java - 尝试在空对象引用上调用虚拟方法 'void android.view.View.measure(int, int)'

Question

我正在尝试使用

https://github.com/nisrulz/screenshott

用于截图的库。

但它给出了错误。

Attempt to invoke virtual method 'void android.view.View.measure(int,int)' on a null object reference

相对布局:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:ads="http://schemas.android.com/apk/res-auto"
    tools:context="x.y.z"
    android:orientation="vertical"
    android:id="@+id/layoutview">

    <!--
    <com.google.android.gms.ads.AdView
        android:id="@+id/adViewChat2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_alignParentTop="true"
        ads:adSize="SMART_BANNER"
        ads:adUnitId="x">
    </com.google.android.gms.ads.AdView>


-->

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="English"
        android:background="@drawable/shape"
        android:textAppearance="?android:attr/textAppearanceMedium"

        android:layout_marginLeft="@dimen/_15sdp"
        android:layout_marginRight="@dimen/_15sdp"
        android:textAlignment="center"

        android:id="@+id/textviewtop"
        android:layout_marginTop="@dimen/_5sdp"
        android:textColor="#ffffff"
        android:textStyle="bold"


        />




    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/scrollView"
        android:orientation="vertical"
        android:layout_above="@+id/linear"
        android:layout_marginBottom="@dimen/_5sdp"
        android:layout_below="@+id/textviewtop"
        android:layout_marginTop="@dimen/_5sdp"
        >
        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:paddingLeft="@dimen/_15sdp"
            android:background="@drawable/shape"

            android:layout_marginLeft="@dimen/_15sdp"
            android:layout_marginRight="@dimen/_15sdp"
            >

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textAppearance="?android:attr/textAppearanceMedium"
                android:text="@string/welcome"
                android:id="@+id/textView"
                android:textColor="#ffffff"/>

        </RelativeLayout>

    </ScrollView>


    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:layout_alignParentBottom="true"
        android:layout_marginLeft="@dimen/_15sdp"
        android:layout_marginRight="@dimen/_15sdp"
        android:background="@drawable/shape"
        android:id="@+id/linear">



        <EditText
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/editText2"
            android:textColor="#ffffff"
            android:layout_weight="0.9"
            android:hint="Write a message"
            android:textColorHint="#A4A4A4"/>

        <Button
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:text="send"
            android:id="@+id/btn_send"
            android:layout_weight="0.1"
            android:textColor="#ffffff"

            />

    </LinearLayout>



</RelativeLayout>

在OnCreate方法中:

setContentView(R.layout.activity_main);
View myView =(RelativeLayout) findViewById(R.id.layoutview);
Bitmap bitmap_view = 
    ScreenShott.getInstance().takeScreenShotOfView(myView); // problematic line, this line gives the error.

我该如何解决我的问题？如何获得相对布局 View ？

Answer 1

你不能在 onCreate 中这样做。在此 onCreate 方法中，您的布局已被测量和膨胀，但您的 UI 尚未创建。

您必须在 onCreate 之后调用您的代码。例如在按钮事件中:

Button capture_screenshot = findViewById(R.id.button_takeshoot);
        capture_screenshot.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                View myView =(RelativeLayout) findViewById(R.id.layoutview);
                Bitmap bitmap_view = ScreenShott.getInstance().takeScreenShotOfView(myView);
            }
        });

check Activity Lifecycle