如何为线性布局元素设置setLayoutParams

如何为LinearLayout元素设置setLayoutParams() 。 在MainActivity.java 。 我写了下面的代码设置布局参数和nullPointerException在第50行显示,我最后粘贴Logcat文件。

 layoutParams = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, 50); imageview1.setLayoutParams(layoutParams); // line no 50 layoutParams = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, 50); textview1.setLayoutParams(layoutParams); layoutParams = new LinearLayout.LayoutParams(LayoutParams.FILL_PARENT,LayoutParams.WRAP_CONTENT); listview01.setLayoutParams(layoutParams); 

这是我的xml文件

 <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="wrap_content" android:layout_height="wrap_content" android:stackFromBottom="true" > <ImageView android:id="@+id/imageview1" android:layout_width="wrap_content" android:layout_height="50px" android:background="@drawable/applicationbar" android:layout_x="0px" android:layout_y="0px" > </ImageView> <TextView android:id="@+id/textview1" android:layout_width="wrap_content" android:layout_height="50px" android:text="TextView" android:layout_x="0px" android:layout_y="55px" > </TextView> <ListView android:id="@+id/ListView01" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginLeft="10px" android:layout_marginRight="10px" android:layout_marginTop="35px" android:layout_marginBottom="40px" android:paddingLeft="0px" android:paddingRight="0px" /> </LinearLayout> 

日志猫:

 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): Uncaught handler: thread main exiting due to uncaught exception 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android/com.android.Listview}: java.lang.NullPointerException 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at android.app.ActivityThread.access$2200(ActivityThread.java:119) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at android.os.Handler.dispatchMessage(Handler.java:99) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at android.os.Looper.loop(Looper.java:123) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at android.app.ActivityThread.main(ActivityThread.java:4363) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at java.lang.reflect.Method.invokeNative(Native Method) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at java.lang.reflect.Method.invoke(Method.java:521) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at dalvik.system.NativeStart.main(Native Method) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): Caused by: java.lang.NullPointerException 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at com.android.Listview.onCreate(Listview.java:40) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 04-19 16:47:22.221: ERROR/AndroidRuntime(3437): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459) 

Solutions Collecting From Web of "如何为线性布局元素设置setLayoutParams"

 imageview1.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT, 50)); textview1.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT, 50)); listview01.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.WRAP_CONTENT)); 

在你的活动开始时尝试这个onCreate (尽pipe应该replace图片)。 不要忘记评论默认的setContentView

 // setContentView(R.layout.activity_main); TextView label = new TextView(this); label.setText("This is working, congrats!"); label.setTextSize(20); label.setGravity(Gravity.CENTER_HORIZONTAL); LinearLayout ll = new LinearLayout(this); ll.setOrientation(LinearLayout.VERTICAL); ll.setLayoutParams(new WindowManager.LayoutParams()); ll.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.MATCH_PARENT)); ll.setGravity(Gravity.CENTER); ll.addView(label); setContentView(ll);