我正在尝试在listView为空时显示图像，但是不幸的是，每当列表为空时，它都不会显示该图像。
我试图将setEmptyView移入oncreate，然后再尝试检查游标是否为空，然后调用setemptyview方法
围栏活动 在此活动中，我尝试使用setEmptyView方法。
public class FenceActivity extends AppCompatActivity {
List<Fence> fenceList;
SQLiteDatabase sqLiteDatabase;
ListView listViewFences;
FenceAdapter fenceAdapter;
DataBaseHelper dataBaseHelper;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.savedfences);
listViewFences = findViewById(R.id.fencesListView);
fenceList = new ArrayList<>();
showFencesFromDatabase();
}
public void showFencesFromDatabase() {
dataBaseHelper = new DataBaseHelper(this);
Cursor cursor = dataBaseHelper.getAllData();
if (cursor.moveToFirst()) {
do {
fenceList.add(new Fence(cursor.getInt(0), cursor.getDouble(1), cursor.getDouble(2), cursor.getInt(3)));
} while (cursor.moveToNext());
}
cursor.close();
fenceAdapter = new FenceAdapter(FenceActivity.this, R.layout.list_layout_fences, fenceList);
listViewFences.setAdapter(fenceAdapter);
listViewFences.setEmptyView(findViewById(R.id.emptyElement));
}
public void reloadFencesFromDatabase() {
dataBaseHelper = new DataBaseHelper(this);
Cursor cursor = dataBaseHelper.getAllData();
fenceList.clear();
if (cursor.moveToFirst()) {
do {
fenceList.add(new Fence(cursor.getInt(0), cursor.getDouble(1), cursor.getDouble(2), cursor.getInt(3)));
} while (cursor.moveToNext());
}
cursor.close();
fenceAdapter = new FenceAdapter(FenceActivity.this, R.layout.list_layout_fences, fenceList);
listViewFences.setAdapter(fenceAdapter);
listViewFences.setEmptyView(findViewById(R.id.emptyElement));
}
}
Savedfences.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent" android:layout_height="match_parent">
<ListView
android:id="@+id/fencesListView"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<ImageView
android:id="@+id/emptyElement"
android:layout_width="200dp"
android:layout_height="200dp"
android:dividerHeight="1dp"
android:visibility="gone"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true"/>
</RelativeLayout>
适配器类
public class FenceAdapter extends ArrayAdapter<Fence> {
Context context;
int listLayoutRes;
List<Fence> fenceList;
DataBaseHelper dataBaseHelper;
FenceActivity fenceActivity;
public FenceAdapter(Context context, int listLayoutRes, List<Fence> fenceList) {
super(context, listLayoutRes, fenceList);
this.context = context;
this.listLayoutRes = listLayoutRes;
this.fenceList = fenceList;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
LayoutInflater mInflater = (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
convertView = mInflater.inflate(R.layout.list_layout_fences, null);
}
final Fence fence = fenceList.get(position);
TextView textViewSno = convertView.findViewById(R.id.textViewSnoLabel);
TextView textViewLat = convertView.findViewById(R.id.textViewLatitudeValue);
TextView textViewLon = convertView.findViewById(R.id.textViewLongitudeValue);
TextView textViewRadi = convertView.findViewById(R.id.textViewRadiusValue);
textViewSno.setText(Integer.toString(fence.getSno()));
textViewLat.setText(String.valueOf(fence.getLat()));
textViewLon.setText(String.valueOf(fence.getLon()));
textViewRadi.setText(Integer.toString(fence.getRadius()));
Button buttonDel = convertView.findViewById(R.id.buttonDeleteFence);
buttonDel.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
AlertDialog.Builder builder = new AlertDialog.Builder(context);
builder.setTitle("Are you sure");
builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
dataBaseHelper = new DataBaseHelper(context);
fenceActivity = (FenceActivity)context;
dataBaseHelper.deleteDataById(fence);
fenceActivity.reloadFencesFromDatabase();
}
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
}
});
AlertDialog dialog = builder.create();
dialog.show();
}
});
return convertView;
}
}
当列表为空时，我可以进行哪些更改以显示该图像。
答案 0 :(得分：1)
public class FenceActivity extends AppCompatActivity {
List<Fence> fenceList;
SQLiteDatabase sqLiteDatabase;
ListView listViewFences;
FenceAdapter fenceAdapter;
DataBaseHelper dataBaseHelper;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.savedfences);
listViewFences = findViewById(R.id.fencesListView);
fenceList = new ArrayList<>();
showFencesFromDatabase();
}
public void showFencesFromDatabase() {
dataBaseHelper = new DataBaseHelper(this);
Cursor cursor = dataBaseHelper.getAllData();
if (cursor.moveToFirst()) {
do {
fenceList.add(new Fence(cursor.getInt(0), cursor.getDouble(1), cursor.getDouble(2), cursor.getInt(3)));
} while (cursor.moveToNext());
}
cursor.close();
fenceAdapter = new FenceAdapter(FenceActivity.this, R.layout.list_layout_fences, fenceList);
listViewFences.setAdapter(fenceAdapter);
listViewFences.setEmptyView(findViewById(R.id.emptyElement));
}
public void reloadFencesFromDatabase() {
dataBaseHelper = new DataBaseHelper(this);
Cursor cursor = dataBaseHelper.getAllData();
fenceList.clear();
if (cursor.moveToFirst()) {
do {
fenceList.add(new Fence(cursor.getInt(0), cursor.getDouble(1), cursor.getDouble(2), cursor.getInt(3)));
} while (cursor.moveToNext());
}
cursor.close();
fenceAdapter = new FenceAdapter(FenceActivity.this, R.layout.list_layout_fences, fenceList);
listViewFences.setAdapter(fenceAdapter);
listViewFences.setEmptyView(findViewById(R.id.emptyElement));
}
}
添加而不是listViewFences.setEmptyView(findViewById(R.id.emptyElement));
listViewFences.setVisibility(fenceList.size>0?View.VISIBLE:View.GONE);
emptyElement.setVisibility(fenceList.size>0?View.GONE:View.VISIBLE);
还要在活动中定义emptyElement view。
答案 1 :(得分：0)
尝试在设置适配器之前先设置空视图
fenceAdapter = new FenceAdapter(FenceActivity.this, R.layout.list_layout_fences, fenceList);
listViewFences.setEmptyView(findViewById(R.id.emptyElement));
listViewFences.setAdapter(fenceAdapter);
答案 2 :(得分：0)
在您的代码中进行此更改-
typedef struct
{
packed_float3 position;
packed_float3 normal;
packed_float2 texCoord1;
packed_float3 tangent;
packed_float3 bitagent;
packed_float4 vertColor;
} vertex_t;
typedef struct
{
float4 position [[position]] , vertexPosition_ws;
float2 uv,texture2UV;
float hasLighting;
float pointSize [[point_size]];
float vertexDepth, reflection;
float hasMeshColor;
float shadowDarkness, transparency;
float2 pointCoord [[ point_coord ]];
float4 eyeVec, lightDir, lightColor;
float3 meshColor;
float3 T;
float3 B;
float3 N;
} ColorInOut;
vertex ColorInOut Mesh_Vertex(device vertex_t* vertex_array [[ buffer(0) ]],
constant float4x4& vp [[ buffer(SHADER_MESH_mvp) ]],
constant MatArray* model [[ buffer(SHADER_MESH_model) ]],
constant float4x4& lvp [[ buffer(SHADER_MESH_lightViewProjMatrix) ]],
constant packed_float3& eyePos [[ buffer(SHADER_MESH_eyePos) ]],
constant float& shadowDarkness [[ buffer(SHADER_MESH_shadowDarkness) ]],
constant float *hasMeshColor [[ buffer(SHADER_MESH_hasMeshColor) ]],
constant float *reflectionValue [[ buffer(SHADER_MESH_reflectionValue) ]],
constant float *transparency [[ buffer(SHADER_MESH_transparency) ]],
constant float *hasLighting [[ buffer(SHADER_MESH_hasLighting) ]],
constant float *uvScaleValue [[ buffer(SHADER_MESH_uvScale) ]],
constant float3Struct *meshColor [[buffer(SHADER_MESH_meshColor)]],
unsigned int vid [[ vertex_id ]],
unsigned int iId [[ instance_id ]]
)
{
float4 vertexPosition_ws = model[iId].data * float4(float3(vertex_array[vid].position), 1.0);
float4 vertColor = float4(vertex_array[vid].vertColor);
float3 tangent = float3(vertex_array[vid].tangent);
float3 bitangent = float3(vertex_array[vid].bitagent);
float3 normal = float3(vertex_array[vid].normal);
ColorInOut out;
out.hasMeshColor = hasMeshColor[iId];
out.meshColor = (meshColor[iId].data[0] == -1.0) ? vertColor.xyz : float3(meshColor[iId].data);
out.reflection = reflectionValue[iId];
out.T = normalize(float3(model[iId].data * float4(tangent, 0.0)));
out.B = normalize(float3(model[iId].data * float4(bitangent, 0.0)));
out.N = normalize(float3(model[iId].data * float4(normal, 0.0)));
out.vertexPosition_ws = vertexPosition_ws;
out.transparency = transparency[iId];
out.hasLighting = hasLighting[iId];
out.position = vp * vertexPosition_ws;
out.uv = vertex_array[vid].texCoord1 * uvScaleValue[iId];
out.shadowDarkness = 0.0;
if(bool(hasLighting[iId])) {
float4 vertexLightCoord = lvp * vertexPosition_ws;
float4 texCoords = vertexLightCoord/vertexLightCoord.w;
out.texture2UV = float4((texCoords / 2.0) + 0.5).xy;
out.texture2UV.y = (1.0 - out.texture2UV.y); // need to flip metal texture vertically
out.vertexDepth = texCoords.z;
out.shadowDarkness = shadowDarkness;
}
float4 eye_position_ws = vertexPosition_ws - float4(float3(eyePos), 1.0);
out.eyeVec = normalize(eye_position_ws);
return out;
}