Android Button setHeight（）错误

Question

When I am trying to do: button.setHeight(900)

So the following error occurred:

java.lang.RuntimeException: Unable to start activity java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setHeight(int)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2423) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2483) at android.app.ActivityThread.access$900(ActivityThread.java:153) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5438) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setHeight(int)' on a null object reference at com.codeduc .aayushman.apps.htmlviewerpro.MainActivity.onCreate(MainActivity.java:100) at android.app.Activity.performCreate(Activity.java:6303) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2376)

Please tell how to fix it.

Answer 1

Any component available in xml must be initialized in the respective activity file. Then only it is availablein the activity scope
Button button = (Button) findViewById(R.id.assetname);  //Need to declare
then we can do as follows
button.setHeight(100)
or more logically we can have as follows
int buttonWidth = (int) (screenWidth / 3.0);
RelativeLayout.LayoutParams params = (LayoutParams) button.getLayoutParams();
params.width = buttonWidth;
params.leftMargin = buttonWidth;
button.setLayoutParams(params);

Answer 2

您的button变量为null，请尝试使用findviewbyId对其进行初始化