Question

我必须以编程方式向线性布局添加按钮。但程序部队关闭了。这是我正在尝试的代码：

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

        LinearLayout ll = (LinearLayout) findViewById(R.id.vertic);
        Button button = new Button(this.getApplicationContext());
        LinearLayout.LayoutParams params = (LayoutParams) button.getLayoutParams();
        params.weight = 1;
        button.setText("MR. ABC");
        button.setLayoutParams(params);
        ll.addView(button, params);

    }

这是LogCat：

04-13 22:16:44.484: D/dalvikvm(12596): GC_EXTERNAL_ALLOC freed 70K, 50% free 2698K/5379K, external 2013K/2108K, paused 53ms
04-13 22:16:46.000: D/AndroidRuntime(12596): Shutting down VM
04-13 22:16:46.000: W/dalvikvm(12596): threadid=1: thread exiting with uncaught exception (group=0x40015578)
04-13 22:16:46.011: E/AndroidRuntime(12596): FATAL EXCEPTION: main
04-13 22:16:46.011: E/AndroidRuntime(12596): java.lang.RuntimeException: Unable to start activity ComponentInfo{maju.project.tourguide/maju.project.tourguide.RemoveContact}: java.lang.NullPointerException
04-13 22:16:46.011: E/AndroidRuntime(12596):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
04-13 22:16:46.011: E/AndroidRuntime(12596):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
04-13 22:16:46.011: E/AndroidRuntime(12596):    at android.app.ActivityThread.access$1500(ActivityThread.java:117)
04-13 22:16:46.011: E/AndroidRuntime(12596):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
04-13 22:16:46.011: E/AndroidRuntime(12596):    at android.os.Handler.dispatchMessage(Handler.java:99)
04-13 22:16:46.011: E/AndroidRuntime(12596):    at android.os.Looper.loop(Looper.java:123)
04-13 22:16:46.011: E/AndroidRuntime(12596):    at android.app.ActivityThread.main(ActivityThread.java:3687)
04-13 22:16:46.011: E/AndroidRuntime(12596):    at java.lang.reflect.Method.invokeNative(Native Method)
04-13 22:16:46.011: E/AndroidRuntime(12596):    at java.lang.reflect.Method.invoke(Method.java:507)
04-13 22:16:46.011: E/AndroidRuntime(12596):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:842)
04-13 22:16:46.011: E/AndroidRuntime(12596):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
04-13 22:16:46.011: E/AndroidRuntime(12596):    at dalvik.system.NativeStart.main(Native Method)
04-13 22:16:46.011: E/AndroidRuntime(12596): Caused by: java.lang.NullPointerException
04-13 22:16:46.011: E/AndroidRuntime(12596):    at maju.project.tourguide.RemoveContact.onCreate(RemoveContact.java:31)
04-13 22:16:46.011: E/AndroidRuntime(12596):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-13 22:16:46.011: E/AndroidRuntime(12596):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
04-13 22:16:46.011: E/AndroidRuntime(12596):    ... 11 more

有人可以说明问题吗？提前致谢

这是XML文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="@drawable/car_wallpaper"
    android:paddingLeft="16dp"
    android:paddingRight="16dp"
    android:id="@+id/vertic"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Your Emergency Contacts"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:textColor="#FFFF" />

</LinearLayout>

Answer 1

在这里：

 Button button = new Button(this.getApplicationContext()); //<<<

您正在传递Application上下文，用于创建无效上下文的动态按钮，因为您要将Button添加到当前Activity布局，因此您需要传递当前Activity上下文以进行创建按钮。将您的代码更改为：

     Button button = new Button(this);
     LinearLayout.LayoutParams params = 
          new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT,
                                      LinearLayout.LayoutParams.WRAP_CONTENT);
     params.weight = 1;
     button.setText("MR. ABC");
     button.setLayoutParams(params);
     ....

OR

Button button = new Button(Your_Current_Activity.this);
.....

并确保您在vertic

中传递的当前活动布局中包含setContentView id的布局

Answer 2

NullPointerException的原因是因为这一行：

LinearLayout.LayoutParams params = (LayoutParams) button.getLayoutParams();

在这里你得到 params = null ，因此在下一行中你会得到例外。

如果您想在按钮中使用LayoutParams，则首先需要对其进行初始化。这是您修改后的代码：

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

    LinearLayout ll = (LinearLayout) findViewById(R.id.vertic);
    Button button = new Button(this.getApplicationContext());
    LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
    params.weight = 1;
    button.setText("MR. ABC");
    button.setLayoutParams(params);
    ll.addView(button, params);
}

向LinearLayout添加按钮时出错

2 个答案: