Question

我尝试在填充表单中的每个字段后才启用按钮。为此，我使用了TextWatcher，但我一直收到错误。

我的contentView是activity_add_grade，而我的按钮和字段在我的fragment_add_grade xml中吗？我是新手，我不完全理解为什么这两个xml文件都是由ADT自动生成的。

代码：

public class AddClass extends ActionBarActivity {

int baseYear=2005;
int thisYear = Calendar.getInstance().get(Calendar.YEAR);
DBAdapter db = new DBAdapter(this);

private EditText editText1;
private EditText editText2;

public TextWatcher watcher = new TextWatcher(){

    @Override
    public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
    }

    @Override
    public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
        checkFieldsForEmptyValues();
    }

    @Override
    public void afterTextChanged(Editable editable) {
    }
};

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

    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment()).commit();
    }

    editText1 = (EditText) findViewById(R.id.editTitle);
    editText2 = (EditText) findViewById(R.id.editCredit);

    // Program aborts as soon as I try to add the listener to editText1
    editText1.addTextChangedListener(watcher);
    editText2.addTextChangedListener(watcher);

}

我的LogCat：

03-30 18:23:44.963: E/AndroidRuntime(1961): FATAL EXCEPTION: main
03-30 18:23:44.963: E/AndroidRuntime(1961): Process: com.NsouthProductions.gradetrackerpro, PID: 1961
03-30 18:23:44.963: E/AndroidRuntime(1961): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.NsouthProductions.gradetrackerpro/com.NsouthProductions.gradetrackerpro.AddClass}: java.lang.NullPointerException
03-30 18:23:44.963: E/AndroidRuntime(1961):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at android.os.Handler.dispatchMessage(Handler.java:102)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at android.os.Looper.loop(Looper.java:136)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at android.app.ActivityThread.main(ActivityThread.java:5017)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at java.lang.reflect.Method.invokeNative(Native Method)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at java.lang.reflect.Method.invoke(Method.java:515)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at dalvik.system.NativeStart.main(Native Method)
03-30 18:23:44.963: E/AndroidRuntime(1961): Caused by: java.lang.NullPointerException
03-30 18:23:44.963: E/AndroidRuntime(1961):     at com.NsouthProductions.gradetrackerpro.AddClass.onCreate(AddClass.java:63)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at android.app.Activity.performCreate(Activity.java:5231)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
03-30 18:23:44.963: E/AndroidRuntime(1961):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
03-30 18:23:44.963: E/AndroidRuntime(1961):     ... 11 more

Answer 1

您的activity_add_grade不包含带有id editTitle

的EditText

Answer 2

下面：

editText1 = (EditText) findViewById(R.id.editTitle);

看起来findViewById方法无法找到具有此ID的元素，因此返回null。

这就是为什么以后会在此行引发 NullPointerException 的原因：

editText1.addTextChangedListener(watcher);

==＆GT;将ID属性editTitle添加到布局activity_add_grade

内的EditText

TextChangedListener在我身上崩溃

2 个答案: