Question

我对发生的事情感到有些困惑......

当EditText id = username时，似乎应用程序运行良好。

但是当我更改了图片中的ID时，应用会停止并产生下面的错误。

我的XML：

 <?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"
android:background="@drawable/blurred">
<include
    android:id="@+id/toolbarSignup"
    layout="@layout/toolbar_layout" />
<ImageView
    android:layout_width="100dp"
    android:layout_height="100dp"
    android:id="@+id/userPic"
    android:src="@drawable/ic_upload"
    android:layout_below="@+id/toolbarSignup"
    android:layout_centerHorizontal="true" />
<Button
    style="?android:attr/buttonStyleSmall"
    android:layout_width="130dp"
    android:layout_height="40dp"
    android:text="Upload Image"
    android:id="@+id/upload"
    android:layout_below="@+id/userPic"
    android:layout_centerHorizontal="true"
    android:background="#03A9F4"
    android:alpha="0.50"/>
<EditText
    android:layout_width="230dp"
    android:layout_height="wrap_content"
    android:inputType="textPersonName"
    android:id="@+id/firstname"
    android:layout_below="@+id/upload"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="20dp"
    android:hint="First Name" />

我的logcat：

02-17 07:05:42.756 17367-17367/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: glorioso.david.metrohomes, PID: 17367
java.lang.RuntimeException: Unable to start activity ComponentInfo{glorioso.david.metrohomes/glorioso.david.metrohomes.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5021)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:827)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:643)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.support.v7.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:98)
at android.support.v7.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:91)
at android.support.v7.app.ToolbarActionBar.<init>(ToolbarActionBar.java:73)
at android.support.v7.app.AppCompatDelegateImplV7.setSupportActionBar(AppCompatDelegateImplV7.java:205)
at android.support.v7.app.AppCompatActivity.setSupportActionBar(AppCompatActivity.java:99)
at glorioso.david.metrohomes.MainActivity.onCreate(MainActivity.java:27)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1090)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245) 
at android.app.ActivityThread.access$800(ActivityThread.java:135) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:136) 
at android.app.ActivityThread.main(ActivityThread.java:5021) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:515) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:827) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:643) 
at dalvik.system.NativeStart.main(Native Method)

我的活动：

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;

public class Signup extends AppCompatActivity {

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

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbarSignup);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("Registration");
    }
}

Answer 1

您可能忘记更改onCreate方法中的ID。将findViewById(R.id.username);更改为findViewById(R.id.firstname);

希望这能解决你的问题。

Answer 2

如果您想使用id/firstname，则在您的活动onCreate method中应定义Edit Text name=(EditText)findViewById(R.id.firstname)。

注意到xml中的ID应始终与您的活动相同。

更改testView标识

2 个答案: