int start, int before, int count){
    // TODO Auto-generated method stub
    area = Math.PI * radius * radius;
    String name = Double.toString(area);
    et2.setText(name);
}

来源：https://stackoverflow.com/questions/14627264/unable-to-parsing-got-null-pointer-exception