Question

当我尝试做的时候：button.setHeight(900)

因此发生了以下错误：

java.lang.RuntimeException：无法启动活动 java.lang.NullPointerException：尝试调用虚方法'void android.widget.Button.setHeight（int）'在空对象引用上 android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2423）在 android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2483）在android.app.ActivityThread.access $ 900（ActivityThread.java:153）at android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1349）在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）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:628）引起：java.lang.NullPointerException：尝试调用虚拟 null对象上的方法'void android.widget.Button.setHeight（int）' 参考 com.codeduc.aayushman.apps.htmlviewerpro.MainActivity.onCreate（MainActivity.java:100）在android.app.Activity.performCreate（Activity.java:6303）at android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1108）在 android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2376）

请告诉我们如何修理它。

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

您的按钮变量为空，请尝试使用findviewbyId

进行初始化

Android按钮setHeight（）错误

2 个答案: