[英]What's wrong with my implementation of RecyclerView?
我正在關注Android開發人員關於如何設置RecyclerView的說明,但遇到一些錯誤,例如android.widget.LinearLayout cannot be cast to android.widget.TextView
。
從這里獲取的代碼: RecyclerView
這是我的代碼,包括所有必需的文件:
MainActivity.java:
package com.example.lastlocation.recyclerviewer;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
public class MainActivity extends AppCompatActivity {
private RecyclerView mRecyclerView;
private RecyclerView.Adapter mAdapter;
private RecyclerView.LayoutManager mLayoutManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
// use this setting to improve performance if you know that changes
// in content do not change the layout size of the RecyclerView
mRecyclerView.setHasFixedSize(true);
// use a linear layout manager
mLayoutManager = new LinearLayoutManager(this);
mRecyclerView.setLayoutManager(mLayoutManager);
String[] myDataset = new String[5];
myDataset[0] = "Data0";
myDataset[1] = "Data1";
myDataset[2] = "Data2";
myDataset[3] = "Data3";
myDataset[4] = "Data4";
// specify an adapter (see also next example)
mAdapter = new MyAdapter(myDataset);
mRecyclerView.setAdapter(mAdapter);
}
}
這是MyAdapter.java:
package com.example.lastlocation.recyclerviewer;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {
private String[] mDataset;
// Provide a reference to the views for each data item
// Complex data items may need more than one view per item, and
// you provide access to all the views for a data item in a view holder
public static class MyViewHolder extends RecyclerView.ViewHolder {
// each data item is just a string in this case
public TextView mTextView;
public MyViewHolder(TextView v) {
super(v);
mTextView = v;
}
}
// Provide a suitable constructor (depends on the kind of dataset)
public MyAdapter(String[] myDataset) {
mDataset = myDataset;
}
// Create new views (invoked by the layout manager)
@Override
public MyAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent,
int viewType) {
TextView v = (TextView) LayoutInflater.from(parent.getContext())
.inflate(R.layout.my_text_view, parent, false);
MyViewHolder vh = new MyViewHolder(v);
return vh;
}
// Replace the contents of a view (invoked by the layout manager)
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
// - get element from your dataset at this position
// - replace the contents of the view with that element
holder.mTextView.setText(mDataset[position]);
}
// Return the size of your dataset (invoked by the layout manager)
@Override
public int getItemCount() {
return mDataset.length;
}
}
這是activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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">
<View
android:id="@+id/view"
android:layout_width="386dp"
android:layout_height="135dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ImageView
android:id="@+id/imageView"
android:layout_width="66dp"
android:layout_height="64dp"
android:layout_marginTop="24dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="@+id/view"
app:srcCompat="@android:color/holo_orange_dark" />
<TextView
android:id="@+id/textView2"
android:layout_width="68dp"
android:layout_height="30dp"
android:layout_marginTop="8dp"
android:text="John Doe"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/imageView" />
<!-- A RecyclerView with some commonly used attributes -->
<android.support.v7.widget.RecyclerView
android:id="@+id/my_recycler_view"
android:layout_width="375dp"
android:layout_height="367dp"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginLeft="8dp"
android:layout_marginRight="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="4dp"
android:scrollbars="vertical"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.428"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/view"
app:layout_constraintVertical_bias="1.0" />
</android.support.constraint.ConstraintLayout>
這是一個名為my_text_view.xml的單個文本視圖的xml:
<?xml version="1.0" encoding="utf-8"?>
<!-- Layout for a single list item -->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="16dp">
<TextView
android:id="@+id/my_text_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
/>
</LinearLayout>
如您所見,我幾乎從Android Developer的網站復制了代碼,但我仍然不知道問題出在哪里。
public static class MyViewHolder extends RecyclerView.ViewHolder {
// each data item is just a string in this case
public TextView mTextView;
public MyViewHolder(TextView v) {
super(v);
mTextView = v;
}
}
// Provide a suitable constructor (depends on the kind of dataset)
public MyAdapter(String[] myDataset) {
mDataset = myDataset;
}
問題是您的ViewHolder構造函數中應該是這樣的
public static class MyViewHolder extends RecyclerView.ViewHolder {
// each data item is just a string in this case
public TextView mTextView;
public MyViewHolder(View v) {
super(v);
mTextView = v.findViewById(R.id.your_text_view_id);
}
}
@Override
public MyAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent,
int viewType) {
View v = (TextView) LayoutInflater.from(parent.getContext())
.inflate(R.layout.my_text_view, parent, false);
MyViewHolder vh = new MyViewHolder(v);
return vh;
}
您嘗試將LinearLayout(即構造函數中的View)分配給TextView,並且崩潰。 這樣可以解決問題。 在ViewHolder中作為構造函數參數接收的視圖是ViewHolder的根視圖,在本例中為LinearLayout,從該根視圖中可以找到其他視圖。
您錯誤地誇大了行視圖,因此沒有以正確的方式在viewholder中分配視圖,請如下更改代碼
@Override
public UserListAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
LayoutInflater inflater = LayoutInflater.from(parent.getContext());
ViewHolder vh = new ViewHolder((inflater.inflate(R.layout.your_row_layout, parent, false)));
return vh;
}
然后按如下所示更改您的觀看者
public static class MyViewHolder extends RecyclerView.ViewHolder {
// each data item is just a string in this case
public TextView mTextView;
public MyViewHolder(View v) {
super(v);
mTextView = v.findViewById(R.id.my_text_view);
}
}
只是,您需要通過以下方式更改onCreateViewHolder方法:
View view = LayoutInflater.from(parent.getContext())
.inflate(R.layout.my_text_view, parent, false);
return view;
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