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我正在尝试添加一个文本视图，并在尝试将其添加到布局时不断获得一个nullPointer。
我的布局：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/app_header" android:layout_width="match_parent"
android:layout_height="@dimen/headerSize" android:background="@color/iPhoneBackground">
<View
android:layout_width="match_parent"
android:layout_height="1dp"
android:background="@color/grey"
android:layout_alignParentBottom="true" />
</RelativeLayout>
我的班级：
public class AppHeader extends RelativeLayout {
Context mContext;
screenName sName;
RelativeLayout parent;
public AppHeader(Context context, screenName sn) {
super(context);
mContext = context;
sName = sn;
parent = (RelativeLayout) findViewById(R.id.app_header);
init();
}
public AppHeader(Context context, AttributeSet attrs, int defStyle)
{
super(context, attrs, defStyle);
mContext = context;
init();
}
public AppHeader(Context context, AttributeSet attrs) {
super(context, attrs);
mContext = context;
init();
}
public void init(){
RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
TextView title = new TextView(mContext);
switch (sName) {
case FAVORITER:
title.setText(mContext.getString(R.string.favourite));
break;
case SOKRESA:
title.setText(mContext.getString(R.string.search));
break;
case REALTID:
// tod
break;
case STORNINGAR:
// tod
break;
case MER:
// tod
break;
}
params.addRule(RelativeLayout.CENTER_HORIZONTAL, RelativeLayout.TRUE);
params.addRule(RelativeLayout.ALIGN_PARENT_TOP, RelativeLayout.TRUE);
title.setLayoutParams(params);
parent.addView(title);
}
}
Logcat在最后一行"parent.addView（title）；"上给了我一个nullPointer
有人知道我做错了什么吗？
这是logcat：
java.lang.RuntimeException: Unable to start activity ComponentInfo{mtr.se.reskoll/mtr.se.reskoll.SokResa}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
at android.app.ActivityThread.access$600(ActivityThread.java:141)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5041)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at mtr.se.reskoll.AppHeader.init(AppHeader.java:63)
at mtr.se.reskoll.AppHeader.<init>(AppHeader.java:24)
at mtr.se.reskoll.SokResa.setHeader(SokResa.java:50)
at mtr.se.reskoll.SokResa.onCreate(SokResa.java:37)
at android.app.Activity.performCreate(Activity.java:5104)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
at android.app.ActivityThread.access$600(ActivityThread.java:141)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5041)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
parent"变量仅在构造函数public AppHeader(Context context, screenName sn)中初始化。如果使用其他构造函数，parent将为null。
必须在init()方法中移动行parent = (RelativeLayout) findViewById(R.id.app_header);。
试试这个：
Activity activity = (Activity) mContext;
parent = (RelativeLayout) activity.findViewById(R.id.app_header);
public AppHeader(Context context) {
super(context);
mContext = context;
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
parent = (MobileAndrRelativeLayout) inflater.inflate(R.layout.yourlayout, this);
init();
}
public AppHeader(Context context, AttributeSet attrs, int defStyle)
{
super(context, attrs, defStyle);
mContext = context;
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
parent = (MobileAndrRelativeLayout) inflater.inflate(R.layout.yourlayout, this);
init();
}
public AppHeader(Context context, AttributeSet attrs) {
super(context, attrs);
mContext = context;
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
parent = (MobileAndrRelativeLayout) inflater.inflate(R.layout.yourlayout, this);
init();
}
编辑：要显示文本，这取决于您使用的构造函数，因为您只在第一个构造函数中设置文本。
我建议采用不同的方法：（我还修改了第一个构造函数）
public void SetTitle(sName)
{
switch (sName) {
case FAVORITER:
title.setText(mContext.getString(R.string.favourite));
break;
case SOKRESA:
title.setText(mContext.getString(R.string.search));
break;
case REALTID:
// tod
break;
case STORNINGAR:
// tod
break;
case MER:
// tod
break;
}
}
public void init(){
RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
TextView title = new TextView(mContext);
// we will add this line for test, to see in the problem is that the text is not displayed or the textview itself is not visible
title.setBackgroundColor(Color.YELLOW);
params.addRule(RelativeLayout.CENTER_HORIZONTAL, RelativeLayout.TRUE);
params.addRule(RelativeLayout.ALIGN_PARENT_TOP, RelativeLayout.TRUE);
title.setLayoutParams(params);
parent.addView(title);
}
因此，在您创建自定义视图后：
AppHeader header= new AppHeader (context);
header.SetTitle("Test");
此外，为了确保开关正常工作（也就是说，你正在发送一个实际包含在开关选项中的屏幕名称），请尝试一种简单的测试方法，而不是上面的方法：
public void SetTitle(sName)
{
title.setText("Test Title");
}