错误日志
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.wechat, PID: 3124
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.wechat/com.example.wechat.ListViewActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at com.example.wechat.ListViewActivity.onCreate(ListViewActivity.java:16)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
MyListAdapter.java
package com.example.wechat;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;
import com.bumptech.glide.Glide;
//Adapter 适配器 用来写列表每一行,每一个网格是什么样子的
public class MyListAdapter extends BaseAdapter {
protected Context mContext;
protected LayoutInflater mLayoutInflater;
public MyListAdapter(Context context){
this.mContext = context;
mLayoutInflater = LayoutInflater.from(context);
}
@Override
//列表长度
public int getCount() {
return 10;
}
@Override
public Object getItem(int position) {
return null;
}
@Override
public long getItemId(int position) {
return 0;
}
static class ViewHolder{
public ImageView imageView;
public TextView tv_title,tv_time,tv_content;
}
@Override
//列表每一行是什么样子
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder = null;
if (convertView == null){
convertView =mLayoutInflater.inflate(R.layout.layout_list_item,null);
holder = new ViewHolder();
holder.imageView = convertView.findViewById(R.id.iv_1);
holder.tv_title = convertView.findViewById(R.id.tv_title);
holder.tv_time = convertView.findViewById(R.id.tv_time);
holder.tv_content = convertView.findViewById(R.id.tv_content);
convertView.setTag(holder);
}else {
holder = (ViewHolder) convertView.getTag();
}
//给控件赋值
holder.tv_title.setText("这是标题");
holder.tv_time.setText("2088-08-08");
holder.tv_content.setText("这是内容");
Glide.with(mContext).load("https://blog.hkmovie6.com/wp-content/uploads/2018/12/946848-1024x576.jpg").into(holder.imageView);
return convertView;
}
}
ListViewActivity.java
package com.example.wechat;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ListView;
public class ListViewActivity extends AppCompatActivity {
protected ListView mLv1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list_view);
mLv1 = findViewById(R.id.lv_1);
mLv1.setAdapter(new MyListAdapter(com.example.wechat.ListViewActivity.this));
}
}