在TextView中设置文本会引发空指针异常

时间:2014-06-17 15:16:18

标签: java android nullpointerexception textview

我刚开始进行android编程,我在尝试在TextView中设置文本时遇到了这个错误。我研究过其他人的问题,但我似乎已经照顾到他们的答案所指出的麻烦问题。

这是我的XML代码:

<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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.everythingmath.MainActivity$PlaceholderFragment" >

<GridLayout
    android:id="@+id/problemLayout"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerInParent="true"
    android:columnCount="5"
    android:rowCount="1" >

    <TextView 
        android:id="@+id/firstNumber"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="First Number"
        android:textSize="20sp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=" + "
        android:textSize="30sp" />

    <TextView 
        android:id="@+id/secondNumber"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Second Number"
        android:textSize="20sp" />

    <EditText
        android:id="@+id/numTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="number" 
        android:hint="Text Goes Here"
        android:textSize="20sp"/>

</GridLayout>
</RelativeLayout>

这是我的相关Java:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

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

    int firstNumber = createRandomNumber(10);
    int secondNumber = createRandomNumber(10);
    TextView firstNumText = (TextView)findViewById(R.id.firstNumber);
    TextView secondNumText = (TextView)findViewById(R.id.secondNumber);
    firstNumText.setText(Integer.toString(firstNumber));
    secondNumText.setText(Integer.toString(secondNumber));
}

我尝试设置引发错误的文本的行。随机数生成器也可以正常工作。

1 个答案:

答案 0 :(得分:0)

PlaceholderFragment类中对MainActivity类进行本地化。

public View onCreateView方法更改为

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_main, container, false);

    int firstNumber = createRandomNumber(10);
    int secondNumber = createRandomNumber(10);
    TextView firstNumText = (TextView)findViewById(R.id.firstNumber);
    TextView secondNumText = (TextView)findViewById(R.id.secondNumber);
    firstNumText.setText(Integer.toString(firstNumber));
    secondNumText.setText(Integer.toString(secondNumber));

    return rootView;
}

您可能需要将createRandomNumber方法移至PlaceholderFragment课程。如果您已将Fragment的名称从fragment_main更改为其他内容,请在此行中更改

View rootView = inflater.inflate(R.layout.fragment_main, container, false);

您当前的代码无效,因为内部

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    [..]
}

您只能通过在findViewById布局中声明的ID视图(activity_main)找到。您的TextView视图可能在fragment_main布局中声明。