EditText 一直返回 null? [英] EditText keeps returning null?

问题描述

public class Input extends FragmentActivity {

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


    EditText mEditText1 = (EditText)findViewById(R.id.number1i); 
    String val1 = mEditText1.getText().toString();
    EditText mEditText2 = (EditText)findViewById(R.id.number2i); 
    String val2 = mEditText2.getText().toString();

    double dVal1 = Double.parseDouble(val1); 
    double dVal2 = Double.parseDouble(val2);


  } 
}

这是我的 xml 文件:

This is my xml file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" 
    android:background="@drawable/background">

    <EditText
        android:id="@+id/number1i"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Enter your first value"
        android:inputType="numberDecimal" />   

    <EditText
        android:id="@+id/number2i"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Enter your second value"
        android:inputType="numberDecimal" />

    <TextView
        android:id="@+id/output"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:textSize="22sp" />

    <Button
        android:id="@+id/add_marker"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp"
        android:text="Add value"
        android:onClick="userInput1"
        android:textSize="22sp" />   

</LinearLayout>

错误:

12-05 08:57:17.113: E/AndroidRuntime(8420): Caused by: java.lang.NullPointerException
12-05 08:57:17.113: E/AndroidRuntime(8420):     at com.example.whatever.input.onCreate(input.java:23)

第 23 行是

String val1 = mEditText1.getText().toString();

有什么帮助吗?

我认为是因为该值可能为空?

I would presume because the value could be empty?

推荐答案

在您的代码中 mEditText1.getText() 在 onCreate 中将始终为空，除非您必须设置text 来自 XML

In your code mEditText1.getText() will always be empty in onCreate unless you have to set text in it from XML

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