[英]How do I update TextView of CustomListEntry from MainActivity?
我有一個帶有listView(id:listView1)的MainActivity,該適配器具有一個針對listView1行的custom_list_entry.xml(TextView)的適配器。 當行少於填充視圖時(在我的情況下為5個條目),我想填充listView1。 試圖制作另一個類CustomListEntry,以便我可以獲取TextView參考TextView tV = findViewbyId(R.id.customListTV),因為我無法從MainActivity(將setContentView設置為R.layout.activity_main)獲得此內容。 然后在MainActivity類中,獲取CustomListEntry customListEntry = new CustomListEntry()並調用customListEntry.tV.setMinHeight到先前計算的屏幕尺寸高度/ listItemCount,這將希望將屏幕高度除以有多少個條目,並將其分配給每個條目。 問題是運行MainActivity時出現Null指針異常。 請幫忙!
表現:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.sjdav.text_game">
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity"
android:label="@string/app_name"
android:screenOrientation="landscape">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".CustomListEntry"></activity>
</application>
</manifest>
activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.sjdav.text_game.MainActivity"
android:id="@+id/background"
android:weightSum="100"
android:baselineAligned="false">
<RelativeLayout
android:id="@+id/pane_1"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="25">
<ListView
android:id="@+id/listView1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_centerInParent="true"
android:background="#3F45FA">
</ListView>
</RelativeLayout>
<RelativeLayout
android:id="@+id/pane_2"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="25">
<ImageView
android:id="@+id/iV1"
android:layout_width="match_parent"
android:layout_height="100dp"
android:contentDescription="@string/cont_Desc"
android:src="@drawable/pokemon_1"/>
<ListView
android:id="@+id/listView2"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_centerHorizontal="true"
android:background="#FFFFFF"
android:layout_below="@id/iV1">
</ListView>
</RelativeLayout>
<RelativeLayout
android:id="@+id/pane_3"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="25">
<ImageView
android:id="@+id/iV2"
android:layout_width="match_parent"
android:layout_height="100dp"
android:contentDescription="@string/cont_Desc"
android:src="@drawable/pokemon_3"/>
<ListView
android:id="@+id/listView3"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_centerHorizontal="true"
android:background="#FFFFFF"
android:layout_below="@id/iV2">
</ListView>
</RelativeLayout>
<RelativeLayout
android:id="@+id/pane_4"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="25">
</RelativeLayout>
</LinearLayout>
custom_list_entry.xml:
<?xml version="1.0" encoding="utf-8"?>
<TextView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
tools:context="com.example.sjdav.text_game.CustomListEntry"
android:id="@+id/customListTV"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:textSize="20sp"
android:textColor="@color/colorAccent"
android:gravity="center_vertical"
android:textAlignment="center"
android:padding="8dp">
</TextView>
MainActivity.java:
package com.example.sjdav.text_game;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
public CustomListEntry customListEntry = new CustomListEntry();
public float listItemHeight;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getSupportActionBar() != null) {
getSupportActionBar().hide();
}
setContentView(R.layout.activity_main);
Log.i(TAG, "onCreate: MA >> Started..");
DisplayMetrics metrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(metrics);
float density = metrics.density;
float width = metrics.widthPixels / density;
float height = metrics.heightPixels / density;
Log.i(TAG, "onCreate: MA >> width: " + width);
Log.i(TAG, "onCreate: MA >> hehight: " + height);
ListView listView1 = findViewById(R.id.listView1);
final ArrayList<String> menu = new ArrayList<>();
menu.add(getString(R.string.start));
menu.add(getString(R.string.settings));
menu.add(getString(R.string.about));
menu.add(getString(R.string.images));
menu.add(getString(R.string.credits));
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.custom_list_entry, menu);
listView1.setAdapter(adapter);
int listItemsCount = listView1.getAdapter().getCount();
Log.i(TAG, "onCreate: MA >> listVew1 item count: " + listItemsCount);
float custom_dimen = getResources().getDimension(R.dimen.custom_list_entry_height) / density;
Log.i(TAG, "onCreate: MA >> list dimen: " + custom_dimen);
listItemHeight = height / listItemsCount;
Log.i(TAG, "onCreate: MA >> listView1 listItemHeight: " + listItemHeight);
customListEntry.tV.setMinHeight((int)listItemHeight);
listView1.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Log.i(TAG, "onItemClick: MA >> menu: " + menu.get(position));
// When click on menu item, show/hide other views by setting visibility and focusable and clickable
}
});
}
}
CustomListEntry.java:
package com.example.sjdav.text_game;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.TextView;
public class CustomListEntry extends AppCompatActivity {
public TextView tV;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getSupportActionBar() != null) {
getSupportActionBar().hide();
}
setContentView(R.layout.custom_list_entry);
tV = findViewById(R.id.customListTV);
}
}
你做錯了 創建一個自定義適配器,並在自定義適配器上擴展視圖。
這對你有幫助
public class ListCustomAdapter extends ArrayAdapter<String> {
private TextView customListTV;
public ListCustomAdapter(Context context, int resource, ArrayList<String> objects) {
super(context, resource, objects);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
try{
LayoutInflater inflater = (LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.custom_list_entry,null,false);
customListTV = (TextView) convertView.findViewById(R.id.customListTV);
String data = getItem(position);
customListTV.setText(data);
}catch (Exception e){
e.printStackTrace();
}
return convertView;
}
}
在您的主要活動中,創建適配器類的對象
ListCustomAdapter adapter = new ListCustomAdapter(this,R.layout.activity_main,menu);
setListAdapter(adapter);
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