Android 编辑文本问题

我是java新手，在将“输入”转换为字符串时遇到问题

input = (EditText) findViewById(R.id.wpiszZapytanie);
String zapytanieDoUrl = input.getText().toString();

它与此日志一起崩溃：

10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{eu.qm.mood/eu.qm.mood.GIFActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2658)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2723)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.app.ActivityThread.access$900(ActivityThread.java:172)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:145)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5832)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:372)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at eu.qm.mood.GIFActivity.onCreate(GIFActivity.java:18)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.app.Activity.performCreate(Activity.java:6221)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2611)
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2723) 
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.app.ActivityThread.access$900(ActivityThread.java:172) 
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422) 
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102) 
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:145) 
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5832) 
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method) 
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:372) 
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) 
10-10 23:57:48.589 9423-9423/eu.qm.mood E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) 

正如我所看到的，某处没有任何东西（空）。我理解这段代码无法看到文本框中的内容，以及用户键入的内容

Edittext位于content_main.xml中

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:showIn="@layout/activity_main" tools:context=".MainActivity">

    <TextView android:text="@string/welcome" android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="20dp"
        android:textColor="@color/colorAccent"
        android:textStyle="bold"
        android:fontFamily="Roboto"
        android:id="@+id/textView2"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/wpiszZapytanie"
        android:singleLine="true"
        android:layout_below="@+id/textView2"
        android:layout_alignParentStart="true"
        android:layout_alignParentEnd="true"
        android:inputType="text"/>

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/go"
        android:id="@+id/doit"
        android:onClick="goClick"
        android:layout_below="@+id/wpiszZapytanie"
        android:layout_centerHorizontal="true" />
</RelativeLayout>

这里是activity_gif.xml

<?xml version="1.0" encoding="utf-8"?>
<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:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context="eu.qm.mood.GIFActivity">

    <WebView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/GifResulttwo"
        android:layout_alignParentStart="true"
        android:layout_alignParentBottom="true"
        android:layout_alignParentEnd="true"
        android:layout_below="@+id/editText" />
</RelativeLayout>

<?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" >
        <EditText 
            android:id="@+id/wpiszZapytanie"/>    

    </LinearLayout>

---

您的

输入

变量为空，这就是您得到异常的原因

可能的原因：

• 我认为您在编辑文本时使用了错误的

  id

  。检查xml中是否有id为wpiszZapytanie的

  EditText

  元素
• 您可能正在扩展错误的xml布局，该布局没有id为wpiszZapytanie的

  EditText

• 您可能正在执行

  findViewById（R.id.wpiszZapytanie）setContentView（）之前的code>

---

正如pgitu指出的那样：输入为空，当findViewById查找无法找到它要查找的内容时，就会发生这种情况。造成这种情况的一个主要原因是在调用setContentView之前调用此

---

在设置UI之前，无法访问UI元素。所以如果上面这两个不是，也许这是

确保您的活动在onCreate方法上遵循此逻辑

public class GIFActivity extends Activity {
EditText input;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState); //First
        setContentView(R.layout.activity_gif);//Second
        input = (EditText) findViewById(R.id.wpiszZapytanie);//Third

        String text = input.getText().toString();
    }   
}

activity_gif.xml

<?xml version="1.0" encoding="utf-8"?>
<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:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context="eu.qm.mood.GIFActivity">

    <WebView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/GifResulttwo"
        android:layout_alignParentStart="true"
        android:layout_alignParentBottom="true"
        android:layout_alignParentEnd="true"
        android:layout_below="@+id/editText" />
</RelativeLayout>

<?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" >
        <EditText 
            android:id="@+id/wpiszZapytanie"/>    

    </LinearLayout>

你能发布你的xml吗？我认为EditText视图本身由于某种原因是空的。你确定你的布局已经膨胀了吗？我没有提到edittext“wpiszZapytanie”在content\u main.xml中而不是“activity\u gif.xml”我只是假设它的名称是“activity\u gif.xml”。您应该发布您的XML，以便我们能够更好地评估您的问题所在。