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[英]NullPointerException from button.setOnClickListener()
[英]DialogFragment: button.setOnClickListener throws NullPointerException
我有一個帶有這樣的按鈕的活動:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:onClick="onButtonClickListener"
android:text="Show Fragment" />
</RelativeLayout>
而我的xml中的onButtonClickListener方法是(在這里,我創建DialogFragment並將onClickListener設置為對話框中的清除按鈕):
public void onButtonClickListener(View view) {
FragmentManager fm = getFragmentManager();
MyDialogFragment dialogFragment = new MyDialogFragment ();
dialogFragment.show(fm, "Sample Fragment");
final EditText messageText = (EditText) findViewById(R.id.editText);
Button clearButton = (Button) findViewById(R.id.button_clear);
clearButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
messageText.setText(null);
}
});
}
我的問題是,當DialogFragment顯示它拋出NullPointerException時:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.cristi.dialogfragmenttest2.MainActivity.onButtonClickListener(MainActivity.java:51)
在這一行代碼中: clearButton.setOnClickListener(new View.OnClickListener() {
我的DialogFragment XML是:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<EditText
android:id="@+id/editText"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:maxLength="200" />
<Button
android:id="@+id/button_clear"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Clear"
android:layout_below="@+id/editText"
android:layout_centerHorizontal="true" />
</RelativeLayout>
setOnClickListener可能是什么問題? 為什么說我來自DialogFragment的按鈕為空?
歡迎任何參考或建議! 提前致謝!
編輯:
-MyDialogFragment代碼:
public class MyDialogFragment extends DialogFragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.dialog_fragment, container, false);
getDialog().setTitle("Enter message");
return rootView;
}
您必須引用根目錄按鈕的根視圖,其中按鈕button_clear
,然后調用rootView.findViewById(...)
以獲取按鈕引用...解決方案:
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.dialog_fragment, container, false);
getDialog().setTitle("Enter message");
Button clearButton = (Button) rootView.findViewById(R.id.button_clear);
clearButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
messageText.setText(null);
}
});
return rootView;
}
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