Question

我正在使用我的andorid应用程序遇到一些问题我目前正在eclipse包中开发。我想在点击按钮上进行简单的文本更改，但遗憾的是，当我在设备上运行应用程序时，它会停止工作。应用程序在我的设备上崩溃，但在eclipse中没有错误。

这是我的代码：

final TextView chores = (TextView) findViewById(R.id.chores);
Button choreButton = (Button) findViewById(R.id.choreButton);

View.OnClickListener listener = new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        String next = "Go make some Coffee.";
        chores.setText(next);
    }
};
choreButton.setOnClickListener(listener);

感谢您的帮助！：）

所以这是XML文件

   <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.zargi.choreme.MainActivity$PlaceholderFragment"
        android:background="#6EFF70" >

        <TextView
            android:id="@+id/choremehead"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Are you bored? Then go and..."
            android:textSize="22sp"
            android:textColor="#ffffff" />

        <TextView
            android:id="@+id/chores"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignLeft="@+id/choremehead"
            android:layout_centerVertical="true"
            android:text="@string/chore"
            android:textColor="@color/textColor"
            android:textSize="22sp" />

        <Button
            android:id="@+id/choreButton"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignLeft="@+id/chores"
            android:layout_alignParentBottom="true"
            android:background="#ffffff"
            android:text="Enlighten me!" />

    </RelativeLayout>

这就是我在java中写的

import android.app.Activity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final TextView chores = (TextView) findViewById(R.id.chores);
        Button choreButton = (Button) findViewById(R.id.choreButton);

        View.OnClickListener listener = new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String next = "Go make some Coffee.";
                chores.setText(next);
            }
        };
        choreButton.setOnClickListener(listener);
    }
}

这里是logcat，现在有一些错误在之前没有...

09-02 04:48:06.650: D/AndroidRuntime(972): Shutting down VM
09-02 04:48:06.650: W/dalvikvm(972): threadid=1: thread exiting with uncaught exception (group=0xb2a9dba8)
09-02 04:48:06.670: E/AndroidRuntime(972): FATAL EXCEPTION: main
09-02 04:48:06.670: E/AndroidRuntime(972): Process: com.zargi.choreme, PID: 972
09-02 04:48:06.670: E/AndroidRuntime(972): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.zargi.choreme/com.zargi.choreme.MainActivity}: java.lang.NullPointerException
09-02 04:48:06.670: E/AndroidRuntime(972):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
09-02 04:48:06.670: E/AndroidRuntime(972):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
09-02 04:48:06.670: E/AndroidRuntime(972):  at android.app.ActivityThread.access$800(ActivityThread.java:135)
09-02 04:48:06.670: E/AndroidRuntime(972):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
09-02 04:48:06.670: E/AndroidRuntime(972):  at android.os.Handler.dispatchMessage(Handler.java:102)
09-02 04:48:06.670: E/AndroidRuntime(972):  at android.os.Looper.loop(Looper.java:136)
09-02 04:48:06.670: E/AndroidRuntime(972):  at android.app.ActivityThread.main(ActivityThread.java:5017)
09-02 04:48:06.670: E/AndroidRuntime(972):  at java.lang.reflect.Method.invokeNative(Native Method)
09-02 04:48:06.670: E/AndroidRuntime(972):  at java.lang.reflect.Method.invoke(Method.java:515)
09-02 04:48:06.670: E/AndroidRuntime(972):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
09-02 04:48:06.670: E/AndroidRuntime(972):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
09-02 04:48:06.670: E/AndroidRuntime(972):  at dalvik.system.NativeStart.main(Native Method)
09-02 04:48:06.670: E/AndroidRuntime(972): Caused by: java.lang.NullPointerException
09-02 04:48:06.670: E/AndroidRuntime(972):  at com.zargi.choreme.MainActivity.onCreate(MainActivity.java:38)
09-02 04:48:06.670: E/AndroidRuntime(972):  at android.app.Activity.performCreate(Activity.java:5231)
09-02 04:48:06.670: E/AndroidRuntime(972):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
09-02 04:48:06.670: E/AndroidRuntime(972):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
09-02 04:48:06.670: E/AndroidRuntime(972):  ... 11 more
09-02 04:48:48.726: I/Process(972): Sending signal. PID: 972 SIG: 9

androidManifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.zargi.choreme"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="14"
        android:targetSdkVersion="19" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.zargi.choreme.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

据说我没有看到logcat中的任何错误，但我的应用程序在移动电话上崩溃，就像在AVD上一样。我也是java编程的新手，很抱歉，如果我犯了任何愚蠢的错误：D

Answer 1

这里有几个选项

chores是null
choreButton是null

在Android中插入日志语句，最好是通过框架或Log.d(String, String)（甚至是好的System.out.println(String)作品）。

像

Log.d("nullcheck", "chores?" + (chores == null) + " chorebutton?" + (choreButton == null));

但是，您可能会尝试在setContentView()中初始化之前的视图<！> onCreate()。就像下面这样，你很好（如果，并且只有当你的xml正确充气，并且id存在于xml上）

public class MyActivity extends Activity {
    TextView chores;
    Button choreButton;

    public void onCreate(Bundle b) {
        super.onCreate(b);
        setContentView(R.layout.activity_main);
        chores = (TextView)findViewById(R.id.chores);
        choreButton = (Button)findViewById(R.id.choreButton);

        //Here a log statement. Insert it in your code, run the app, and examine the output
        Log.d("nullcheck", "chores?" + (chores == null) + " chorebutton?" + (choreButton == null));

        View.OnClickListener listener = new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String next = "Go make some Coffee.";
                chores.setText(next);
            }
        };
        choreButton.setOnClickListener(listener);
    }
}

话虽如此，必须在xml中声明了R.id.chores和R.id.choreButton（在我的示例activity_main.xml中）

<LinearLayout
    ... >
    <TextView
        android:id="@+id/chores"
        ... />
    <Button
        android:id="@+id/choreButton"
        ... />
</LinearLayout>

Answer 2

确定。因此，必须检查Button和TextView是否在activity_main.xml文件中。

eclipse按钮点击更改文本

2 个答案: