[英]Android Java - Receiving null reference error on RecyclerView.setAdapter()
[英]Encountered the error Attempt to invoke virtual method 'RecyclerView.setAdapter(RecyclerView$Adapter)' on a null object reference in Android Studio
当我运行我的代码时,我遇到了问题“Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setAdapter(androidx.recyclerview.widget.RecyclerView$Adapter)' on a null object reference”。 我已经搜索过类似的解决方案,但似乎并没有解决我的错误。
我应该如何修改我的代码?
这是我的 MainActivity.java 代码:
package endlesstaste;
import android.os.Bundle;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.android.material.snackbar.Snackbar;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import java.util.LinkedList;
public class MainActivity extends AppCompatActivity {
private final LinkedList<String> mImagePathList = new LinkedList<>();
private String mDrawableFilePath =
"android.resource://endlesstaste/drawable/";
private RecyclerView mRecyclerView;
ImageListAdapter mAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
for (int i = 1; i <= 5; i++) {
mImagePathList.addLast(mDrawableFilePath + "image" + i);
}
// Get a handle to the RecyclerView.
mRecyclerView = findViewById(R.id.recyclerview);
// Create an adapter and supply the data to be displayed.
mAdapter = new ImageListAdapter(this, mImagePathList);
// Connect the adapter with the RecyclerView.
mRecyclerView.setAdapter(mAdapter);
// Give the RecyclerView a default layout manager.
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
这是我的 ImageListAdapter.java 代码:
package endlesstaste;
import android.os.Bundle;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.android.material.snackbar.Snackbar;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import java.util.LinkedList;
public class MainActivity extends AppCompatActivity {
private final LinkedList<String> mImagePathList = new LinkedList<>();
private String mDrawableFilePath =
"android.resource://endlesstaste/drawable/";
private RecyclerView mRecyclerView;
ImageListAdapter mAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
for (int i = 1; i <= 5; i++) {
mImagePathList.addLast(mDrawableFilePath + "image" + i);
}
// Get a handle to the RecyclerView.
mRecyclerView = findViewById(R.id.recyclerview);
// Create an adapter and supply the data to be displayed.
mAdapter = new ImageListAdapter(this, mImagePathList);
// Connect the adapter with the RecyclerView.
mRecyclerView.setAdapter(mAdapter);
// Give the RecyclerView a default layout manager.
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
你不能打电话
mRecyclerView = findViewById(R.id.recyclerview);
打电话之前
setContentView(R.layout.activity_main);
当您这样做时,对findViewById
的调用将返回 null。 在开始获取视图之前,将setContentView
(以及您使用的super.onCreate
)移动到onCreate
开头。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.