主要活动.java
package com.bandiapps.graphicfuture;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
private CustomView cv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
cv = findViewById(R.id.cus_1);
cv.setWidth();
}
}
自定义视图.java
package com.bandiapps.graphicfuture;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;
public class CustomView extends View {
int width,height;
private Paint paint;
public CustomView(Context context, AttributeSet attrs) {
super(context);
paint = new Paint();
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
width = w;
height = h;
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
paint.setStyle(Paint.Style.STROKE);
paint.setARGB(255,0,255,0);
canvas.drawRect(1,1,width -1 ,height -1 ,paint);
}
public void setWidth(){
paint.setStrokeWidth(10);
}
}
活动主文件.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<com.bandiapps.graphicfuture.CustomView
android:id="@+id/cus_1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentEnd="true"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true"
android:layout_alignParentBottom="true"
android:layout_margin="100dp"
/>
</RelativeLayout>
当我要在我设备中运行代码时,它一直关闭。日志猫显示这样的错误。
E FATAL EXCEPTION: main
Process: com.bandiapps.graphicfuture, PID: 25635
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bandiapps.graphicfuture/com.bandiapps.graphicfuture.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.bandiapps.graphicfuture.CustomView.setMessage()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3846)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4022)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2336)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:246)
at android.app.ActivityThread.main(ActivityThread.java:8653)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:602)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1130)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.bandiapps.graphicfuture.CustomView.setMessage()' on a null object reference
at com.bandiapps.graphicfuture.MainActivity.onCreate(MainActivity.java:19)
at android.app.Activity.performCreate(Activity.java:8207)
at android.app.Activity.performCreate(Activity.java:8191)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3819)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4022)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2336)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:246)
at android.app.ActivityThread.main(ActivityThread.java:8653)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:602)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1130)
我使用物理设备来实现此代码。我也是初学者android开发人员。我遵循不同类型的教程,但我不能解决它。我想使用此自定义组件一样,如按钮,编辑文本正常的小部件。我也想把此代码也使用xml。我不能改变它。因为我的目标项目已经开发使用xml布局。我该如何解决它?
1条答案
按热度按时间w6mmgewl1#
问题是您没有将
attrs
传递给super
。将构造函数更改为