大家好，请为我推荐一个解决方案。在准备警报对话框时，看到我得到的错误E / AndroidRuntime：致命异常：main流程：com.techlinemobile.foodbasket，PID：22724java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void android.widget.Button.setOnClickListener（android.view.View $ OnClickListener）'在com.techlinemobile.foodbasket.ItemDetails.showAddedToCartDialogue（ItemDetails.java:162）在com.techlinemobile.foodbasket.ItemDetails.access $ 300（ItemDetails.java:25）在com.techlinemobile.foodbasket.ItemDetails $ 1.onClick（ItemDetails.java:131）在android.view.View.performClick（View.java:6291）在android.view.View $ PerformClick.run（View.java:24931）在android.os.Handler.handleCallback（Handler.java:808）在android.os.Handler.dispatchMessage（Handler.java:101）在android.os.Looper.loop（Looper.java:166）在android.app.ActivityThread.main（ActivityThread.java:7529）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.Zygote $ MethodAndArgsCaller.run（Zygote.java:245）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:921）
查看方法
private void showAddedToCartDialogue（）{
//before inflating the custom alert dialog layout, we will get the current activity viewgroup
ViewGroup viewGroup = findViewById(android.R.id.content);
//then we will inflate the custom alert dialog xml that we created
View dialogView = LayoutInflater.from(this).inflate(R.layout.added_to_cart_dialog, viewGroup, false);
//Now we need an AlertDialog.Builder object
AlertDialog.Builder builder = new AlertDialog.Builder(this);
//setting the view of the builder to our custom view that we already inflated
builder.setView(dialogView);
//finally creating the alert dialog and displaying it
AlertDialog alertDialog = builder.create();
final Button buttonContinue = (Button)alertDialog.getWindow().findViewById(R.id.buttonContinue);
final Button buttonViewCart = (Button)alertDialog.getWindow().findViewById(R.id.buttonViewCart);
buttonContinue.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.d(TAG, "before adding card");
//--------------------------------
//load data to cart
Intent it = new Intent(ItemDetails.this, MainActivity.class);
startActivity(it);
}
});
buttonViewCart.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.d(TAG, "before adding card");
//--------------------------------
//load data to cart
Intent it = new Intent(ItemDetails.this, ShoppingCartActivity.class);
startActivity(it);
}
});
alertDialog.show();
}
查看布局
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="80dp"
android:background="@color/colorPrimary">
<ImageView
android:layout_width="50dp"
android:layout_height="50dp"
android:layout_centerInParent="true"
android:background="@drawable/ic_success" />
</RelativeLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
android:padding="16dp">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/added_to_cart"
android:textAlignment="center"
android:textAppearance="@style/TextAppearance.AppCompat.Headline" />
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dp"
android:text="@string/successfully_added_long"
android:textAlignment="center"
android:textAppearance="@style/TextAppearance.AppCompat.Medium" />
<Button
android:id="@+id/buttonContinue"
android:layout_width="200dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginTop="15dp"
android:background="@drawable/button_background"
android:text="@string/continue_shopping"
android:textColor="@color/colorPrimary" />
<Button
android:id="@+id/buttonViewCart"
android:layout_width="200dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginTop="15dp"
android:background="@drawable/button_background"
android:text="@string/view_cart"
android:textColor="@color/colorPrimary" />
</LinearLayout>
</LinearLayout>
将alertDialog.show()行移到builder.create()下方。或者，您可以使用builder.show()方法立即创建并显示对话框。
错误报告您在空对象上设置了侦听器。您的对话框不可见，因此findViewById返回null。变量buttonContinue和buttonViewCart指向空值。
//before inflating the custom alert dialog layout, we will get the current activity viewgroup
ViewGroup viewGroup = findViewById(android.R.id.content);
//then we will inflate the custom alert dialog xml that we created
View dialogView = LayoutInflater.from(this).inflate(R.layout.added_to_cart_dialog, viewGroup, false);
//Now we need an AlertDialog.Builder object
AlertDialog.Builder builder = new AlertDialog.Builder(this);
//setting the view of the builder to our custom view that we already inflated
builder.setView(dialogView);
//finally creating the alert dialog and displaying it
AlertDialog alertDialog = builder.create();
alertDialog.show(); <---------- show dialog here
final Button buttonContinue = (Button)alertDialog.getWindow().findViewById(R.id.buttonContinue);
final Button buttonViewCart = (Button)alertDialog.getWindow().findViewById(R.id.buttonViewCart);
buttonContinue.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.d(TAG, "before adding card");
//--------------------------------
//load data to cart
Intent it = new Intent(ItemDetails.this, MainActivity.class);
startActivity(it);
}
});
buttonViewCart.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.d(TAG, "before adding card");
//--------------------------------
//load data to cart
Intent it = new Intent(ItemDetails.this, ShoppingCartActivity.class);
startActivity(it);
}
});
使用
Button buttonContinue = dialogView.findViewById(R.id.buttonContinue);
Button buttonViewCart = dialogView.findViewById(R.id.buttonViewCart);
代替
Button buttonContinue = (Button)alertDialog.getWindow().findViewById(R.id.buttonContinue);
并像这样最后创建dailoge。
alertDialog= alertDialogBuilder.create();
alertDialog.show();
alertDialog.getWindow().setLayout(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);