Question

在为我的CardView设置onclick列表器时获得Nullpointer异常。

错误是：

原因：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“ void android.support.v7.widget.CardView.setOnClickListener（android.view.View $ OnClickListener）” 在com.jaysurya.project_scrollwithtap.MainActivity.onCreate（MainActivity.java:27）

这是我的 mainactivity.java

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.CardView;
import android.view.View;


public class MainActivity extends AppCompatActivity {

CardView chap1,chap2,chap3,chap4,chap5;
int chapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    chap1 = findViewById(R.id.chap1);
    chap2 = findViewById(R.id.chap2);
    chap3 = findViewById(R.id.chap3);
    chap4 = findViewById(R.id.chap4);
    chap5 = findViewById(R.id.chap5);


    chap1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            chapter = 1;
            openchapters(chapter);
        }
    });
    chap2.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            chapter = 2;
            openchapters(chapter);
        }
    });
    chap3.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            chapter = 3;
            openchapters(chapter);
        }
    });
    chap4.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            chapter = 4;
            openchapters(chapter);
        }
    });
    chap5.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            chapter = 5;
            openchapters(chapter);
        }
    });

}
private void openchapters(int chapter){
    Intent intent = new Intent(this, Main1Activity.class);
    intent.putExtra("chapter_no",chapter);
    startActivity(intent);
}
}

这是我的 activity_main.xml

ScrollView 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="wrap_content"
tools:context=".MainActivity">

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:scaleType="fitXY"
    android:background="@drawable/jhyti"
    android:orientation="vertical">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <ImageView
            android:id="@+id/imageView1"
            android:layout_width="match_parent"
            android:layout_height="185dp"
            android:layout_alignParentStart="true"
            android:layout_alignParentTop="true"
            android:layout_marginStart="0dp"
            android:layout_marginTop="0dp"
            android:gravity="center_vertical"
            android:src="@drawable/logo" />

    </RelativeLayout>

    <GridLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:alignmentMode="alignMargins"
        android:columnCount="1"
        android:columnOrderPreserved="false"
        android:padding="14dp">

        <!--ROW 1 - -!>

        <!- -CARD 1-->
        <android.support.v7.widget.CardView
            android:id="@+id/chap1"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_columnWeight="1"
            android:layout_marginBottom="16dp"
            android:layout_marginLeft="16dp"
            android:layout_marginRight="16dp"
            android:layout_marginTop="20dp"
            android:layout_rowWeight="1"
            android:clickable="true"
            android:focusable="true"
            android:foreground="?attr/selectableItemBackground"
            android:stateListAnimator="@animator/lift_on_touch"
            app:cardCornerRadius="8dp"
            app:cardElevation="8dp"
            app:cardPreventCornerOverlap="false"
            app:cardUseCompatPadding="true"
            app:contentPadding="1dp">

            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center_horizontal|center_vertical"
                android:layout_margin="16dp"
                android:orientation="vertical">

                <ImageView
                    android:layout_width="150dp"
                    android:layout_height="74dp"
                    android:layout_gravity="center_horizontal"
                    android:src="@drawable/p2" />

                <TextView
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:gravity="center"
                    android:text="CHAPTER 1"
                    android:textColor="@color/black"
                    android:textSize="18sp"
                    android:textStyle="bold|italic"
                    tools:ignore="HardcodedText" />
            </LinearLayout>

            <TextView
                android:id="@+id/textView2"
                android:layout_width="163dp"
                android:layout_height="wrap_content"
                android:text="CHAPTER 1"
                android:textSize="18sp"
                android:textColor="@color/black"
                android:textStyle="bold|italic"
                tools:ignore="HardcodedText" />


        </android.support.v7.widget.CardView>

        <!--CARD 2-->
        <android.support.v7.widget.CardView
            android:id="@+id/chap2"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_columnWeight="1"
            android:layout_marginBottom="16dp"
            android:layout_marginLeft="16dp"
            android:layout_marginRight="16dp"
            android:layout_rowWeight="1"
            android:clickable="true"
            android:focusable="true"
            android:foreground="?attr/selectableItemBackground"
            android:stateListAnimator="@animator/lift_on_touch"
            app:cardCornerRadius="8dp"
            app:cardElevation="8dp"
            app:cardPreventCornerOverlap="false"
            app:cardUseCompatPadding="true"

            app:contentPadding="1dp">

            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center_horizontal|center_vertical"
                android:layout_margin="16dp"
                android:orientation="vertical">

                <ImageView
                    android:layout_width="150dp"
                    android:layout_height="74dp"
                    android:layout_gravity="center_horizontal"
                    android:src="@drawable/p4" />

                <TextView
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:gravity="center"
                    android:text="CHAPTER 2"
                    android:textColor="@color/black"
                    android:textSize="18sp"
                    android:textStyle="bold|italic"
                    tools:ignore="HardcodedText" />
            </LinearLayout>

            <TextView
                android:id="@+id/textView3"
                android:layout_width="172dp"
                android:layout_height="wrap_content"
                android:text="CHAPTER 2"
                android:textSize="18sp"
                android:textColor="@color/black"
                android:textStyle="bold|italic"
                tools:ignore="HardcodedText"/>


        </android.support.v7.widget.CardView>


        <!--CARD 3-->


        <android.support.v7.widget.CardView
            android:id="@+id/chap3"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_columnWeight="1"
            android:layout_marginBottom="16dp"
            android:layout_marginLeft="16dp"
            android:layout_marginRight="16dp"
            android:layout_rowWeight="1"
            android:clickable="true"
            android:focusable="true"
            android:foreground="?attr/selectableItemBackground"
            android:stateListAnimator="@animator/lift_on_touch"
            app:cardCornerRadius="8dp"
            app:cardElevation="8dp"
            app:cardPreventCornerOverlap="false"
            app:cardUseCompatPadding="true"

            app:contentPadding="1dp">

            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center_horizontal|center_vertical"
                android:layout_margin="16dp"
                android:orientation="vertical">

                <ImageView
                    android:layout_width="150dp"
                    android:layout_height="74dp"
                    android:layout_gravity="center_horizontal"
                    android:src="@drawable/p5" />

                <TextView
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:text="CHAPTER 3"
                    android:textAlignment="center"
                    android:textColor="@color/black"
                    android:textSize="18sp"
                    android:textStyle="bold|italic" />
            </LinearLayout>

            <TextView
                android:id="@+id/textView4"
                android:layout_width="155dp"
                android:layout_height="33dp"
                android:text="CHAPTER 3"
                android:textSize="18sp"
                android:textColor="@color/black"
                android:textStyle="bold|italic"
                tools:ignore="HardcodedText"/>


        </android.support.v7.widget.CardView>

        <!--CARD 4-->
        <android.support.v7.widget.CardView
            android:id="@+id/chap4"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_columnWeight="1"
            android:layout_marginBottom="16dp"
            android:layout_marginLeft="16dp"
            android:layout_marginRight="16dp"
            android:layout_rowWeight="1"
            android:clickable="true"
            android:focusable="true"
            android:foreground="?attr/selectableItemBackground"
            android:stateListAnimator="@animator/lift_on_touch"
            app:cardCornerRadius="8dp"
            app:cardElevation="8dp"
            app:cardPreventCornerOverlap="false"
            app:cardUseCompatPadding="true"

            app:contentPadding="1dp">

            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center_horizontal|center_vertical"
                android:layout_margin="16dp"
                android:orientation="vertical">

                <ImageView
                    android:layout_width="150dp"
                    android:layout_height="74dp"
                    android:layout_gravity="center_horizontal"
                    android:src="@drawable/p3" />

                <TextView
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:text="CHAPTER 4"
                    android:textAlignment="center"
                    android:textColor="@color/black"
                    android:textSize="18sp"
                    android:textStyle="bold|italic" />
            </LinearLayout>

            <TextView
                android:id="@+id/textView5"
                android:layout_width="155dp"
                android:layout_height="wrap_content"
                android:text="CHAPTER 4"
                android:textSize="18sp"
                android:textColor="@color/black"
                android:textStyle="bold|italic"
                tools:ignore="HardcodedText" />


        </android.support.v7.widget.CardView>

        <!--CARD 5-->
        <android.support.v7.widget.CardView
            android:id="@+id/chap5"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_columnWeight="1"
            android:layout_marginBottom="16dp"
            android:layout_marginLeft="16dp"
            android:layout_marginRight="16dp"
            android:layout_rowWeight="1"
            android:clickable="true"
            android:focusable="true"
            android:foreground="?attr/selectableItemBackground"
            android:stateListAnimator="@animator/lift_on_touch"
            app:cardCornerRadius="8dp"
            app:cardElevation="8dp"
            app:cardPreventCornerOverlap="false"
            app:cardUseCompatPadding="true"

            app:contentPadding="1dp">

            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center_horizontal|center_vertical"
                android:layout_margin="16dp"
                android:orientation="vertical">

                <ImageView
                    android:layout_width="191dp"
                    android:layout_height="74dp"
                    android:layout_gravity="center_horizontal"
                    android:src="@drawable/p1" />

                <TextView
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:text="CHAPTER 5"
                    android:textAlignment="center"
                    android:textColor="@color/black"
                    android:textSize="18sp"
                    android:textStyle="bold|italic"
                    tools:ignore="HardcodedText" />
            </LinearLayout>

            <TextView
                android:id="@+id/textView"
                android:layout_width="188dp"
                android:layout_height="wrap_content"
                android:text="CHAPTER 5"
                android:textSize="18sp"
                android:textColor="@color/black"
                android:textStyle="bold|italic"
                tools:ignore="HardcodedText" />


        </android.support.v7.widget.CardView>


    </GridLayout>

</LinearLayout>
</ScrollView>

Answer 1

对于java.lang.OutOfMemoryError，您可以在清单文件中添加以下行：

android:largeHeap="true"

像这样：

<application
    ......
    android:largeHeap="true"
    ......
</application>

有关大堆以及何时使用它的更多详细信息，请参考this答案。

尝试调用虚拟方法'void android.support.v7.widget.CardView.setOnClickListener

1 个答案: